author | mr |
Tue, 29 Oct 2019 08:26:55 -0700 | |
changeset 58842 | 6c255334120d |
parent 50719 | 106dc156ce6b |
permissions | -rw-r--r-- |
2 | 1 |
/* |
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* Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved. |
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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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package java.lang; |
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import jdk.internal.misc.TerminatingThreadLocal; |
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import java.lang.ref.*; |
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import java.util.Objects; |
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import java.util.concurrent.atomic.AtomicInteger; |
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import java.util.function.Supplier; |
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/** |
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* This class provides thread-local variables. These variables differ from |
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* their normal counterparts in that each thread that accesses one (via its |
|
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* {@code get} or {@code set} method) has its own, independently initialized |
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* copy of the variable. {@code ThreadLocal} instances are typically private |
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* static fields in classes that wish to associate state with a thread (e.g., |
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* a user ID or Transaction ID). |
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* |
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* <p>For example, the class below generates unique identifiers local to each |
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* thread. |
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* A thread's id is assigned the first time it invokes {@code ThreadId.get()} |
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* and remains unchanged on subsequent calls. |
46 |
* <pre> |
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* import java.util.concurrent.atomic.AtomicInteger; |
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* |
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* public class ThreadId { |
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* // Atomic integer containing the next thread ID to be assigned |
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* private static final AtomicInteger nextId = new AtomicInteger(0); |
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* |
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* // Thread local variable containing each thread's ID |
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* private static final ThreadLocal<Integer> threadId = |
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* new ThreadLocal<Integer>() { |
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* @Override protected Integer initialValue() { |
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* return nextId.getAndIncrement(); |
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* } |
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* }; |
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* |
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* // Returns the current thread's unique ID, assigning it if necessary |
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* public static int get() { |
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* return threadId.get(); |
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* } |
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* } |
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* </pre> |
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* <p>Each thread holds an implicit reference to its copy of a thread-local |
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* variable as long as the thread is alive and the {@code ThreadLocal} |
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* instance is accessible; after a thread goes away, all of its copies of |
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* thread-local instances are subject to garbage collection (unless other |
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* references to these copies exist). |
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* |
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* @author Josh Bloch and Doug Lea |
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* @since 1.2 |
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*/ |
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public class ThreadLocal<T> { |
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/** |
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* ThreadLocals rely on per-thread linear-probe hash maps attached |
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* to each thread (Thread.threadLocals and |
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* inheritableThreadLocals). The ThreadLocal objects act as keys, |
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* searched via threadLocalHashCode. This is a custom hash code |
