author | dl |
Wed, 23 Feb 2011 14:56:44 +0000 | |
changeset 8544 | 225896f7b33c |
parent 7976 | f273c0d04215 |
child 9242 | ef138d47df58 |
permissions | -rw-r--r-- |
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/* |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Oracle designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Oracle in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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*/ |
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/* |
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* This file is available under and governed by the GNU General Public |
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* License version 2 only, as published by the Free Software Foundation. |
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* However, the following notice accompanied the original version of this |
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* file: |
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* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/licenses/publicdomain |
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*/ |
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package java.util.concurrent; |
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import java.util.concurrent.locks.*; |
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import java.util.concurrent.atomic.*; |
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import java.util.*; |
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/** |
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* An {@link ExecutorService} that executes each submitted task using |
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* one of possibly several pooled threads, normally configured |
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* using {@link Executors} factory methods. |
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* |
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* <p>Thread pools address two different problems: they usually |
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* provide improved performance when executing large numbers of |
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* asynchronous tasks, due to reduced per-task invocation overhead, |
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* and they provide a means of bounding and managing the resources, |
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* including threads, consumed when executing a collection of tasks. |
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* Each {@code ThreadPoolExecutor} also maintains some basic |
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* statistics, such as the number of completed tasks. |
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* |
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* <p>To be useful across a wide range of contexts, this class |
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* provides many adjustable parameters and extensibility |
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* hooks. However, programmers are urged to use the more convenient |
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* {@link Executors} factory methods {@link |
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* Executors#newCachedThreadPool} (unbounded thread pool, with |
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* automatic thread reclamation), {@link Executors#newFixedThreadPool} |
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* (fixed size thread pool) and {@link |
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* Executors#newSingleThreadExecutor} (single background thread), that |
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* preconfigure settings for the most common usage |
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* scenarios. Otherwise, use the following guide when manually |
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* configuring and tuning this class: |
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* |
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* <dl> |
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* |
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* <dt>Core and maximum pool sizes</dt> |
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* |
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* <dd>A {@code ThreadPoolExecutor} will automatically adjust the |
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* pool size (see {@link #getPoolSize}) |
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* according to the bounds set by |
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* corePoolSize (see {@link #getCorePoolSize}) and |
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* maximumPoolSize (see {@link #getMaximumPoolSize}). |
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* |
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* When a new task is submitted in method {@link #execute}, and fewer |
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* than corePoolSize threads are running, a new thread is created to |
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* handle the request, even if other worker threads are idle. If |
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* there are more than corePoolSize but less than maximumPoolSize |
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* threads running, a new thread will be created only if the queue is |
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* full. By setting corePoolSize and maximumPoolSize the same, you |
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* create a fixed-size thread pool. By setting maximumPoolSize to an |
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* essentially unbounded value such as {@code Integer.MAX_VALUE}, you |
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* allow the pool to accommodate an arbitrary number of concurrent |
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* tasks. Most typically, core and maximum pool sizes are set only |
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* upon construction, but they may also be changed dynamically using |
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* {@link #setCorePoolSize} and {@link #setMaximumPoolSize}. </dd> |
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* |
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* <dt>On-demand construction</dt> |
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* |
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* <dd> By default, even core threads are initially created and |
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* started only when new tasks arrive, but this can be overridden |
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* dynamically using method {@link #prestartCoreThread} or {@link |
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* #prestartAllCoreThreads}. You probably want to prestart threads if |
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* you construct the pool with a non-empty queue. </dd> |
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* |
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* <dt>Creating new threads</dt> |
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* |
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* <dd>New threads are created using a {@link ThreadFactory}. If not |
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* otherwise specified, a {@link Executors#defaultThreadFactory} is |
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* used, that creates threads to all be in the same {@link |
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* ThreadGroup} and with the same {@code NORM_PRIORITY} priority and |
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* non-daemon status. By supplying a different ThreadFactory, you can |
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* alter the thread's name, thread group, priority, daemon status, |
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* etc. If a {@code ThreadFactory} fails to create a thread when asked |
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* by returning null from {@code newThread}, the executor will |
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* continue, but might not be able to execute any tasks. Threads |
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* should possess the "modifyThread" {@code RuntimePermission}. If |
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* worker threads or other threads using the pool do not possess this |
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* permission, service may be degraded: configuration changes may not |
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* take effect in a timely manner, and a shutdown pool may remain in a |
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* state in which termination is possible but not completed.</dd> |
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* |
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* <dt>Keep-alive times</dt> |
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* |
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* <dd>If the pool currently has more than corePoolSize threads, |
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* excess threads will be terminated if they have been idle for more |
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* than the keepAliveTime (see {@link #getKeepAliveTime}). This |
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* provides a means of reducing resource consumption when the pool is |
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* not being actively used. If the pool becomes more active later, new |
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* threads will be constructed. This parameter can also be changed |
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* dynamically using method {@link #setKeepAliveTime}. Using a value |
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* of {@code Long.MAX_VALUE} {@link TimeUnit#NANOSECONDS} effectively |
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* disables idle threads from ever terminating prior to shut down. By |
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* default, the keep-alive policy applies only when there are more |
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* than corePoolSizeThreads. But method {@link |
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* #allowCoreThreadTimeOut(boolean)} can be used to apply this |
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* time-out policy to core threads as well, so long as the |
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* keepAliveTime value is non-zero. </dd> |
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* |
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* <dt>Queuing</dt> |
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* |
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* <dd>Any {@link BlockingQueue} may be used to transfer and hold |
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* submitted tasks. The use of this queue interacts with pool sizing: |
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* |
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* <ul> |
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* |
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* <li> If fewer than corePoolSize threads are running, the Executor |
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* always prefers adding a new thread |
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* rather than queuing.</li> |
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* |
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* <li> If corePoolSize or more threads are running, the Executor |
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* always prefers queuing a request rather than adding a new |
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* thread.</li> |
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* |
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* <li> If a request cannot be queued, a new thread is created unless |
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* this would exceed maximumPoolSize, in which case, the task will be |
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* rejected.</li> |
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* |
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* </ul> |
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* |
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* There are three general strategies for queuing: |
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* <ol> |
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* |
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* <li> <em> Direct handoffs.</em> A good default choice for a work |
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* queue is a {@link SynchronousQueue} that hands off tasks to threads |
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* without otherwise holding them. Here, an attempt to queue a task |
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* will fail if no threads are immediately available to run it, so a |