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* (useful only within ThreadLocalMaps) that eliminates collisions |
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* in the common case where consecutively constructed ThreadLocals |
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* are used by the same threads, while remaining well-behaved in |
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* less common cases. |
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*/ |
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private final int threadLocalHashCode = nextHashCode(); |
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/** |
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* The next hash code to be given out. Updated atomically. Starts at |
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* zero. |
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*/ |
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private static AtomicInteger nextHashCode = |
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new AtomicInteger(); |
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/** |
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* The difference between successively generated hash codes - turns |
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* implicit sequential thread-local IDs into near-optimally spread |
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* multiplicative hash values for power-of-two-sized tables. |
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*/ |
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private static final int HASH_INCREMENT = 0x61c88647; |
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/** |
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* Returns the next hash code. |
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*/ |
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private static int nextHashCode() { |
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return nextHashCode.getAndAdd(HASH_INCREMENT); |
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} |
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/** |
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* Returns the current thread's "initial value" for this |
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* thread-local variable. This method will be invoked the first |
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* time a thread accesses the variable with the {@link #get} |
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* method, unless the thread previously invoked the {@link #set} |
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* method, in which case the {@code initialValue} method will not |
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* be invoked for the thread. Normally, this method is invoked at |
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* most once per thread, but it may be invoked again in case of |
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* subsequent invocations of {@link #remove} followed by {@link #get}. |
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* |
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* <p>This implementation simply returns {@code null}; if the |
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* programmer desires thread-local variables to have an initial |
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* value other than {@code null}, {@code ThreadLocal} must be |
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* subclassed, and this method overridden. Typically, an |
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* anonymous inner class will be used. |
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* |
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* @return the initial value for this thread-local |
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*/ |
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protected T initialValue() { |
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return null; |
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} |
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/** |
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* Creates a thread local variable. The initial value of the variable is |
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* determined by invoking the {@code get} method on the {@code Supplier}. |
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* |
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* @param <S> the type of the thread local's value |
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* @param supplier the supplier to be used to determine the initial value |
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* @return a new thread local variable |
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* @throws NullPointerException if the specified supplier is null |
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* @since 1.8 |
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*/ |
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public static <S> ThreadLocal<S> withInitial(Supplier<? extends S> supplier) { |
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return new SuppliedThreadLocal<>(supplier); |
144 |
} |
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/** |
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* Creates a thread local variable. |
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* @see #withInitial(java.util.function.Supplier) |
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*/ |
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public ThreadLocal() { |
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} |
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/** |
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* Returns the value in the current thread's copy of this |
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* thread-local variable. If the variable has no value for the |
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* current thread, it is first initialized to the value returned |
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* by an invocation of the {@link #initialValue} method. |
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* |
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* @return the current thread's value of this thread-local |
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*/ |
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public T get() { |
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Thread t = Thread.currentThread(); |
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ThreadLocalMap map = getMap(t); |
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if (map != null) { |
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ThreadLocalMap.Entry e = map.getEntry(this); |
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if (e != null) { |
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@SuppressWarnings("unchecked") |
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T result = (T)e.value; |
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return result; |
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} |
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} |
172 |
return setInitialValue(); |
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} |
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/** |
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* Returns {@code true} if there is a value in the current thread's copy of |
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* this thread-local variable, even if that values is {@code null}. |
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* |
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* @return {@code true} if current thread has associated value in this |
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* thread-local variable; {@code false} if not |
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*/ |
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boolean isPresent() { |
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Thread t = Thread.currentThread(); |
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ThreadLocalMap map = getMap(t); |
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return map != null && map.getEntry(this) != null; |
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} |
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|
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/** |
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* Variant of set() to establish initialValue. Used instead |
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* of set() in case user has overridden the set() method. |
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* |
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* @return the initial value |
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*/ |
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private T setInitialValue() { |
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T value = initialValue(); |
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Thread t = Thread.currentThread(); |
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ThreadLocalMap map = getMap(t); |
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if (map != null) { |
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map.set(this, value); |
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} else { |
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createMap(t, value); |
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} |
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if (this instanceof TerminatingThreadLocal) { |
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TerminatingThreadLocal.register((TerminatingThreadLocal<?>) this); |
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} |
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return value; |
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} |
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||
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/** |
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* Sets the current thread's copy of this thread-local variable |
|
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* to the specified value. Most subclasses will have no need to |
|
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* override this method, relying solely on the {@link #initialValue} |
|
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* method to set the values of thread-locals. |