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* new thread will be constructed. This policy avoids lockups when |
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* handling sets of requests that might have internal dependencies. |
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* Direct handoffs generally require unbounded maximumPoolSizes to |
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* avoid rejection of new submitted tasks. This in turn admits the |
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* possibility of unbounded thread growth when commands continue to |
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* arrive on average faster than they can be processed. </li> |
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* |
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* <li><em> Unbounded queues.</em> Using an unbounded queue (for |
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* example a {@link LinkedBlockingQueue} without a predefined |
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* capacity) will cause new tasks to wait in the queue when all |
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* corePoolSize threads are busy. Thus, no more than corePoolSize |
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* threads will ever be created. (And the value of the maximumPoolSize |
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* therefore doesn't have any effect.) This may be appropriate when |
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* each task is completely independent of others, so tasks cannot |
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* affect each others execution; for example, in a web page server. |
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* While this style of queuing can be useful in smoothing out |
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* transient bursts of requests, it admits the possibility of |
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* unbounded work queue growth when commands continue to arrive on |
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* average faster than they can be processed. </li> |
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* |
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* <li><em>Bounded queues.</em> A bounded queue (for example, an |
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* {@link ArrayBlockingQueue}) helps prevent resource exhaustion when |
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* used with finite maximumPoolSizes, but can be more difficult to |
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* tune and control. Queue sizes and maximum pool sizes may be traded |
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* off for each other: Using large queues and small pools minimizes |
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* CPU usage, OS resources, and context-switching overhead, but can |
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* lead to artificially low throughput. If tasks frequently block (for |
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* example if they are I/O bound), a system may be able to schedule |
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* time for more threads than you otherwise allow. Use of small queues |
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* generally requires larger pool sizes, which keeps CPUs busier but |
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* may encounter unacceptable scheduling overhead, which also |
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* decreases throughput. </li> |
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* |
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* </ol> |
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* |
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* </dd> |
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* |
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* <dt>Rejected tasks</dt> |
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* |
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* <dd> New tasks submitted in method {@link #execute} will be |
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* <em>rejected</em> when the Executor has been shut down, and also |
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* when the Executor uses finite bounds for both maximum threads and |
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* work queue capacity, and is saturated. In either case, the {@code |
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* execute} method invokes the {@link |
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* RejectedExecutionHandler#rejectedExecution} method of its {@link |
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* RejectedExecutionHandler}. Four predefined handler policies are |
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* provided: |
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* |
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* <ol> |
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* |
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* <li> In the default {@link ThreadPoolExecutor.AbortPolicy}, the |
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* handler throws a runtime {@link RejectedExecutionException} upon |
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* rejection. </li> |
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* |
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* <li> In {@link ThreadPoolExecutor.CallerRunsPolicy}, the thread |
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* that invokes {@code execute} itself runs the task. This provides a |
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* simple feedback control mechanism that will slow down the rate that |
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* new tasks are submitted. </li> |
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* |
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* <li> In {@link ThreadPoolExecutor.DiscardPolicy}, a task that |
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* cannot be executed is simply dropped. </li> |
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* |
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* <li>In {@link ThreadPoolExecutor.DiscardOldestPolicy}, if the |
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* executor is not shut down, the task at the head of the work queue |
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* is dropped, and then execution is retried (which can fail again, |
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* causing this to be repeated.) </li> |
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* |
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* </ol> |
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* |
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* It is possible to define and use other kinds of {@link |
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* RejectedExecutionHandler} classes. Doing so requires some care |
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* especially when policies are designed to work only under particular |
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* capacity or queuing policies. </dd> |
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* |
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* <dt>Hook methods</dt> |
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* |
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* <dd>This class provides {@code protected} overridable {@link |
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* #beforeExecute} and {@link #afterExecute} methods that are called |
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* before and after execution of each task. These can be used to |
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* manipulate the execution environment; for example, reinitializing |
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* ThreadLocals, gathering statistics, or adding log |
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* entries. Additionally, method {@link #terminated} can be overridden |
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* to perform any special processing that needs to be done once the |
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* Executor has fully terminated. |
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* |
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* <p>If hook or callback methods throw exceptions, internal worker |
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* threads may in turn fail and abruptly terminate.</dd> |
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* |
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* <dt>Queue maintenance</dt> |
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* |
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* <dd> Method {@link #getQueue} allows access to the work queue for |
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* purposes of monitoring and debugging. Use of this method for any |
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* other purpose is strongly discouraged. Two supplied methods, |
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* {@link #remove} and {@link #purge} are available to assist in |
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* storage reclamation when large numbers of queued tasks become |
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* cancelled.</dd> |
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* |
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* <dt>Finalization</dt> |
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* |
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* <dd> A pool that is no longer referenced in a program <em>AND</em> |
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* has no remaining threads will be {@code shutdown} automatically. If |
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* you would like to ensure that unreferenced pools are reclaimed even |
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* if users forget to call {@link #shutdown}, then you must arrange |
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* that unused threads eventually die, by setting appropriate |
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* keep-alive times, using a lower bound of zero core threads and/or |
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* setting {@link #allowCoreThreadTimeOut(boolean)}. </dd> |
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* |
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* </dl> |
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* |
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* <p> <b>Extension example</b>. Most extensions of this class |
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* override one or more of the protected hook methods. For example, |
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* here is a subclass that adds a simple pause/resume feature: |
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* |
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* <pre> {@code |
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* class PausableThreadPoolExecutor extends ThreadPoolExecutor { |
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* private boolean isPaused; |
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* private ReentrantLock pauseLock = new ReentrantLock(); |
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* private Condition unpaused = pauseLock.newCondition(); |
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* |
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* public PausableThreadPoolExecutor(...) { super(...); } |
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* |
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* protected void beforeExecute(Thread t, Runnable r) { |
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* super.beforeExecute(t, r); |
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* pauseLock.lock(); |
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* try { |
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* while (isPaused) unpaused.await(); |
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* } catch (InterruptedException ie) { |
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* t.interrupt(); |
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* } finally { |
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* pauseLock.unlock(); |
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* } |
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* } |
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* |
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* public void pause() { |
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* pauseLock.lock(); |
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* try { |
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* isPaused = true; |
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* } finally { |
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* pauseLock.unlock(); |
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* } |
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* } |
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* |
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* public void resume() { |
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* pauseLock.lock(); |
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* try { |
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* isPaused = false; |
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* unpaused.signalAll(); |
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* } finally { |
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* pauseLock.unlock(); |
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* } |
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* } |
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* }}</pre> |
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* |
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* @since 1.5 |
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* @author Doug Lea |
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*/ |
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public class ThreadPoolExecutor extends AbstractExecutorService { |
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/** |
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* The main pool control state, ctl, is an atomic integer packing |
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* two conceptual fields |
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* workerCount, indicating the effective number of threads |
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* runState, indicating whether running, shutting down etc |
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* |
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* In order to pack them into one int, we limit workerCount to |
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* (2^29)-1 (about 500 million) threads rather than (2^31)-1 (2 |
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* billion) otherwise representable. If this is ever an issue in |
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* the future, the variable can be changed to be an AtomicLong, |
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* and the shift/mask constants below adjusted. But until the need |
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* arises, this code is a bit faster and simpler using an int. |
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* |
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* The workerCount is the number of workers that have been |
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* permitted to start and not permitted to stop. The value may be |
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* transiently different from the actual number of live threads, |
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* for example when a ThreadFactory fails to create a thread when |
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* asked, and when exiting threads are still performing |
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* bookkeeping before terminating. The user-visible pool size is |
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* reported as the current size of the workers set. |
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* |
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* The runState provides the main lifecyle control, taking on values: |
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* |
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* RUNNING: Accept new tasks and process queued tasks |
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* SHUTDOWN: Don't accept new tasks, but process queued tasks |
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* STOP: Don't accept new tasks, don't process queued tasks, |
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* and interrupt in-progress tasks |
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* TIDYING: All tasks have terminated, workerCount is zero, |
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* the thread transitioning to state TIDYING |
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* will run the terminated() hook method |
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* TERMINATED: terminated() has completed |
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* |
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* The numerical order among these values matters, to allow |
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* ordered comparisons. The runState monotonically increases over |
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* time, but need not hit each state. The transitions are: |
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* |
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* RUNNING -> SHUTDOWN |
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* On invocation of shutdown(), perhaps implicitly in finalize() |
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* (RUNNING or SHUTDOWN) -> STOP |
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* On invocation of shutdownNow() |
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* SHUTDOWN -> TIDYING |
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* When both queue and pool are empty |
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* STOP -> TIDYING |
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* When pool is empty |
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* TIDYING -> TERMINATED |
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* When the terminated() hook method has completed |
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* |
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* Threads waiting in awaitTermination() will return when the |
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* state reaches TERMINATED. |
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* |
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* Detecting the transition from SHUTDOWN to TIDYING is less |
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* straightforward than you'd like because the queue may become |
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* empty after non-empty and vice versa during SHUTDOWN state, but |
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* we can only terminate if, after seeing that it is empty, we see |
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* that workerCount is 0 (which sometimes entails a recheck -- see |
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* below). |
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*/ |
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private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0)); |
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private static final int COUNT_BITS = Integer.SIZE - 3; |
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private static final int CAPACITY = (1 << COUNT_BITS) - 1; |
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// runState is stored in the high-order bits |
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private static final int RUNNING = -1 << COUNT_BITS; |
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private static final int SHUTDOWN = 0 << COUNT_BITS; |
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private static final int STOP = 1 << COUNT_BITS; |
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private static final int TIDYING = 2 << COUNT_BITS; |
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private static final int TERMINATED = 3 << COUNT_BITS; |
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// Packing and unpacking ctl |
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private static int runStateOf(int c) { return c & ~CAPACITY; } |
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private static int workerCountOf(int c) { return c & CAPACITY; } |
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private static int ctlOf(int rs, int wc) { return rs | wc; } |
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/* |
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* Bit field accessors that don't require unpacking ctl. |
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* These depend on the bit layout and on workerCount being never negative. |
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*/ |
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private static boolean runStateLessThan(int c, int s) { |
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return c < s; |
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} |
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private static boolean runStateAtLeast(int c, int s) { |
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return c >= s; |
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} |
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private static boolean isRunning(int c) { |
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return c < SHUTDOWN; |
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} |
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/** |
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* Attempt to CAS-increment the workerCount field of ctl. |
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*/ |
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private boolean compareAndIncrementWorkerCount(int expect) { |
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return ctl.compareAndSet(expect, expect + 1); |
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} |
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/** |
|
414 |
* Attempt to CAS-decrement the workerCount field of ctl. |
|
415 |
*/ |
|
416 |
private boolean compareAndDecrementWorkerCount(int expect) { |
|
417 |
return ctl.compareAndSet(expect, expect - 1); |
|
418 |
} |
|
419 |
||
420 |
/** |
|
421 |
* Decrements the workerCount field of ctl. This is called only on |
|
422 |
* abrupt termination of a thread (see processWorkerExit). Other |
|
423 |
* decrements are performed within getTask. |
|
424 |
*/ |
|
425 |
private void decrementWorkerCount() { |
|
426 |
do {} while (! compareAndDecrementWorkerCount(ctl.get())); |
|
427 |
} |
|
428 |
||
429 |
/** |
|
430 |
* The queue used for holding tasks and handing off to worker |
|
431 |
* threads. We do not require that workQueue.poll() returning |
|
432 |
* null necessarily means that workQueue.isEmpty(), so rely |
|
433 |
* solely on isEmpty to see if the queue is empty (which we must |
|
434 |
* do for example when deciding whether to transition from |
|
435 |
* SHUTDOWN to TIDYING). This accommodates special-purpose |
|
436 |
* queues such as DelayQueues for which poll() is allowed to |
|
437 |
* return null even if it may later return non-null when delays |
|
438 |
* expire. |
|
439 |
*/ |
|
440 |
private final BlockingQueue<Runnable> workQueue; |
|
441 |
||
442 |
/** |
|
443 |
* Lock held on access to workers set and related bookkeeping. |
|
444 |
* While we could use a concurrent set of some sort, it turns out |
|
445 |
* to be generally preferable to use a lock. Among the reasons is |
|
446 |
* that this serializes interruptIdleWorkers, which avoids |
|
447 |
* unnecessary interrupt storms, especially during shutdown. |
|
448 |
* Otherwise exiting threads would concurrently interrupt those |
|
449 |
* that have not yet interrupted. It also simplifies some of the |
|
450 |
* associated statistics bookkeeping of largestPoolSize etc. We |
|
451 |
* also hold mainLock on shutdown and shutdownNow, for the sake of |
|
452 |
* ensuring workers set is stable while separately checking |
|
453 |
* permission to interrupt and actually interrupting. |
|
454 |
*/ |
|
455 |
private final ReentrantLock mainLock = new ReentrantLock(); |
|
456 |
||
457 |
/** |
|
458 |
* Set containing all worker threads in pool. Accessed only when |
|
459 |
* holding mainLock. |
|
460 |
*/ |
|
461 |
private final HashSet<Worker> workers = new HashSet<Worker>(); |
|
462 |
||
463 |
/** |
|
464 |
* Wait condition to support awaitTermination |
|
465 |
*/ |
|
466 |
private final Condition termination = mainLock.newCondition(); |
|
467 |
||
468 |
/** |
|
469 |
* Tracks largest attained pool size. Accessed only under |
|
470 |
* mainLock. |
|
471 |
*/ |
|
472 |
private int largestPoolSize; |
|
473 |
||
474 |
/** |
|
475 |
* Counter for completed tasks. Updated only on termination of |
|
476 |
* worker threads. Accessed only under mainLock. |
|
477 |
*/ |
|
478 |
private long completedTaskCount; |
|
479 |
||
480 |
/* |
|
481 |
* All user control parameters are declared as volatiles so that |
|
482 |
* ongoing actions are based on freshest values, but without need |
|
483 |
* for locking, since no internal invariants depend on them |
|
484 |
* changing synchronously with respect to other actions. |
|
485 |
*/ |
|
486 |
||
487 |
/** |
|
488 |
* Factory for new threads. All threads are created using this |
|
489 |
* factory (via method addWorker). All callers must be prepared |
|
490 |
* for addWorker to fail, which may reflect a system or user's |
|
491 |
* policy limiting the number of threads. Even though it is not |
|
492 |
* treated as an error, failure to create threads may result in |
|
493 |
* new tasks being rejected or existing ones remaining stuck in |
|
494 |
* the queue. On the other hand, no special precautions exist to |