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* |
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* @param value the value to be stored in the current thread's copy of |
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* this thread-local. |
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*/ |
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public void set(T value) { |
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Thread t = Thread.currentThread(); |
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ThreadLocalMap map = getMap(t); |
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if (map != null) { |
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map.set(this, value); |
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} else { |
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createMap(t, value); |
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} |
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} |
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||
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/** |
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* Removes the current thread's value for this thread-local |
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* variable. If this thread-local variable is subsequently |
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* {@linkplain #get read} by the current thread, its value will be |
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* reinitialized by invoking its {@link #initialValue} method, |
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* unless its value is {@linkplain #set set} by the current thread |
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* in the interim. This may result in multiple invocations of the |
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* {@code initialValue} method in the current thread. |
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* |
237 |
* @since 1.5 |
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*/ |
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public void remove() { |
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ThreadLocalMap m = getMap(Thread.currentThread()); |
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if (m != null) { |
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m.remove(this); |
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} |
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} |
245 |
||
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/** |
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* Get the map associated with a ThreadLocal. Overridden in |
|
248 |
* InheritableThreadLocal. |
|
249 |
* |
|
250 |
* @param t the current thread |
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* @return the map |
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252 |
*/ |
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253 |
ThreadLocalMap getMap(Thread t) { |
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return t.threadLocals; |
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} |
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||
257 |
/** |
|
258 |
* Create the map associated with a ThreadLocal. Overridden in |
|
259 |
* InheritableThreadLocal. |
|
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* |
|
261 |
* @param t the current thread |
|
262 |
* @param firstValue value for the initial entry of the map |
|
263 |
*/ |
|
264 |
void createMap(Thread t, T firstValue) { |
|
265 |
t.threadLocals = new ThreadLocalMap(this, firstValue); |
|
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} |
|
267 |
||
268 |
/** |
|
269 |
* Factory method to create map of inherited thread locals. |
|
270 |
* Designed to be called only from Thread constructor. |
|
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* |
|
272 |
* @param parentMap the map associated with parent thread |
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273 |
* @return a map containing the parent's inheritable bindings |
|
274 |
*/ |
|
275 |
static ThreadLocalMap createInheritedMap(ThreadLocalMap parentMap) { |
|
276 |
return new ThreadLocalMap(parentMap); |
|
277 |
} |
|
278 |
||
279 |
/** |
|
280 |
* Method childValue is visibly defined in subclass |
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281 |
* InheritableThreadLocal, but is internally defined here for the |
|
282 |
* sake of providing createInheritedMap factory method without |
|
283 |
* needing to subclass the map class in InheritableThreadLocal. |
|
284 |
* This technique is preferable to the alternative of embedding |
|
285 |
* instanceof tests in methods. |
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286 |
*/ |
|
287 |
T childValue(T parentValue) { |
|
288 |
throw new UnsupportedOperationException(); |
|
289 |
} |
|
290 |
||
291 |
/** |
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* An extension of ThreadLocal that obtains its initial value from |
293 |
* the specified {@code Supplier}. |
|
294 |
*/ |
|
295 |
static final class SuppliedThreadLocal<T> extends ThreadLocal<T> { |
|
296 |
||
297 |
private final Supplier<? extends T> supplier; |
|
298 |
||
299 |
SuppliedThreadLocal(Supplier<? extends T> supplier) { |
|
300 |
this.supplier = Objects.requireNonNull(supplier); |
|
301 |
} |
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302 |