|
495 |
* handle OutOfMemoryErrors that might be thrown while trying to |
|
496 |
* create threads, since there is generally no recourse from |
|
497 |
* within this class. |
|
498 |
*/ |
|
499 |
private volatile ThreadFactory threadFactory; |
|
500 |
||
501 |
/** |
|
502 |
* Handler called when saturated or shutdown in execute. |
|
503 |
*/ |
|
504 |
private volatile RejectedExecutionHandler handler; |
|
505 |
||
506 |
/** |
|
507 |
* Timeout in nanoseconds for idle threads waiting for work. |
|
508 |
* Threads use this timeout when there are more than corePoolSize |
|
509 |
* present or if allowCoreThreadTimeOut. Otherwise they wait |
|
510 |
* forever for new work. |
|
511 |
*/ |
|
512 |
private volatile long keepAliveTime; |
|
513 |
||
514 |
/** |
|
515 |
* If false (default), core threads stay alive even when idle. |
|
516 |
* If true, core threads use keepAliveTime to time out waiting |
|
517 |
* for work. |
|
518 |
*/ |
|
519 |
private volatile boolean allowCoreThreadTimeOut; |
|
520 |
||
521 |
/** |
|
522 |
* Core pool size is the minimum number of workers to keep alive |
|
523 |
* (and not allow to time out etc) unless allowCoreThreadTimeOut |
|
524 |
* is set, in which case the minimum is zero. |
|
525 |
*/ |
|
526 |
private volatile int corePoolSize; |
|
527 |
||
528 |
/** |
|
529 |
* Maximum pool size. Note that the actual maximum is internally |
|
530 |
* bounded by CAPACITY. |
|
531 |
*/ |
|
532 |
private volatile int maximumPoolSize; |
|
533 |
||
534 |
/** |
|
535 |
* The default rejected execution handler |
|
536 |
*/ |
|
537 |
private static final RejectedExecutionHandler defaultHandler = |
|
538 |
new AbortPolicy(); |
|
539 |
||
540 |
/** |
|
541 |
* Permission required for callers of shutdown and shutdownNow. |
|
542 |
* We additionally require (see checkShutdownAccess) that callers |
|
543 |
* have permission to actually interrupt threads in the worker set |
|
544 |
* (as governed by Thread.interrupt, which relies on |
|
545 |
* ThreadGroup.checkAccess, which in turn relies on |
|
546 |
* SecurityManager.checkAccess). Shutdowns are attempted only if |
|
547 |
* these checks pass. |
|
548 |
* |
|
549 |
* All actual invocations of Thread.interrupt (see |
|
550 |
* interruptIdleWorkers and interruptWorkers) ignore |
|
551 |
* SecurityExceptions, meaning that the attempted interrupts |
|
552 |
* silently fail. In the case of shutdown, they should not fail |
|
553 |
* unless the SecurityManager has inconsistent policies, sometimes |
|
554 |
* allowing access to a thread and sometimes not. In such cases, |
|
555 |
* failure to actually interrupt threads may disable or delay full |
|
556 |
* termination. Other uses of interruptIdleWorkers are advisory, |
|
557 |
* and failure to actually interrupt will merely delay response to |
|
558 |
* configuration changes so is not handled exceptionally. |
|
559 |
*/ |
|
560 |
private static final RuntimePermission shutdownPerm = |
|
561 |
new RuntimePermission("modifyThread"); |
|
562 |
||
563 |
/** |
|
564 |
* Class Worker mainly maintains interrupt control state for |
|
565 |
* threads running tasks, along with other minor bookkeeping. |
|
566 |
* This class opportunistically extends AbstractQueuedSynchronizer |
|
567 |
* to simplify acquiring and releasing a lock surrounding each |
|
568 |
* task execution. This protects against interrupts that are |
|
569 |
* intended to wake up a worker thread waiting for a task from |
|
570 |
* instead interrupting a task being run. We implement a simple |
|
571 |
* non-reentrant mutual exclusion lock rather than use ReentrantLock |
|
572 |
* because we do not want worker tasks to be able to reacquire the |
|
573 |
* lock when they invoke pool control methods like setCorePoolSize. |
|
574 |
*/ |
|
575 |
private final class Worker |
|
576 |
extends AbstractQueuedSynchronizer |
|
577 |
implements Runnable |
|
578 |
{ |
|
579 |
/** |
|
580 |
* This class will never be serialized, but we provide a |
|
581 |
* serialVersionUID to suppress a javac warning. |
|
582 |
*/ |
|
583 |
private static final long serialVersionUID = 6138294804551838833L; |
|
584 |
||
585 |
/** Thread this worker is running in. Null if factory fails. */ |
|
586 |
final Thread thread; |
|
587 |
/** Initial task to run. Possibly null. */ |
|
588 |
Runnable firstTask; |
|
589 |
/** Per-thread task counter */ |
|
590 |
volatile long completedTasks; |
|
591 |
||
592 |
/** |
|
593 |
* Creates with given first task and thread from ThreadFactory. |
|
594 |
* @param firstTask the first task (null if none) |
|
595 |
*/ |
|
596 |
Worker(Runnable firstTask) { |
|
597 |
this.firstTask = firstTask; |
|
598 |
this.thread = getThreadFactory().newThread(this); |
|
599 |
} |
|
600 |
||
601 |
/** Delegates main run loop to outer runWorker */ |
|
602 |
public void run() { |
|
603 |
runWorker(this); |
|
604 |
} |
|
605 |
||
606 |
// Lock methods |
|
607 |
// |
|
608 |
// The value 0 represents the unlocked state. |
|
609 |
// The value 1 represents the locked state. |
|
610 |
||
611 |
protected boolean isHeldExclusively() { |
|
612 |
return getState() == 1; |
|
613 |
} |
|
614 |
||
615 |
protected boolean tryAcquire(int unused) { |
|
616 |
if (compareAndSetState(0, 1)) { |
|
617 |
setExclusiveOwnerThread(Thread.currentThread()); |
|
618 |
return true; |
|
619 |
} |
|
620 |
return false; |
|
621 |
} |
|
622 |
||
623 |
protected boolean tryRelease(int unused) { |
|
624 |
setExclusiveOwnerThread(null); |
|
625 |
setState(0); |
|
626 |
return true; |
|
627 |
} |
|
628 |
||
629 |
public void lock() { acquire(1); } |
|
630 |
public boolean tryLock() { return tryAcquire(1); } |
|
631 |
public void unlock() { release(1); } |
|
632 |
public boolean isLocked() { return isHeldExclusively(); } |
|
633 |
} |
|
634 |
||
635 |
/* |
|
636 |
* Methods for setting control state |
|
637 |
*/ |
|
638 |
||
639 |
/** |
|
640 |
* Transitions runState to given target, or leaves it alone if |
|
641 |
* already at least the given target. |
|
642 |
* |
|
643 |
* @param targetState the desired state, either SHUTDOWN or STOP |
|
644 |
* (but not TIDYING or TERMINATED -- use tryTerminate for that) |
|
645 |
*/ |
|
646 |
private void advanceRunState(int targetState) { |
|
647 |
for (;;) { |
|
648 |
int c = ctl.get(); |
|
649 |
if (runStateAtLeast(c, targetState) || |
|
650 |
ctl.compareAndSet(c, ctlOf(targetState, workerCountOf(c)))) |
|
651 |
break; |
|
652 |
} |
|
653 |
} |
|
654 |
||
655 |
/** |
|
656 |
* Transitions to TERMINATED state if either (SHUTDOWN and pool |
|
657 |
* and queue empty) or (STOP and pool empty). If otherwise |
|
658 |
* eligible to terminate but workerCount is nonzero, interrupts an |
|
659 |
* idle worker to ensure that shutdown signals propagate. This |
|
660 |
* method must be called following any action that might make |
|
661 |
* termination possible -- reducing worker count or removing tasks |
|
662 |
* from the queue during shutdown. The method is non-private to |
|
663 |
* allow access from ScheduledThreadPoolExecutor. |
|
664 |
*/ |
|
665 |
final void tryTerminate() { |
|
666 |
for (;;) { |
|
667 |
int c = ctl.get(); |
|
668 |
if (isRunning(c) || |
|
669 |
runStateAtLeast(c, TIDYING) || |
|
670 |
(runStateOf(c) == SHUTDOWN && ! workQueue.isEmpty())) |
|
671 |
return; |
|
672 |
if (workerCountOf(c) != 0) { // Eligible to terminate |
|
673 |
interruptIdleWorkers(ONLY_ONE); |
|
674 |
return; |
|
675 |
} |
|
676 |
||
677 |
final ReentrantLock mainLock = this.mainLock; |
|
678 |
mainLock.lock(); |
|
679 |
try { |
|
680 |
if (ctl.compareAndSet(c, ctlOf(TIDYING, 0))) { |
|
681 |
try { |
|
682 |
terminated(); |
|
683 |
} finally { |
|
684 |
ctl.set(ctlOf(TERMINATED, 0)); |
|
685 |
termination.signalAll(); |
|
686 |
} |
|
687 |
return; |
|
688 |
} |
|
689 |
} finally { |
|
690 |
mainLock.unlock(); |
|
691 |
} |
|
692 |
// else retry on failed CAS |
|
693 |
} |
|
694 |
} |
|
695 |
||
696 |
/* |
|
697 |
* Methods for controlling interrupts to worker threads. |
|
698 |
*/ |
|
699 |
||
700 |
/** |
|
701 |
* If there is a security manager, makes sure caller has |
|
702 |
* permission to shut down threads in general (see shutdownPerm). |
|
703 |
* If this passes, additionally makes sure the caller is allowed |
|
704 |
* to interrupt each worker thread. This might not be true even if |
|
705 |
* first check passed, if the SecurityManager treats some threads |
|
706 |
* specially. |
|
707 |
*/ |
|
708 |
private void checkShutdownAccess() { |
|
709 |
SecurityManager security = System.getSecurityManager(); |
|
710 |
if (security != null) { |
|
711 |
security.checkPermission(shutdownPerm); |
|
712 |
final ReentrantLock mainLock = this.mainLock; |
|
713 |
mainLock.lock(); |
|
714 |
try { |
|
715 |
for (Worker w : workers) |
|
716 |
security.checkAccess(w.thread); |
|
717 |
} finally { |
|
718 |
mainLock.unlock(); |
|
719 |
} |
|
720 |
} |
|
721 |
} |
|
722 |
||
723 |
/** |
|
724 |
* Interrupts all threads, even if active. Ignores SecurityExceptions |
|
725 |
* (in which case some threads may remain uninterrupted). |
|
726 |
*/ |
|
727 |
private void interruptWorkers() { |
|
728 |
final ReentrantLock mainLock = this.mainLock; |
|
729 |
mainLock.lock(); |
|
730 |
try { |
|
731 |
for (Worker w : workers) { |
|
732 |
try { |
|
733 |
w.thread.interrupt(); |
|
734 |
} catch (SecurityException ignore) { |
|
735 |
} |
|
736 |
} |
|
737 |
} finally { |
|
738 |
mainLock.unlock(); |
|
739 |
} |
|
740 |
} |
|
741 |
||
742 |
/** |
|
743 |
* Interrupts threads that might be waiting for tasks (as |
|
744 |
* indicated by not being locked) so they can check for |
|
745 |
* termination or configuration changes. Ignores |
|
746 |
* SecurityExceptions (in which case some threads may remain |
|
747 |
* uninterrupted). |
|
748 |
* |
|
749 |
* @param onlyOne If true, interrupt at most one worker. This is |
|
750 |
* called only from tryTerminate when termination is otherwise |
|
751 |
* enabled but there are still other workers. In this case, at |
|
752 |
* most one waiting worker is interrupted to propagate shutdown |
|
753 |
* signals in case all threads are currently waiting. |
|
754 |
* Interrupting any arbitrary thread ensures that newly arriving |
|
755 |
* workers since shutdown began will also eventually exit. |
|
756 |
* To guarantee eventual termination, it suffices to always |
|
757 |
* interrupt only one idle worker, but shutdown() interrupts all |
|
758 |
* idle workers so that redundant workers exit promptly, not |
|
759 |
* waiting for a straggler task to finish. |
|
760 |
*/ |
|
761 |
private void interruptIdleWorkers(boolean onlyOne) { |
|
762 |
final ReentrantLock mainLock = this.mainLock; |
|
763 |
mainLock.lock(); |
|
764 |
try { |
|
765 |
for (Worker w : workers) { |
|
766 |
Thread t = w.thread; |
|
767 |
if (!t.isInterrupted() && w.tryLock()) { |
|
768 |
try { |
|
769 |
t.interrupt(); |
|
770 |
} catch (SecurityException ignore) { |
|
771 |
} finally { |
|
772 |
w.unlock(); |
|
773 |
} |
|
774 |
} |
|
775 |
if (onlyOne) |
|
776 |
break; |
|
777 |
} |
|
778 |
} finally { |
|
779 |
mainLock.unlock(); |
|
780 |
} |
|
781 |
} |
|
782 |
||
783 |
/** |
|
784 |
* Common form of interruptIdleWorkers, to avoid having to |
|
785 |
* remember what the boolean argument means. |
|
786 |
*/ |
|
787 |
private void interruptIdleWorkers() { |
|
788 |
interruptIdleWorkers(false); |
|
789 |
} |
|
790 |
||
791 |
private static final boolean ONLY_ONE = true; |
|
792 |
||
793 |
/** |
|
794 |
* Ensures that unless the pool is stopping, the current thread |
|
795 |
* does not have its interrupt set. This requires a double-check |
|
796 |
* of state in case the interrupt was cleared concurrently with a |
|
797 |
* shutdownNow -- if so, the interrupt is re-enabled. |
|
798 |
*/ |
|
799 |
private void clearInterruptsForTaskRun() { |
|
800 |
if (runStateLessThan(ctl.get(), STOP) && |
|
801 |
Thread.interrupted() && |
|
802 |
runStateAtLeast(ctl.get(), STOP)) |
|
803 |
Thread.currentThread().interrupt(); |
|
804 |
} |
|
805 |
||
806 |
/* |
|
807 |
* Misc utilities, most of which are also exported to |
|
808 |
* ScheduledThreadPoolExecutor |
|
809 |
*/ |
|
810 |
||
811 |
/** |
|
812 |
* Invokes the rejected execution handler for the given command. |
|
813 |
* Package-protected for use by ScheduledThreadPoolExecutor. |
|
814 |
*/ |
|
815 |
final void reject(Runnable command) { |
|
816 |
handler.rejectedExecution(command, this); |
|
817 |
} |
|
818 |
||
819 |
/** |
|
820 |
* Performs any further cleanup following run state transition on |
|
821 |
* invocation of shutdown. A no-op here, but used by |
|
822 |
* ScheduledThreadPoolExecutor to cancel delayed tasks. |
|
823 |
*/ |
|
824 |
void onShutdown() { |
|
825 |
} |
|
826 |
||
827 |
/** |
|
828 |
* State check needed by ScheduledThreadPoolExecutor to |
|
829 |
* enable running tasks during shutdown. |
|
830 |
* |
|
831 |
* @param shutdownOK true if should return true if SHUTDOWN |
|
832 |
*/ |
|
833 |
final boolean isRunningOrShutdown(boolean shutdownOK) { |
|
834 |
int rs = runStateOf(ctl.get()); |
|
835 |
return rs == RUNNING || (rs == SHUTDOWN && shutdownOK); |
|
836 |
} |
|
837 |
||
838 |
/** |
|
839 |
* Drains the task queue into a new list, normally using |
|
840 |
* drainTo. But if the queue is a DelayQueue or any other kind of |
|
841 |
* queue for which poll or drainTo may fail to remove some |
|
842 |
* elements, it deletes them one by one. |
|
843 |
*/ |
|
844 |
private List<Runnable> drainQueue() { |
|
845 |
BlockingQueue<Runnable> q = workQueue; |
|
846 |
List<Runnable> taskList = new ArrayList<Runnable>(); |
|
847 |
q.drainTo(taskList); |
|
848 |
if (!q.isEmpty()) { |
|
849 |
for (Runnable r : q.toArray(new Runnable[0])) { |
|
850 |
if (q.remove(r)) |
|
851 |
taskList.add(r); |
|
852 |
} |
|
853 |
} |
|
854 |
return taskList; |
|
855 |
} |
|
856 |
||
857 |
/* |
|
858 |
* Methods for creating, running and cleaning up after workers |
|
859 |
*/ |
|
860 |
||
861 |
/** |
|
862 |
* Checks if a new worker can be added with respect to current |
|
863 |
* pool state and the given bound (either core or maximum). If so, |
|
864 |
* the worker count is adjusted accordingly, and, if possible, a |
|
865 |
* new worker is created and started running firstTask as its |
|
866 |
* first task. This method returns false if the pool is stopped or |
|
867 |
* eligible to shut down. It also returns false if the thread |
|
868 |
* factory fails to create a thread when asked, which requires a |
|
869 |
* backout of workerCount, and a recheck for termination, in case |
|
870 |
* the existence of this worker was holding up termination. |
|
871 |
* |
|
872 |
* @param firstTask the task the new thread should run first (or |
|
873 |
* null if none). Workers are created with an initial first task |
|
874 |
* (in method execute()) to bypass queuing when there are fewer |
|
875 |
* than corePoolSize threads (in which case we always start one), |
|
876 |
* or when the queue is full (in which case we must bypass queue). |
|
877 |
* Initially idle threads are usually created via |
|
878 |
* prestartCoreThread or to replace other dying workers. |
|
879 |
* |
|
880 |
* @param core if true use corePoolSize as bound, else |
|
881 |
* maximumPoolSize. (A boolean indicator is used here rather than a |
|
882 |
* value to ensure reads of fresh values after checking other pool |
|
883 |
* state). |
|
884 |
* @return true if successful |
|
885 |
*/ |
|
886 |
private boolean addWorker(Runnable firstTask, boolean core) { |
|
887 |
retry: |
|
888 |
for (;;) { |
|
889 |
int c = ctl.get(); |
|
890 |
int rs = runStateOf(c); |
|
891 |
||
892 |
// Check if queue empty only if necessary. |
|
893 |
if (rs >= SHUTDOWN && |
|
894 |
! (rs == SHUTDOWN && |
|
895 |
firstTask == null && |
|
896 |
! workQueue.isEmpty())) |
|
897 |
return false; |
|
898 |
||
899 |
for (;;) { |
|
900 |
int wc = workerCountOf(c); |
|
901 |
if (wc >= CAPACITY || |
|
902 |
wc >= (core ? corePoolSize : maximumPoolSize)) |
|
903 |
return false; |
|
904 |
if (compareAndIncrementWorkerCount(c)) |
|
905 |
break retry; |
|
906 |
c = ctl.get(); // Re-read ctl |
|
907 |
if (runStateOf(c) != rs) |
|
908 |
continue retry; |
|
909 |
// else CAS failed due to workerCount change; retry inner loop |
|
910 |
} |
|
911 |
} |
|
912 |
||
913 |
Worker w = new Worker(firstTask); |
|
914 |
Thread t = w.thread; |
|
915 |
||
916 |
final ReentrantLock mainLock = this.mainLock; |
|
917 |
mainLock.lock(); |
|
918 |
try { |
|
919 |
// Recheck while holding lock. |
|
920 |
// Back out on ThreadFactory failure or if |
|
921 |
// shut down before lock acquired. |
|
922 |
int c = ctl.get(); |
|
923 |
int rs = runStateOf(c); |
|
924 |
||
925 |
if (t == null || |
|
926 |
(rs >= SHUTDOWN && |
|
927 |
! (rs == SHUTDOWN && |
|
928 |
firstTask == null))) { |
|
929 |
decrementWorkerCount(); |
|
930 |
tryTerminate(); |
|
931 |
return false; |
|
932 |
} |
|
933 |
||
934 |
workers.add(w); |
|
935 |
||
936 |
int s = workers.size(); |
|
937 |
if (s > largestPoolSize) |
|
938 |
largestPoolSize = s; |
|
939 |
} finally { |
|
940 |
mainLock.unlock(); |
|
941 |
} |
|
942 |
||
943 |
t.start(); |
|
944 |
// It is possible (but unlikely) for a thread to have been |
|
945 |
// added to workers, but not yet started, during transition to |
|
946 |
// STOP, which could result in a rare missed interrupt, |
|
947 |
// because Thread.interrupt is not guaranteed to have any effect |
|
948 |
// on a non-yet-started Thread (see Thread#interrupt). |
|
949 |
if (runStateOf(ctl.get()) == STOP && ! t.isInterrupted()) |
|
950 |
t.interrupt(); |
|
951 |
||
952 |
return true; |
|
953 |
} |
|
954 |
||
955 |
/** |
|
956 |
* Performs cleanup and bookkeeping for a dying worker. Called |
|
957 |
* only from worker threads. Unless completedAbruptly is set, |
|
958 |
* assumes that workerCount has already been adjusted to account |
|
959 |
* for exit. This method removes thread from worker set, and |
|
960 |
* possibly terminates the pool or replaces the worker if either |
|
961 |
* it exited due to user task exception or if fewer than |
|
962 |
* corePoolSize workers are running or queue is non-empty but |
|
963 |
* there are no workers. |
|
964 |
* |
|
965 |
* @param w the worker |
|
966 |
* @param completedAbruptly if the worker died due to user exception |
|
967 |
*/ |
|
968 |
private void processWorkerExit(Worker w, boolean completedAbruptly) { |
|
969 |
if (completedAbruptly) // If abrupt, then workerCount wasn't adjusted |
|
970 |
decrementWorkerCount(); |
|
971 |
||
972 |
final ReentrantLock mainLock = this.mainLock; |
|
973 |
mainLock.lock(); |
|
974 |
try { |
|
975 |
completedTaskCount += w.completedTasks; |
|
976 |
workers.remove(w); |
|
977 |
} finally { |
|
978 |
mainLock.unlock(); |
|
979 |
} |
|
980 |
||
981 |
tryTerminate(); |
|
982 |
||
983 |
int c = ctl.get(); |
|
984 |
if (runStateLessThan(c, STOP)) { |
|
985 |
if (!completedAbruptly) { |
|
986 |
int min = allowCoreThreadTimeOut ? 0 : corePoolSize; |
|
987 |
if (min == 0 && ! workQueue.isEmpty()) |
|
988 |
min = 1; |
|
989 |
if (workerCountOf(c) >= min) |
|
990 |
return; // replacement not needed |
|
991 |
} |
|
992 |
addWorker(null, false); |
|
993 |
} |
|
994 |
} |
|
995 |
||
996 |
/** |
|
997 |
* Performs blocking or timed wait for a task, depending on |
|
998 |
* current configuration settings, or returns null if this worker |
|
999 |
* must exit because of any of: |
|
1000 |
* 1. There are more than maximumPoolSize workers (due to |
|
1001 |
* a call to setMaximumPoolSize). |
|
1002 |
* 2. The pool is stopped. |
|
1003 |
* 3. The pool is shutdown and the queue is empty. |
|
1004 |
* 4. This worker timed out waiting for a task, and timed-out |
|
1005 |
* workers are subject to termination (that is, |
|
1006 |
* {@code allowCoreThreadTimeOut || workerCount > corePoolSize}) |
|
1007 |
* both before and after the timed wait. |
|
1008 |
* |
|
1009 |
* @return task, or null if the worker must exit, in which case |
|
1010 |
* workerCount is decremented |
|
1011 |
*/ |
|
1012 |
private Runnable getTask() { |
|
1013 |
boolean timedOut = false; // Did the last poll() time out? |
|
1014 |
||
1015 |
retry: |
|
1016 |
for (;;) { |
|
1017 |
int c = ctl.get(); |
|
1018 |
int rs = runStateOf(c); |
|
1019 |
||
1020 |
// Check if queue empty only if necessary. |
|
1021 |
if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) { |
|
1022 |
decrementWorkerCount(); |
|
1023 |
return null; |
|
1024 |
} |
|
1025 |
||
1026 |
boolean timed; // Are workers subject to culling? |
|
1027 |
||
1028 |
for (;;) { |
|
1029 |
int wc = workerCountOf(c); |
|
1030 |
timed = allowCoreThreadTimeOut || wc > corePoolSize; |
|
1031 |
||
1032 |
if (wc <= maximumPoolSize && ! (timedOut && timed)) |
|
1033 |
break; |
|
1034 |
if (compareAndDecrementWorkerCount(c)) |
|
1035 |
return null; |
|
1036 |
c = ctl.get(); // Re-read ctl |
|
1037 |
if (runStateOf(c) != rs) |
|
1038 |
continue retry; |
|
1039 |
// else CAS failed due to workerCount change; retry inner loop |
|
1040 |
} |
|
1041 |
||
1042 |
try { |
|
1043 |
Runnable r = timed ? |
|
1044 |
workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) : |
|
1045 |
workQueue.take(); |
|
1046 |
if (r != null) |
|
1047 |
return r; |
|
1048 |
timedOut = true; |
|
1049 |
} catch (InterruptedException retry) { |
|
1050 |
timedOut = false; |
|
1051 |
} |
|
1052 |
} |
|
1053 |
} |
|
1054 |
||
1055 |
/** |
|
1056 |
* Main worker run loop. Repeatedly gets tasks from queue and |
|
1057 |
* executes them, while coping with a number of issues: |
|
1058 |
* |
|
1059 |
* 1. We may start out with an initial task, in which case we |
|
1060 |
* don't need to get the first one. Otherwise, as long as pool is |
|
1061 |
* running, we get tasks from getTask. If it returns null then the |
|
1062 |
* worker exits due to changed pool state or configuration |
|
1063 |
* parameters. Other exits result from exception throws in |
|
1064 |
* external code, in which case completedAbruptly holds, which |
|
1065 |
* usually leads processWorkerExit to replace this thread. |
|
1066 |
* |
|
1067 |
* 2. Before running any task, the lock is acquired to prevent |
|
1068 |
* other pool interrupts while the task is executing, and |
|
1069 |
* clearInterruptsForTaskRun called to ensure that unless pool is |
|
1070 |
* stopping, this thread does not have its interrupt set. |
|
1071 |
* |
|
1072 |
* 3. Each task run is preceded by a call to beforeExecute, which |
|
1073 |
* might throw an exception, in which case we cause thread to die |
|
1074 |
* (breaking loop with completedAbruptly true) without processing |
|
1075 |
* the task. |
|
1076 |
* |
|
1077 |
* 4. Assuming beforeExecute completes normally, we run the task, |
|
1078 |
* gathering any of its thrown exceptions to send to |
|
1079 |
* afterExecute. We separately handle RuntimeException, Error |
|
1080 |
* (both of which the specs guarantee that we trap) and arbitrary |
|
1081 |
* Throwables. Because we cannot rethrow Throwables within |
|
1082 |
* Runnable.run, we wrap them within Errors on the way out (to the |
|
1083 |
* thread's UncaughtExceptionHandler). Any thrown exception also |
|
1084 |
* conservatively causes thread to die. |
|
1085 |
* |
|
1086 |
* 5. After task.run completes, we call afterExecute, which may |
|
1087 |
* also throw an exception, which will also cause thread to |
|
1088 |
* die. According to JLS Sec 14.20, this exception is the one that |
|
1089 |
* will be in effect even if task.run throws. |
|
1090 |
* |
|
1091 |
* The net effect of the exception mechanics is that afterExecute |
|
1092 |
* and the thread's UncaughtExceptionHandler have as accurate |
|
1093 |
* information as we can provide about any problems encountered by |
|
1094 |
* user code. |
|
1095 |
* |
|
1096 |
* @param w the worker |
|
1097 |
*/ |
|
1098 |
final void runWorker(Worker w) { |
|
1099 |
Runnable task = w.firstTask; |
|
1100 |
w.firstTask = null; |
|
1101 |
boolean completedAbruptly = true; |
|
1102 |
try { |
|
1103 |
while (task != null || (task = getTask()) != null) { |
|
1104 |
w.lock(); |
|
1105 |
clearInterruptsForTaskRun(); |
|
1106 |
try { |
|
1107 |
beforeExecute(w.thread, task); |
|
1108 |
Throwable thrown = null; |
|
1109 |
try { |
|
1110 |
task.run(); |
|
1111 |
} catch (RuntimeException x) { |
|
1112 |
thrown = x; throw x; |
|
1113 |
} catch (Error x) { |
|
1114 |
thrown = x; throw x; |
|
1115 |
} catch (Throwable x) { |
|
1116 |
thrown = x; throw new Error(x); |
|
1117 |
} finally { |
|
1118 |
afterExecute(task, thrown); |
|
1119 |
} |
|
1120 |
} finally { |
|
1121 |
task = null; |
|
1122 |
w.completedTasks++; |
|
1123 |
w.unlock(); |
|
1124 |
} |
|
1125 |
} |
|
1126 |
completedAbruptly = false; |
|
1127 |
} finally { |
|
1128 |
processWorkerExit(w, completedAbruptly); |
|
1129 |
} |
|
1130 |
} |
|
1131 |
||
1132 |
// Public constructors and methods |
|
1133 |
||
1134 |
/** |
|
1135 |
* Creates a new {@code ThreadPoolExecutor} with the given initial |
|
1136 |
* parameters and default thread factory and rejected execution handler. |
|
1137 |
* It may be more convenient to use one of the {@link Executors} factory |
|
1138 |
* methods instead of this general purpose constructor. |
|
1139 |
* |
|
1140 |
* @param corePoolSize the number of threads to keep in the pool, even |
|
1141 |
* if they are idle, unless {@code allowCoreThreadTimeOut} is set |
|
1142 |
* @param maximumPoolSize the maximum number of threads to allow in the |
|
1143 |
* pool |
|
1144 |
* @param keepAliveTime when the number of threads is greater than |
|
1145 |
* the core, this is the maximum time that excess idle threads |
|
1146 |
* will wait for new tasks before terminating. |
|
1147 |
* @param unit the time unit for the {@code keepAliveTime} argument |
|
1148 |
* @param workQueue the queue to use for holding tasks before they are |
|
1149 |
* executed. This queue will hold only the {@code Runnable} |
|
1150 |
* tasks submitted by the {@code execute} method. |
|
1151 |
* @throws IllegalArgumentException if one of the following holds:<br> |
|
1152 |
* {@code corePoolSize < 0}<br> |
|
1153 |
* {@code keepAliveTime < 0}<br> |
|
1154 |
* {@code maximumPoolSize <= 0}<br> |
|
1155 |
* {@code maximumPoolSize < corePoolSize} |
|
1156 |
* @throws NullPointerException if {@code workQueue} is null |
|
1157 |
*/ |
|
1158 |
public ThreadPoolExecutor(int corePoolSize, |
|
1159 |
int maximumPoolSize, |
|
1160 |
long keepAliveTime, |
|
1161 |
TimeUnit unit, |
|
1162 |
BlockingQueue<Runnable> workQueue) { |
|
1163 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
|
1164 |
Executors.defaultThreadFactory(), defaultHandler); |
|
1165 |
} |
|
1166 |
||
1167 |
/** |
|
1168 |
* Creates a new {@code ThreadPoolExecutor} with the given initial |
|
1169 |
* parameters and default rejected execution handler. |
|
1170 |
* |
|
1171 |
* @param corePoolSize the number of threads to keep in the pool, even |
|
1172 |
* if they are idle, unless {@code allowCoreThreadTimeOut} is set |
|
1173 |
* @param maximumPoolSize the maximum number of threads to allow in the |
|
1174 |
* pool |
|
1175 |