||
303 |
@Override |
|
304 |
protected T initialValue() { |
|
305 |
return supplier.get(); |
|
306 |
} |
|
307 |
} |
|
308 |
||
309 |
/** |
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2 | 310 |
* ThreadLocalMap is a customized hash map suitable only for |
311 |
* maintaining thread local values. No operations are exported |
|
312 |
* outside of the ThreadLocal class. The class is package private to |
|
313 |
* allow declaration of fields in class Thread. To help deal with |
|
314 |
* very large and long-lived usages, the hash table entries use |
|
315 |
* WeakReferences for keys. However, since reference queues are not |
|
316 |
* used, stale entries are guaranteed to be removed only when |
|
317 |
* the table starts running out of space. |
|
318 |
*/ |
|
319 |
static class ThreadLocalMap { |
|
320 |
||
321 |
/** |
|
322 |
* The entries in this hash map extend WeakReference, using |
|
323 |
* its main ref field as the key (which is always a |
|
324 |
* ThreadLocal object). Note that null keys (i.e. entry.get() |
|
325 |
* == null) mean that the key is no longer referenced, so the |
|
326 |
* entry can be expunged from table. Such entries are referred to |
|
327 |
* as "stale entries" in the code that follows. |
|
328 |
*/ |
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11275 | 329 |
static class Entry extends WeakReference<ThreadLocal<?>> { |
2 | 330 |
/** The value associated with this ThreadLocal. */ |
331 |
Object value; |
|
332 |
||
11275 | 333 |
Entry(ThreadLocal<?> k, Object v) { |
2 | 334 |
super(k); |
335 |
value = v; |
|
336 |
} |
|
337 |
} |
|
338 |
||
339 |
/** |
|
340 |
* The initial capacity -- MUST be a power of two. |
|
341 |
*/ |
|
342 |
private static final int INITIAL_CAPACITY = 16; |
|
343 |
||
344 |
/** |
|
345 |
* The table, resized as necessary. |
|
346 |
* table.length MUST always be a power of two. |
|
347 |
*/ |
|
348 |
private Entry[] table; |
|
349 |
||
350 |
/** |
|
351 |
* The number of entries in the table. |
|
352 |
*/ |
|
353 |
private int size = 0; |
|
354 |
||
355 |
/** |
|
356 |
* The next size value at which to resize. |
|
357 |
*/ |
|
358 |
private int threshold; // Default to 0 |
|
359 |
||
360 |
/** |
|
361 |
* Set the resize threshold to maintain at worst a 2/3 load factor. |
|
362 |
*/ |
|
363 |
private void setThreshold(int len) { |
|
364 |
threshold = len * 2 / 3; |
|
365 |
} |
|
366 |
||
367 |
/** |
|
368 |
* Increment i modulo len. |
|
369 |
*/ |
|
370 |
private static int nextIndex(int i, int len) { |
|
371 |
return ((i + 1 < len) ? i + 1 : 0); |
|
372 |
} |
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373 |
||
374 |
/** |
|
375 |
* Decrement i modulo len. |
|
376 |
*/ |
|
377 |
private static int prevIndex(int i, int len) { |
|
378 |
return ((i - 1 >= 0) ? i - 1 : len - 1); |
|
379 |
} |
|
380 |
||
381 |
/** |
|
382 |
* Construct a new map initially containing (firstKey, firstValue). |
|
383 |
* ThreadLocalMaps are constructed lazily, so we only create |
|
384 |
* one when we have at least one entry to put in it. |
|
385 |
*/ |
|
11275 | 386 |
ThreadLocalMap(ThreadLocal<?> firstKey, Object firstValue) { |
2 | 387 |
table = new Entry[INITIAL_CAPACITY]; |
388 |
int i = firstKey.threadLocalHashCode & (INITIAL_CAPACITY - 1); |
|
389 |
table[i] = new Entry(firstKey, firstValue); |
|
390 |
size = 1; |
|
391 |
setThreshold(INITIAL_CAPACITY); |
|
392 |
} |
|
393 |
||
394 |
/** |
|
395 |
* Construct a new map including all Inheritable ThreadLocals |
|
396 |
* from given parent map. Called only by createInheritedMap. |
|
397 |
* |
|
398 |
* @param parentMap the map associated with parent thread. |
|
399 |
*/ |
|
400 |
private ThreadLocalMap(ThreadLocalMap parentMap) { |
|
401 |
Entry[] parentTable = parentMap.table; |
|
402 |
int len = parentTable.length; |
|
403 |
setThreshold(len); |
|
404 |
table = new Entry[len]; |
|
405 |
||
22581
e868cde95050
8032779: Update code in java.lang to use newer language features
psandoz
parents:
18776
diff
changeset
|
406 |
for (Entry e : parentTable) { |
2 | 407 |
if (e != null) { |
11275 | 408 |
@SuppressWarnings("unchecked") |
409 |
ThreadLocal<Object> key = (ThreadLocal<Object>) e.get(); |
|
2 | 410 |
if (key != null) { |
411 |
Object value = key.childValue(e.value); |
|
412 |
Entry c = new Entry(key, value); |
|
413 |
int h = key.threadLocalHashCode & (len - 1); |
|
414 |
while (table[h] != null) |
|
415 |
h = nextIndex(h, len); |
|
416 |
table[h] = c; |
|
417 |
size++; |
|
418 |
} |
|
419 |
} |
|
420 |
} |
|
421 |
} |
|
422 |
||
423 |
/** |
|
424 |
* Get the entry associated with key. This method |
|
425 |
* itself handles only the fast path: a direct hit of existing |
|
426 |
* key. It otherwise relays to getEntryAfterMiss. This is |
|
427 |
* designed to maximize performance for direct hits, in part |
|
428 |
* by making this method readily inlinable. |
|
429 |
* |
|
430 |
* @param key the thread local object |
|
431 |
* @return the entry associated with key, or null if no such |
|
432 |
*/ |
|
11275 | 433 |
private Entry getEntry(ThreadLocal<?> key) { |
2 | 434 |
int i = key.threadLocalHashCode & (table.length - 1); |
435 |
Entry e = table[i]; |
|
436 |
if (e != null && e.get() == key) |
|
437 |
return e; |
|
438 |
else |
|
439 |
return getEntryAfterMiss(key, i, e); |
|
440 |
} |
|
441 |
||
442 |
/** |
|
443 |
* Version of getEntry method for use when key is not found in |