* @param keepAliveTime when the number of threads is greater than |
|
1176 |
* the core, this is the maximum time that excess idle threads |
|
1177 |
* will wait for new tasks before terminating. |
|
1178 |
* @param unit the time unit for the {@code keepAliveTime} argument |
|
1179 |
* @param workQueue the queue to use for holding tasks before they are |
|
1180 |
* executed. This queue will hold only the {@code Runnable} |
|
1181 |
* tasks submitted by the {@code execute} method. |
|
1182 |
* @param threadFactory the factory to use when the executor |
|
1183 |
* creates a new thread |
|
1184 |
* @throws IllegalArgumentException if one of the following holds:<br> |
|
1185 |
* {@code corePoolSize < 0}<br> |
|
1186 |
* {@code keepAliveTime < 0}<br> |
|
1187 |
* {@code maximumPoolSize <= 0}<br> |
|
1188 |
* {@code maximumPoolSize < corePoolSize} |
|
1189 |
* @throws NullPointerException if {@code workQueue} |
|
1190 |
* or {@code threadFactory} is null |
|
1191 |
*/ |
|
1192 |
public ThreadPoolExecutor(int corePoolSize, |
|
1193 |
int maximumPoolSize, |
|
1194 |
long keepAliveTime, |
|
1195 |
TimeUnit unit, |
|
1196 |
BlockingQueue<Runnable> workQueue, |
|
1197 |
ThreadFactory threadFactory) { |
|
1198 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
|
1199 |
threadFactory, defaultHandler); |
|
1200 |
} |
|
1201 |
||
1202 |
/** |
|
1203 |
* Creates a new {@code ThreadPoolExecutor} with the given initial |
|
1204 |
* parameters and default thread factory. |
|
1205 |
* |
|
1206 |
* @param corePoolSize the number of threads to keep in the pool, even |
|
1207 |
* if they are idle, unless {@code allowCoreThreadTimeOut} is set |
|
1208 |
* @param maximumPoolSize the maximum number of threads to allow in the |
|
1209 |
* pool |
|
1210 |
* @param keepAliveTime when the number of threads is greater than |
|
1211 |
* the core, this is the maximum time that excess idle threads |
|
1212 |
* will wait for new tasks before terminating. |
|
1213 |
* @param unit the time unit for the {@code keepAliveTime} argument |
|
1214 |
* @param workQueue the queue to use for holding tasks before they are |
|
1215 |
* executed. This queue will hold only the {@code Runnable} |
|
1216 |
* tasks submitted by the {@code execute} method. |
|
1217 |
* @param handler the handler to use when execution is blocked |
|
1218 |
* because the thread bounds and queue capacities are reached |
|
1219 |
* @throws IllegalArgumentException if one of the following holds:<br> |
|
1220 |
* {@code corePoolSize < 0}<br> |
|
1221 |
* {@code keepAliveTime < 0}<br> |
|
1222 |
* {@code maximumPoolSize <= 0}<br> |
|
1223 |
* {@code maximumPoolSize < corePoolSize} |
|
1224 |
* @throws NullPointerException if {@code workQueue} |
|
1225 |
* or {@code handler} is null |
|
1226 |
*/ |
|
1227 |
public ThreadPoolExecutor(int corePoolSize, |
|
1228 |
int maximumPoolSize, |
|
1229 |
long keepAliveTime, |
|
1230 |
TimeUnit unit, |
|
1231 |
BlockingQueue<Runnable> workQueue, |
|
1232 |
RejectedExecutionHandler handler) { |
|
1233 |
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, |
|
1234 |
Executors.defaultThreadFactory(), handler); |
|
1235 |
} |
|
1236 |
||
1237 |
/** |
|
1238 |
* Creates a new {@code ThreadPoolExecutor} with the given initial |
|
1239 |
* parameters. |
|
1240 |
* |
|
1241 |
* @param corePoolSize the number of threads to keep in the pool, even |
|
1242 |
* if they are idle, unless {@code allowCoreThreadTimeOut} is set |
|
1243 |
* @param maximumPoolSize the maximum number of threads to allow in the |
|
1244 |
* pool |
|
1245 |
* @param keepAliveTime when the number of threads is greater than |
|
1246 |
* the core, this is the maximum time that excess idle threads |
|
1247 |
* will wait for new tasks before terminating. |
|
1248 |
* @param unit the time unit for the {@code keepAliveTime} argument |
|
1249 |
* @param workQueue the queue to use for holding tasks before they are |
|
1250 |
* executed. This queue will hold only the {@code Runnable} |
|
1251 |
* tasks submitted by the {@code execute} method. |
|
1252 |
* @param threadFactory the factory to use when the executor |
|
1253 |
* creates a new thread |
|
1254 |
* @param handler the handler to use when execution is blocked |
|
1255 |
* because the thread bounds and queue capacities are reached |
|
1256 |
* @throws IllegalArgumentException if one of the following holds:<br> |
|
1257 |
* {@code corePoolSize < 0}<br> |
|
1258 |
* {@code keepAliveTime < 0}<br> |
|
1259 |
* {@code maximumPoolSize <= 0}<br> |
|
1260 |
* {@code maximumPoolSize < corePoolSize} |
|
1261 |
* @throws NullPointerException if {@code workQueue} |
|
1262 |
* or {@code threadFactory} or {@code handler} is null |
|
1263 |
*/ |
|
1264 |
public ThreadPoolExecutor(int corePoolSize, |
|
1265 |
int maximumPoolSize, |
|
1266 |
long keepAliveTime, |
|
1267 |
TimeUnit unit, |
|
1268 |
BlockingQueue<Runnable> workQueue, |
|
1269 |
ThreadFactory threadFactory, |
|
1270 |
RejectedExecutionHandler handler) { |
|
1271 |
if (corePoolSize < 0 || |
|
1272 |
maximumPoolSize <= 0 || |
|
1273 |
maximumPoolSize < corePoolSize || |
|
1274 |
keepAliveTime < 0) |
|
1275 |
throw new IllegalArgumentException(); |
|
1276 |
if (workQueue == null || threadFactory == null || handler == null) |
|
1277 |
throw new NullPointerException(); |
|
1278 |
this.corePoolSize = corePoolSize; |
|
1279 |
this.maximumPoolSize = maximumPoolSize; |
|
1280 |
this.workQueue = workQueue; |
|
1281 |
this.keepAliveTime = unit.toNanos(keepAliveTime); |
|
1282 |
this.threadFactory = threadFactory; |
|
1283 |
this.handler = handler; |
|
1284 |
} |
|
1285 |
||
1286 |
/** |
|
1287 |
* Executes the given task sometime in the future. The task |
|
1288 |
* may execute in a new thread or in an existing pooled thread. |
|
1289 |
* |
|
1290 |
* If the task cannot be submitted for execution, either because this |
|
1291 |
* executor has been shutdown or because its capacity has been reached, |
|
1292 |
* the task is handled by the current {@code RejectedExecutionHandler}. |
|
1293 |
* |
|
1294 |
* @param command the task to execute |
|
1295 |
* @throws RejectedExecutionException at discretion of |
|
1296 |
* {@code RejectedExecutionHandler}, if the task |
|
1297 |
* cannot be accepted for execution |
|
1298 |
* @throws NullPointerException if {@code command} is null |
|
1299 |
*/ |
|
1300 |
public void execute(Runnable command) { |
|
1301 |
if (command == null) |
|
1302 |
throw new NullPointerException(); |
|
1303 |
/* |
|
1304 |
* Proceed in 3 steps: |
|
1305 |
* |
|
1306 |
* 1. If fewer than corePoolSize threads are running, try to |
|
1307 |
* start a new thread with the given command as its first |
|
1308 |
* task. The call to addWorker atomically checks runState and |
|
1309 |
* workerCount, and so prevents false alarms that would add |
|
1310 |
* threads when it shouldn't, by returning false. |
|
1311 |
* |
|
1312 |
* 2. If a task can be successfully queued, then we still need |
|
1313 |
* to double-check whether we should have added a thread |
|
1314 |
* (because existing ones died since last checking) or that |
|
1315 |
* the pool shut down since entry into this method. So we |
|
1316 |
* recheck state and if necessary roll back the enqueuing if |
|
1317 |
* stopped, or start a new thread if there are none. |
|
1318 |
* |
|
1319 |
* 3. If we cannot queue task, then we try to add a new |
|
1320 |
* thread. If it fails, we know we are shut down or saturated |
|
1321 |
* and so reject the task. |
|
1322 |
*/ |
|
1323 |
int c = ctl.get(); |
|
1324 |
if (workerCountOf(c) < corePoolSize) { |
|
1325 |
if (addWorker(command, true)) |
|
1326 |
return; |
|
1327 |
c = ctl.get(); |
|
1328 |
} |
|
1329 |
if (isRunning(c) && workQueue.offer(command)) { |
|
1330 |
int recheck = ctl.get(); |
|
1331 |
if (! isRunning(recheck) && remove(command)) |
|
1332 |
reject(command); |
|
1333 |
else if (workerCountOf(recheck) == 0) |
|
1334 |
addWorker(null, false); |
|
1335 |
} |
|
1336 |
else if (!addWorker(command, false)) |
|
1337 |
reject(command); |
|
1338 |
} |
|
1339 |
||
1340 |
/** |
|
1341 |
* Initiates an orderly shutdown in which previously submitted |
|
1342 |
* tasks are executed, but no new tasks will be accepted. |
|
1343 |
* Invocation has no additional effect if already shut down. |
|
1344 |
* |
|
61
5691b03db1ea
6620549: ExecutorService#shutdown should clearly state that it does not block
martin
parents:
2
diff
changeset
|
1345 |
* <p>This method does not wait for previously submitted tasks to |
5691b03db1ea
6620549: ExecutorService#shutdown should clearly state that it does not block
martin
parents:
2
diff
changeset
|
1346 |
* complete execution. Use {@link #awaitTermination awaitTermination} |
5691b03db1ea
6620549: ExecutorService#shutdown should clearly state that it does not block
martin
parents:
2
diff
changeset
|
1347 |
* to do that. |
5691b03db1ea
6620549: ExecutorService#shutdown should clearly state that it does not block
martin
parents:
2
diff
changeset
|
1348 |
* |
2 | 1349 |
* @throws SecurityException {@inheritDoc} |
1350 |
*/ |
|
1351 |
public void shutdown() { |
|
1352 |
final ReentrantLock mainLock = this.mainLock; |
|
1353 |
mainLock.lock(); |
|
1354 |
try { |
|
1355 |
checkShutdownAccess(); |
|
1356 |
advanceRunState(SHUTDOWN); |
|
1357 |
interruptIdleWorkers(); |
|
1358 |
onShutdown(); // hook for ScheduledThreadPoolExecutor |
|
1359 |
} finally { |
|
1360 |
mainLock.unlock(); |
|
1361 |
} |
|
1362 |
tryTerminate(); |
|
1363 |
} |
|
1364 |
||
1365 |
/** |
|
1366 |
* Attempts to stop all actively executing tasks, halts the |
|
1367 |
* processing of waiting tasks, and returns a list of the tasks |
|
1368 |
* that were awaiting execution. These tasks are drained (removed) |
|
1369 |
* from the task queue upon return from this method. |
|
1370 |
* |
|
61
5691b03db1ea
6620549: ExecutorService#shutdown should clearly state that it does not block
martin
parents:
2
diff
changeset
|
1371 |
* <p>This method does not wait for actively executing tasks to |
5691b03db1ea
6620549: ExecutorService#shutdown should clearly state that it does not block
martin
parents:
2
diff
changeset
|
1372 |
* terminate. Use {@link #awaitTermination awaitTermination} to |
5691b03db1ea
6620549: ExecutorService#shutdown should clearly state that it does not block
martin
parents:
2
diff
changeset
|
1373 |
* do that. |
5691b03db1ea
6620549: ExecutorService#shutdown should clearly state that it does not block
martin
parents:
2
diff
changeset
|
1374 |
* |
2 | 1375 |
* <p>There are no guarantees beyond best-effort attempts to stop |
1376 |
* processing actively executing tasks. This implementation |
|
1377 |
* cancels tasks via {@link Thread#interrupt}, so any task that |
|
1378 |
* fails to respond to interrupts may never terminate. |
|
1379 |
* |
|
1380 |
* @throws SecurityException {@inheritDoc} |
|
1381 |
*/ |
|
1382 |
public List<Runnable> shutdownNow() { |
|
1383 |
List<Runnable> tasks; |
|
1384 |
final ReentrantLock mainLock = this.mainLock; |
|
1385 |
mainLock.lock(); |
|
1386 |
try { |
|
1387 |
checkShutdownAccess(); |
|
1388 |
advanceRunState(STOP); |
|
1389 |
interruptWorkers(); |
|
1390 |
tasks = drainQueue(); |
|
1391 |
} finally { |
|
1392 |
mainLock.unlock(); |
|
1393 |
} |
|
1394 |
tryTerminate(); |
|
1395 |
return tasks; |
|
1396 |
} |
|
1397 |
||
1398 |
public boolean isShutdown() { |
|
1399 |
return ! isRunning(ctl.get()); |
|
1400 |
} |
|
1401 |
||
1402 |
/** |
|
1403 |
* Returns true if this executor is in the process of terminating |
|
1404 |
* after {@link #shutdown} or {@link #shutdownNow} but has not |
|
1405 |
* completely terminated. This method may be useful for |
|
1406 |
* debugging. A return of {@code true} reported a sufficient |
|
1407 |
* period after shutdown may indicate that submitted tasks have |
|
1408 |
* ignored or suppressed interruption, causing this executor not |
|
1409 |
* to properly terminate. |
|
1410 |
* |
|
1411 |
* @return true if terminating but not yet terminated |
|
1412 |
*/ |
|
1413 |
public boolean isTerminating() { |
|
1414 |
int c = ctl.get(); |
|
1415 |
return ! isRunning(c) && runStateLessThan(c, TERMINATED); |
|
1416 |
} |
|
1417 |
||
1418 |
public boolean isTerminated() { |
|
1419 |
return runStateAtLeast(ctl.get(), TERMINATED); |
|
1420 |
} |
|
1421 |
||
1422 |
public boolean awaitTermination(long timeout, TimeUnit unit) |
|
1423 |
throws InterruptedException { |
|
1424 |
long nanos = unit.toNanos(timeout); |
|
1425 |
final ReentrantLock mainLock = this.mainLock; |
|
1426 |
mainLock.lock(); |
|
1427 |
try { |
|
1428 |
for (;;) { |
|
1429 |
if (runStateAtLeast(ctl.get(), TERMINATED)) |
|
1430 |
return true; |
|
1431 |
if (nanos <= 0) |
|
1432 |
return false; |
|
1433 |
nanos = termination.awaitNanos(nanos); |
|
1434 |
} |
|
1435 |
} finally { |
|
1436 |
mainLock.unlock(); |
|
1437 |
} |
|
1438 |
} |
|
1439 |
||
1440 |
/** |
|
1441 |
* Invokes {@code shutdown} when this executor is no longer |
|
1442 |
* referenced and it has no threads. |
|
1443 |
*/ |
|
1444 |
protected void finalize() { |
|
1445 |
shutdown(); |
|
1446 |
} |
|
1447 |
||
1448 |
/** |
|
1449 |
* Sets the thread factory used to create new threads. |
|
1450 |
* |
|
1451 |
* @param threadFactory the new thread factory |
|
1452 |
* @throws NullPointerException if threadFactory is null |
|
1453 |
* @see #getThreadFactory |
|
1454 |
*/ |
|
1455 |
public void setThreadFactory(ThreadFactory threadFactory) { |
|
1456 |
if (threadFactory == null) |
|
1457 |
throw new NullPointerException(); |
|
1458 |
this.threadFactory = threadFactory; |
|
1459 |
} |
|
1460 |
||
1461 |
/** |
|
1462 |
* Returns the thread factory used to create new threads. |
|
1463 |
* |
|
1464 |
* @return the current thread factory |
|
1465 |
* @see #setThreadFactory |
|
1466 |
*/ |
|
1467 |
public ThreadFactory getThreadFactory() { |
|
1468 |
return threadFactory; |
|
1469 |
} |
|
1470 |
||
1471 |
/** |
|
1472 |
* Sets a new handler for unexecutable tasks. |
|
1473 |
* |
|
1474 |
* @param handler the new handler |
|
1475 |
* @throws NullPointerException if handler is null |
|
1476 |
* @see #getRejectedExecutionHandler |
|
1477 |
*/ |
|
1478 |
public void setRejectedExecutionHandler(RejectedExecutionHandler handler) { |
|
1479 |
if (handler == null) |
|
1480 |
throw new NullPointerException(); |
|
1481 |
this.handler = handler; |
|
1482 |
} |
|
1483 |
||
1484 |
/** |
|
1485 |
* Returns the current handler for unexecutable tasks. |
|
1486 |
* |
|
1487 |
* @return the current handler |
|
1488 |
* @see #setRejectedExecutionHandler |
|
1489 |
*/ |
|
1490 |
public RejectedExecutionHandler getRejectedExecutionHandler() { |
|
1491 |
return handler; |
|
1492 |
} |
|
1493 |
||
1494 |
/** |
|
1495 |
* Sets the core number of threads. This overrides any value set |
|
1496 |
* in the constructor. If the new value is smaller than the |
|
1497 |
* current value, excess existing threads will be terminated when |
|
1498 |
* they next become idle. If larger, new threads will, if needed, |
|
1499 |
* be started to execute any queued tasks. |
|
1500 |
* |
|
1501 |
* @param corePoolSize the new core size |
|
1502 |
* @throws IllegalArgumentException if {@code corePoolSize < 0} |
|
1503 |
* @see #getCorePoolSize |
|
1504 |
*/ |
|
1505 |
public void setCorePoolSize(int corePoolSize) { |
|
1506 |
if (corePoolSize < 0) |
|
1507 |
throw new IllegalArgumentException(); |
|
1508 |
int delta = corePoolSize - this.corePoolSize; |
|
1509 |
this.corePoolSize = corePoolSize; |
|
1510 |
if (workerCountOf(ctl.get()) > corePoolSize) |
|
1511 |
interruptIdleWorkers(); |
|
1512 |
else if (delta > 0) { |
|
1513 |
// We don't really know how many new threads are "needed". |
|
1514 |
// As a heuristic, prestart enough new workers (up to new |
|
1515 |
// core size) to handle the current number of tasks in |
|
1516 |
// queue, but stop if queue becomes empty while doing so. |
|
1517 |
int k = Math.min(delta, workQueue.size()); |
|
1518 |
while (k-- > 0 && addWorker(null, true)) { |
|
1519 |
if (workQueue.isEmpty()) |
|
1520 |
break; |
|
1521 |
} |
|
1522 |
} |
|
1523 |
} |
|
1524 |
||
1525 |
/** |
|
1526 |
* Returns the core number of threads. |
|
1527 |
* |
|
1528 |
* @return the core number of threads |
|
1529 |
* @see #setCorePoolSize |
|
1530 |
*/ |
|
1531 |
public int getCorePoolSize() { |
|
1532 |
return corePoolSize; |
|
1533 |
} |
|
1534 |
||
1535 |
/** |
|
1536 |
* Starts a core thread, causing it to idly wait for work. This |
|
1537 |
* overrides the default policy of starting core threads only when |
|
1538 |
* new tasks are executed. This method will return {@code false} |
|
1539 |
* if all core threads have already been started. |
|
1540 |
* |
|
1541 |
* @return {@code true} if a thread was started |
|
1542 |
*/ |
|
1543 |
public boolean prestartCoreThread() { |
|
1544 |
return workerCountOf(ctl.get()) < corePoolSize && |
|
1545 |
addWorker(null, true); |
|
1546 |
} |
|
1547 |
||
1548 |
/** |
|
1549 |
* Starts all core threads, causing them to idly wait for work. This |
|
1550 |
* overrides the default policy of starting core threads only when |
|
1551 |
* new tasks are executed. |
|
1552 |
* |
|
1553 |
* @return the number of threads started |
|
1554 |
*/ |
|
1555 |
public int prestartAllCoreThreads() { |
|
1556 |
int n = 0; |
|
1557 |
while (addWorker(null, true)) |
|
1558 |
++n; |
|
1559 |
return n; |
|
1560 |
} |
|
1561 |
||
1562 |
/** |
|
1563 |
* Returns true if this pool allows core threads to time out and |
|
1564 |
* terminate if no tasks arrive within the keepAlive time, being |
|
1565 |
* replaced if needed when new tasks arrive. When true, the same |
|
1566 |
* keep-alive policy applying to non-core threads applies also to |
|
1567 |
* core threads. When false (the default), core threads are never |
|
1568 |
* terminated due to lack of incoming tasks. |
|
1569 |
* |
|
1570 |
* @return {@code true} if core threads are allowed to time out, |
|
1571 |
* else {@code false} |
|
1572 |
* |
|
1573 |
* @since 1.6 |
|
1574 |
*/ |
|
1575 |
public boolean allowsCoreThreadTimeOut() { |
|
1576 |
return allowCoreThreadTimeOut; |
|
1577 |
} |
|
1578 |
||
1579 |
/** |
|
1580 |
* Sets the policy governing whether core threads may time out and |
|
1581 |
* terminate if no tasks arrive within the keep-alive time, being |
|
1582 |
* replaced if needed when new tasks arrive. When false, core |
|
1583 |
* threads are never terminated due to lack of incoming |
|
1584 |
* tasks. When true, the same keep-alive policy applying to |
|
1585 |
* non-core threads applies also to core threads. To avoid |
|
1586 |
* continual thread replacement, the keep-alive time must be |
|
1587 |
* greater than zero when setting {@code true}. This method |
|
1588 |
* should in general be called before the pool is actively used. |
|
1589 |
* |
|
1590 |
* @param value {@code true} if should time out, else {@code false} |
|
1591 |
* @throws IllegalArgumentException if value is {@code true} |
|
1592 |
* and the current keep-alive time is not greater than zero |
|
1593 |
* |
|
1594 |
* @since 1.6 |
|
1595 |
*/ |
|
1596 |
public void allowCoreThreadTimeOut(boolean value) { |
|
1597 |
if (value && keepAliveTime <= 0) |
|
1598 |
throw new IllegalArgumentException("Core threads must have nonzero keep alive times"); |
|
1599 |
if (value != allowCoreThreadTimeOut) { |
|
1600 |
allowCoreThreadTimeOut = value; |
|
1601 |
if (value) |
|
1602 |
interruptIdleWorkers(); |
|
1603 |
} |
|
1604 |
} |
|
1605 |
||
1606 |
/** |
|
1607 |
* Sets the maximum allowed number of threads. This overrides any |
|
1608 |
* value set in the constructor. If the new value is smaller than |
|
1609 |
* the current value, excess existing threads will be |
|
1610 |
* terminated when they next become idle. |
|
1611 |
* |
|
1612 |
* @param maximumPoolSize the new maximum |
|
1613 |
* @throws IllegalArgumentException if the new maximum is |
|
1614 |
* less than or equal to zero, or |
|
1615 |
* less than the {@linkplain #getCorePoolSize core pool size} |
|
1616 |
* @see #getMaximumPoolSize |
|
1617 |
*/ |
|
1618 |
public void setMaximumPoolSize(int maximumPoolSize) { |
|
1619 |
if (maximumPoolSize <= 0 || maximumPoolSize < corePoolSize) |
|
1620 |
throw new IllegalArgumentException(); |
|
1621 |
this.maximumPoolSize = maximumPoolSize; |
|
1622 |
if (workerCountOf(ctl.get()) > maximumPoolSize) |
|
1623 |
interruptIdleWorkers(); |
|
1624 |
} |
|
1625 |
||
1626 |
/** |
|
1627 |
* Returns the maximum allowed number of threads. |
|
1628 |
* |
|
1629 |
* @return the maximum allowed number of threads |
|
1630 |
* @see #setMaximumPoolSize |
|
1631 |
*/ |
|
1632 |
public int getMaximumPoolSize() { |
|
1633 |
return maximumPoolSize; |
|
1634 |
} |
|
1635 |
||
1636 |
/** |
|
1637 |
* Sets the time limit for which threads may remain idle before |
|
1638 |
* being terminated. If there are more than the core number of |
|
1639 |
* threads currently in the pool, after waiting this amount of |
|
1640 |
* time without processing a task, excess threads will be |
|
1641 |
* terminated. This overrides any value set in the constructor. |
|
1642 |
* |
|
1643 |
* @param time the time to wait. A time value of zero will cause |
|
1644 |
* excess threads to terminate immediately after executing tasks. |
|
1645 |
* @param unit the time unit of the {@code time} argument |
|
1646 |
* @throws IllegalArgumentException if {@code time} less than zero or |
|
1647 |
* if {@code time} is zero and {@code allowsCoreThreadTimeOut} |
|
1648 |
* @see #getKeepAliveTime |
|
1649 |
*/ |
|
1650 |
public void setKeepAliveTime(long time, TimeUnit unit) { |
|
1651 |
if (time < 0) |
|
1652 |
throw new IllegalArgumentException(); |
|
1653 |
if (time == 0 && allowsCoreThreadTimeOut()) |
|
1654 |
throw new IllegalArgumentException("Core threads must have nonzero keep alive times"); |
|
1655 |
long keepAliveTime = unit.toNanos(time); |
|
1656 |
long delta = keepAliveTime - this.keepAliveTime; |
|
1657 |
this.keepAliveTime = keepAliveTime; |
|
1658 |
if (delta < 0) |
|
1659 |
interruptIdleWorkers(); |
|
1660 |
} |
|
1661 |
||
1662 |
/** |
|
1663 |
* Returns the thread keep-alive time, which is the amount of time |
|
1664 |
* that threads in excess of the core pool size may remain |
|
1665 |
* idle before being terminated. |
|
1666 |
* |
|
1667 |
* @param unit the desired time unit of the result |
|
1668 |
* @return the time limit |
|
1669 |
* @see #setKeepAliveTime |
|
1670 |
*/ |
|
1671 |
public long getKeepAliveTime(TimeUnit unit) { |
|
1672 |
return unit.convert(keepAliveTime, TimeUnit.NANOSECONDS); |
|
1673 |
} |
|
1674 |
||
1675 |
/* User-level queue utilities */ |
|
1676 |
||
1677 |
/** |
|
1678 |
* Returns the task queue used by this executor. Access to the |
|
1679 |
* task queue is intended primarily for debugging and monitoring. |
|
1680 |
* This queue may be in active use. Retrieving the task queue |
|
1681 |
* does not prevent queued tasks from executing. |
|
1682 |
* |
|
1683 |
* @return the task queue |
|
1684 |
*/ |
|
1685 |
public BlockingQueue<Runnable> getQueue() { |
|
1686 |
return workQueue; |
|
1687 |
} |
|
1688 |
||
1689 |
/** |
|
1690 |
* Removes this task from the executor's internal queue if it is |
|
1691 |
* present, thus causing it not to be run if it has not already |
|
1692 |
* started. |
|
1693 |
* |
|
1694 |
* <p> This method may be useful as one part of a cancellation |
|
1695 |
* scheme. It may fail to remove tasks that have been converted |
|
1696 |
* into other forms before being placed on the internal queue. For |
|
1697 |
* example, a task entered using {@code submit} might be |
|
1698 |
* converted into a form that maintains {@code Future} status. |
|
1699 |
* However, in such cases, method {@link #purge} may be used to |
|
1700 |
* remove those Futures that have been cancelled. |
|
1701 |
* |
|
1702 |
* @param task the task to remove |
|
1703 |
* @return true if the task was removed |
|
1704 |
*/ |
|
1705 |
public boolean remove(Runnable task) { |
|
1706 |
boolean removed = workQueue.remove(task); |
|
1707 |
tryTerminate(); // In case SHUTDOWN and now empty |
|
1708 |
return removed; |
|
1709 |
} |
|
1710 |
||
1711 |
/** |
|
1712 |
* Tries to remove from the work queue all {@link Future} |
|
1713 |
* tasks that have been cancelled. This method can be useful as a |
|
1714 |
* storage reclamation operation, that has no other impact on |
|
1715 |
* functionality. Cancelled tasks are never executed, but may |
|
1716 |
* accumulate in work queues until worker threads can actively |
|
1717 |
* remove them. Invoking this method instead tries to remove them now. |
|
1718 |
* However, this method may fail to remove tasks in |
|
1719 |
* the presence of interference by other threads. |
|
1720 |
*/ |
|
1721 |
public void purge() { |
|
1722 |
final BlockingQueue<Runnable> q = workQueue; |
|
1723 |
try { |
|
1724 |
Iterator<Runnable> it = q.iterator(); |
|
1725 |
while (it.hasNext()) { |
|
1726 |
Runnable r = it.next(); |
|
1727 |
if (r instanceof Future<?> && ((Future<?>)r).isCancelled()) |
|
1728 |
it.remove(); |
|
1729 |
} |
|
1730 |
} catch (ConcurrentModificationException fallThrough) { |
|
1731 |
// Take slow path if we encounter interference during traversal. |
|
1732 |
// Make copy for traversal and call remove for cancelled entries. |
|
1733 |
// The slow path is more likely to be O(N*N). |
|
1734 |
for (Object r : q.toArray()) |
|
1735 |
if (r instanceof Future<?> && ((Future<?>)r).isCancelled()) |
|
1736 |
q.remove(r); |
|
1737 |
} |
|
1738 |
||
1739 |
tryTerminate(); // In case SHUTDOWN and now empty |
|
1740 |
} |
|
1741 |
||
1742 |
/* Statistics */ |
|
1743 |
||
1744 |
/** |
|
1745 |
* Returns the current number of threads in the pool. |
|
1746 |
* |
|
1747 |
* @return the number of threads |
|
1748 |
*/ |
|
1749 |
public int getPoolSize() { |
|
1750 |
final ReentrantLock mainLock = this.mainLock; |
|
1751 |
mainLock.lock(); |
|
1752 |
try { |
|
1753 |
// Remove rare and surprising possibility of |
|
1754 |
// isTerminated() && getPoolSize() > 0 |
|
1755 |
return runStateAtLeast(ctl.get(), TIDYING) ? 0 |
|
1756 |
: workers.size(); |
|
1757 |
} finally { |
|
1758 |
mainLock.unlock(); |
|
1759 |
} |
|
1760 |
} |
|
1761 |
||
1762 |
/** |
|
1763 |
* Returns the approximate number of threads that are actively |
|
1764 |
* executing tasks. |
|
1765 |
* |
|
1766 |
* @return the number of threads |
|
1767 |
*/ |
|
1768 |
public int getActiveCount() { |
|
1769 |
final ReentrantLock mainLock = this.mainLock; |
|
1770 |
mainLock.lock(); |
|
1771 |
try { |
|
1772 |
int n = 0; |
|
1773 |
for (Worker w : workers) |
|
1774 |
if (w.isLocked()) |
|
1775 |
++n; |
|
1776 |
return n; |
|
1777 |
} finally { |
|
1778 |
mainLock.unlock(); |
|
1779 |
} |
|
1780 |
} |
|
1781 |
||
1782 |
/** |
|
1783 |
* Returns the largest number of threads that have ever |
|
1784 |
* simultaneously been in the pool. |
|
1785 |
* |
|
1786 |
* @return the number of threads |
|
1787 |
*/ |
|
1788 |
public int getLargestPoolSize() { |
|
1789 |
final ReentrantLock mainLock = this.mainLock; |
|
1790 |
mainLock.lock(); |
|
1791 |
try { |
|
1792 |
return largestPoolSize; |
|
1793 |
} finally { |
|
1794 |
mainLock.unlock(); |
|
1795 |
} |
|
1796 |
} |
|
1797 |
||
1798 |
/** |
|
1799 |
* Returns the approximate total number of tasks that have ever been |
|
1800 |
* scheduled for execution. Because the states of tasks and |
|
1801 |
* threads may change dynamically during computation, the returned |
|
1802 |
* value is only an approximation. |
|
1803 |
* |
|
1804 |
* @return the number of tasks |
|
1805 |
*/ |
|
1806 |
public long getTaskCount() { |
|
1807 |
final ReentrantLock mainLock = this.mainLock; |
|
1808 |
mainLock.lock(); |
|
1809 |
try { |
|
1810 |
long n = completedTaskCount; |
|
1811 |
for (Worker w : workers) { |
|
1812 |
n += w.completedTasks; |
|
1813 |
if (w.isLocked()) |
|
1814 |
++n; |
|
1815 |
} |
|
1816 |
return n + workQueue.size(); |
|
1817 |
} finally { |
|
1818 |
mainLock.unlock(); |
|
1819 |
} |
|
1820 |
} |
|
1821 |
||
1822 |
/** |
|
1823 |
* Returns the approximate total number of tasks that have |
|
1824 |
* completed execution. Because the states of tasks and threads |
|
1825 |
* may change dynamically during computation, the returned value |
|
1826 |
* is only an approximation, but one that does not ever decrease |
|
1827 |
* across successive calls. |
|
1828 |
* |
|
1829 |
* @return the number of tasks |
|
1830 |
*/ |
|
1831 |
public long getCompletedTaskCount() { |
|
1832 |
final ReentrantLock mainLock = this.mainLock; |
|
1833 |
mainLock.lock(); |
|
1834 |
try { |
|
1835 |
long n = completedTaskCount; |
|
1836 |
for (Worker w : workers) |
|
1837 |
n += w.completedTasks; |
|
1838 |
return n; |
|
1839 |
} finally { |
|
1840 |
mainLock.unlock(); |
|
1841 |
} |
|
1842 |
} |
|
1843 |
||
7976
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|
1844 |
/** |
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changeset
|
1845 |
* Returns a string identifying this pool, as well as its state, |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
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changeset
|
1846 |
* including indications of run state and estimated worker and |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
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parents:
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diff
changeset
|
1847 |
* task counts. |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
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parents:
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diff
changeset
|
1848 |
* |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
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diff
changeset
|
1849 |
* @return a string identifying this pool, as well as its state |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
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parents:
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diff
changeset
|
1850 |
*/ |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
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parents:
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diff
changeset
|
1851 |
public String toString() { |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
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parents:
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diff
changeset
|
1852 |
long ncompleted; |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1853 |
int nworkers, nactive; |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
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diff
changeset
|
1854 |
final ReentrantLock mainLock = this.mainLock; |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
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diff
changeset
|
1855 |
mainLock.lock(); |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
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diff
changeset
|
1856 |
try { |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
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diff
changeset
|
1857 |
ncompleted = completedTaskCount; |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
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diff
changeset
|
1858 |
nactive = 0; |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
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diff
changeset
|
1859 |
nworkers = workers.size(); |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1860 |
for (Worker w : workers) { |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1861 |
ncompleted += w.completedTasks; |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
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diff
changeset
|
1862 |
if (w.isLocked()) |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1863 |
++nactive; |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1864 |
} |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1865 |
} finally { |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1866 |
mainLock.unlock(); |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1867 |
} |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1868 |
int c = ctl.get(); |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1869 |
String rs = (runStateLessThan(c, SHUTDOWN) ? "Running" : |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1870 |
(runStateAtLeast(c, TERMINATED) ? "Terminated" : |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1871 |
"Shutting down")); |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1872 |
return super.toString() + |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1873 |
"[" + rs + |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1874 |
", pool size = " + nworkers + |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1875 |
", active threads = " + nactive + |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1876 |
", queued tasks = " + workQueue.size() + |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1877 |
", completed tasks = " + ncompleted + |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1878 |
"]"; |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1879 |
} |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
1880 |
|
2 | 1881 |
/* Extension hooks */ |
1882 |
||
1883 |
/** |
|
1884 |
* Method invoked prior to executing the given Runnable in the |
|
1885 |
* given thread. This method is invoked by thread {@code t} that |
|
1886 |
* will execute task {@code r}, and may be used to re-initialize |
|
1887 |
* ThreadLocals, or to perform logging. |
|
1888 |
* |
|
1889 |
* <p>This implementation does nothing, but may be customized in |
|
1890 |
* subclasses. Note: To properly nest multiple overridings, subclasses |
|
1891 |
* should generally invoke {@code super.beforeExecute} at the end of |
|
1892 |
* this method. |
|
1893 |
* |
|
1894 |
* @param t the thread that will run task {@code r} |
|
1895 |
* @param r the task that will be executed |
|
1896 |
*/ |
|
1897 |
protected void beforeExecute(Thread t, Runnable r) { } |
|
1898 |
||
1899 |
/** |
|
1900 |
* Method invoked upon completion of execution of the given Runnable. |
|
1901 |
* This method is invoked by the thread that executed the task. If |
|
1902 |
* non-null, the Throwable is the uncaught {@code RuntimeException} |
|
1903 |
* or {@code Error} that caused execution to terminate abruptly. |
|
1904 |
* |
|
1905 |
* <p>This implementation does nothing, but may be customized in |
|
1906 |
* subclasses. Note: To properly nest multiple overridings, subclasses |
|
1907 |
* should generally invoke {@code super.afterExecute} at the |
|
1908 |
* beginning of this method. |
|
1909 |
* |
|
1910 |
* <p><b>Note:</b> When actions are enclosed in tasks (such as |
|
1911 |
* {@link FutureTask}) either explicitly or via methods such as |
|
1912 |
* {@code submit}, these task objects catch and maintain |
|
1913 |
* computational exceptions, and so they do not cause abrupt |
|
1914 |
* termination, and the internal exceptions are <em>not</em> |
|
1915 |
* passed to this method. If you would like to trap both kinds of |
|
1916 |
* failures in this method, you can further probe for such cases, |
|
1917 |
* as in this sample subclass that prints either the direct cause |
|
1918 |
* or the underlying exception if a task has been aborted: |
|
1919 |
* |
|
1920 |
* <pre> {@code |
|
1921 |
* class ExtendedExecutor extends ThreadPoolExecutor { |
|
1922 |
* // ... |
|
1923 |
* protected void afterExecute(Runnable r, Throwable t) { |
|
1924 |
* super.afterExecute(r, t); |
|
1925 |
* if (t == null && r instanceof Future<?>) { |
|
1926 |
* try { |
|
1927 |
* Object result = ((Future<?>) r).get(); |
|
1928 |
* } catch (CancellationException ce) { |
|
1929 |
* t = ce; |
|
1930 |
* } catch (ExecutionException ee) { |
|
1931 |
* t = ee.getCause(); |
|
1932 |
* } catch (InterruptedException ie) { |
|
1933 |
* Thread.currentThread().interrupt(); // ignore/reset |
|
1934 |
* } |
|
1935 |
* } |
|
1936 |
* if (t != null) |
|
1937 |
* System.out.println(t); |
|
1938 |
* } |
|
1939 |
* }}</pre> |
|
1940 |
* |
|
1941 |
* @param r the runnable that has completed |
|
1942 |
* @param t the exception that caused termination, or null if |
|
1943 |
* execution completed normally |
|
1944 |
*/ |
|
1945 |
protected void afterExecute(Runnable r, Throwable t) { } |
|
1946 |
||
1947 |
/** |
|
1948 |
* Method invoked when the Executor has terminated. Default |
|
1949 |
* implementation does nothing. Note: To properly nest multiple |
|
1950 |
* overridings, subclasses should generally invoke |
|
1951 |
* {@code super.terminated} within this method. |
|
1952 |
*/ |
|
1953 |
protected void terminated() { } |
|
1954 |
||
1955 |
/* Predefined RejectedExecutionHandlers */ |
|
1956 |
||
1957 |
/** |
|
1958 |
* A handler for rejected tasks that runs the rejected task |
|
1959 |
* directly in the calling thread of the {@code execute} method, |
|
1960 |
* unless the executor has been shut down, in which case the task |
|
1961 |
* is discarded. |
|
1962 |
*/ |
|
1963 |
public static class CallerRunsPolicy implements RejectedExecutionHandler { |
|
1964 |
/** |
|
1965 |
* Creates a {@code CallerRunsPolicy}. |
|
1966 |
*/ |
|
1967 |
public CallerRunsPolicy() { } |
|
1968 |
||
1969 |
/** |
|
1970 |
* Executes task r in the caller's thread, unless the executor |
|
1971 |
* has been shut down, in which case the task is discarded. |
|
1972 |
* |
|
1973 |
* @param r the runnable task requested to be executed |
|
1974 |
* @param e the executor attempting to execute this task |
|
1975 |
*/ |
|
1976 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
|
1977 |
if (!e.isShutdown()) { |
|
1978 |
r.run(); |
|
1979 |
} |
|
1980 |
} |
|
1981 |
} |
|
1982 |
||
1983 |
/** |
|
1984 |
* A handler for rejected tasks that throws a |
|
1985 |
* {@code RejectedExecutionException}. |
|
1986 |
*/ |
|
1987 |
public static class AbortPolicy implements RejectedExecutionHandler { |
|
1988 |
/** |
|
1989 |
* Creates an {@code AbortPolicy}. |
|
1990 |
*/ |
|
1991 |
public AbortPolicy() { } |
|
1992 |
||
1993 |
/** |
|
1994 |
* Always throws RejectedExecutionException. |
|
1995 |
* |
|
1996 |
* @param r the runnable task requested to be executed |
|
1997 |
* @param e the executor attempting to execute this task |
|
1998 |
* @throws RejectedExecutionException always. |
|
1999 |
*/ |
|
2000 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
|
7976
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
2001 |
throw new RejectedExecutionException("Task " + r.toString() + |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
2002 |
" rejected from " + |
f273c0d04215
7005424: Resync java.util.concurrent classes with Dougs CVS - Jan 2011
dl
parents:
5506
diff
changeset
|
2003 |
e.toString()); |
2 | 2004 |
} |
2005 |
} |
|
2006 |
||
2007 |
/** |
|
2008 |
* A handler for rejected tasks that silently discards the |
|
2009 |
* rejected task. |
|
2010 |
*/ |
|
2011 |
public static class DiscardPolicy implements RejectedExecutionHandler { |
|
2012 |
/** |
|
2013 |
* Creates a {@code DiscardPolicy}. |
|
2014 |
*/ |
|
2015 |
public DiscardPolicy() { } |
|
2016 |
||
2017 |
/** |
|
2018 |
* Does nothing, which has the effect of discarding task r. |
|
2019 |
* |
|
2020 |
* @param r the runnable task requested to be executed |
|
2021 |
* @param e the executor attempting to execute this task |
|
2022 |
*/ |
|
2023 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
|
2024 |
} |
|
2025 |
} |
|
2026 |
||
2027 |
/** |
|
2028 |
* A handler for rejected tasks that discards the oldest unhandled |
|
2029 |
* request and then retries {@code execute}, unless the executor |
|
2030 |
* is shut down, in which case the task is discarded. |
|
2031 |
*/ |
|
2032 |
public static class DiscardOldestPolicy implements RejectedExecutionHandler { |
|
2033 |
/** |
|
2034 |
* Creates a {@code DiscardOldestPolicy} for the given executor. |
|
2035 |
*/ |
|
2036 |
public DiscardOldestPolicy() { } |
|
2037 |
||
2038 |
/** |
|
2039 |
* Obtains and ignores the next task that the executor |
|
2040 |
* would otherwise execute, if one is immediately available, |
|
2041 |
* and then retries execution of task r, unless the executor |
|
2042 |
* is shut down, in which case task r is instead discarded. |
|
2043 |
* |
|
2044 |
* @param r the runnable task requested to be executed |
|
2045 |
* @param e the executor attempting to execute this task |
|
2046 |
*/ |
|
2047 |
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) { |
|
2048 |
if (!e.isShutdown()) { |
|
2049 |
e.getQueue().poll(); |
|
2050 |
e.execute(r); |
|
2051 |
} |
|
2052 |
} |
|
2053 |
} |
|
2054 |
} |