|
444 |
* its direct hash slot. |
|
445 |
* |
|
446 |
* @param key the thread local object |
|
447 |
* @param i the table index for key's hash code |
|
448 |
* @param e the entry at table[i] |
|
449 |
* @return the entry associated with key, or null if no such |
|
450 |
*/ |
|
11275 | 451 |
private Entry getEntryAfterMiss(ThreadLocal<?> key, int i, Entry e) { |
2 | 452 |
Entry[] tab = table; |
453 |
int len = tab.length; |
|
454 |
||
455 |
while (e != null) { |
|
11275 | 456 |
ThreadLocal<?> k = e.get(); |
2 | 457 |
if (k == key) |
458 |
return e; |
|
459 |
if (k == null) |
|
460 |
expungeStaleEntry(i); |
|
461 |
else |
|
462 |
i = nextIndex(i, len); |
|
463 |
e = tab[i]; |
|
464 |
} |
|
465 |
return null; |
|
466 |
} |
|
467 |
||
468 |
/** |
|
469 |
* Set the value associated with key. |
|
470 |
* |
|
471 |
* @param key the thread local object |
|
472 |
* @param value the value to be set |
|
473 |
*/ |
|
11275 | 474 |
private void set(ThreadLocal<?> key, Object value) { |
2 | 475 |
|
476 |
// We don't use a fast path as with get() because it is at |
|
477 |
// least as common to use set() to create new entries as |
|
478 |
// it is to replace existing ones, in which case, a fast |
|
479 |
// path would fail more often than not. |
|
480 |
||
481 |
Entry[] tab = table; |
|
482 |
int len = tab.length; |
|
483 |
int i = key.threadLocalHashCode & (len-1); |
|
484 |
||
485 |
for (Entry e = tab[i]; |
|
486 |
e != null; |
|
487 |
e = tab[i = nextIndex(i, len)]) { |
|
11275 | 488 |
ThreadLocal<?> k = e.get(); |
2 | 489 |
|
490 |
if (k == key) { |
|
491 |
e.value = value; |
|
492 |
return; |
|
493 |
} |
|
494 |
||
495 |
if (k == null) { |
|
496 |
replaceStaleEntry(key, value, i); |
|
497 |
return; |
|
498 |
} |
|
499 |
} |
|
500 |
||
501 |
tab[i] = new Entry(key, value); |
|
502 |
int sz = ++size; |
|
503 |
if (!cleanSomeSlots(i, sz) && sz >= threshold) |
|
504 |
rehash(); |
|
505 |
} |
|
506 |
||
507 |
/** |
|
508 |
* Remove the entry for key. |
|
509 |
*/ |
|
11275 | 510 |
private void remove(ThreadLocal<?> key) { |
2 | 511 |
Entry[] tab = table; |
512 |
int len = tab.length; |
|
513 |
int i = key.threadLocalHashCode & (len-1); |
|
514 |
for (Entry e = tab[i]; |
|
515 |
e != null; |
|
516 |
e = tab[i = nextIndex(i, len)]) { |
|
517 |
if (e.get() == key) { |
|
518 |
e.clear(); |
|
519 |
expungeStaleEntry(i); |
|
520 |
return; |
|
521 |
} |
|
522 |
} |
|
523 |
} |
|
524 |
||
525 |
/** |
|
526 |
* Replace a stale entry encountered during a set operation |
|
527 |
* with an entry for the specified key. The value passed in |
|
528 |
* the value parameter is stored in the entry, whether or not |
|
529 |
* an entry already exists for the specified key. |
|
530 |
* |
|
531 |
* As a side effect, this method expunges all stale entries in the |
|
532 |
* "run" containing the stale entry. (A run is a sequence of entries |
|
533 |
* between two null slots.) |
|
534 |
* |
|
535 |
* @param key the key |
|
536 |
* @param value the value to be associated with key |
|
537 |
* @param staleSlot index of the first stale entry encountered while |
|
538 |
* searching for key. |
|
539 |
*/ |
|
11275 | 540 |
private void replaceStaleEntry(ThreadLocal<?> key, Object value, |
2 | 541 |
int staleSlot) { |
542 |
Entry[] tab = table; |
|
543 |
int len = tab.length; |
|
544 |
Entry e; |
|
545 |
||
546 |
// Back up to check for prior stale entry in current run. |
|
547 |
// We clean out whole runs at a time to avoid continual |
|
548 |
// incremental rehashing due to garbage collector freeing |
|
549 |
// up refs in bunches (i.e., whenever the collector runs). |
|
550 |
int slotToExpunge = staleSlot; |
|
551 |
for (int i = prevIndex(staleSlot, len); |
|
552 |
(e = tab[i]) != null; |
|
553 |
i = prevIndex(i, len)) |
|
554 |
if (e.get() == null) |
|
555 |
slotToExpunge = i; |
|
556 |
||
557 |
// Find either the key or trailing null slot of run, whichever |
|
558 |
// occurs first |
|
559 |
for (int i = nextIndex(staleSlot, len); |
|
560 |
(e = tab[i]) != null; |
|
561 |
i = nextIndex(i, len)) { |
|
11275 | 562 |
ThreadLocal<?> k = e.get(); |
2 | 563 |
|
564 |
// If we find key, then we need to swap it |
|
565 |
// with the stale entry to maintain hash table order. |
|
566 |
// The newly stale slot, or any other stale slot |
|
567 |
// encountered above it, can then be sent to expungeStaleEntry |
|
568 |
// to remove or rehash all of the other entries in run. |
|
569 |
if (k == key) { |
|
570 |
e.value = value; |
|
571 |
||
572 |
tab[i] = tab[staleSlot]; |
|
573 |
tab[staleSlot] = e; |
|
574 |
||
575 |
// Start expunge at preceding stale entry if it exists |
|
576 |
if (slotToExpunge == staleSlot) |
|
577 |
slotToExpunge = i; |
|
578 |
cleanSomeSlots(expungeStaleEntry(slotToExpunge), len); |
|
579 |
return; |
|
580 |
} |
|
581 |
||
582 |
// If we didn't find stale entry on backward scan, the |
|
583 |
// first stale entry seen while scanning for key is the |
|
584 |
// first still present in the run. |
|
585 |
if (k == null && slotToExpunge == staleSlot) |
|
586 |
slotToExpunge = i; |
|
587 |
} |
|
588 |
||
589 |
// If key not found, put new entry in stale slot |
|
590 |
tab[staleSlot].value = null; |
|
591 |
tab[staleSlot] = new Entry(key, value); |
|
592 |
||
593 |
// If there are any other stale entries in run, expunge them |
|
594 |
if (slotToExpunge != staleSlot) |
|
595 |
cleanSomeSlots(expungeStaleEntry(slotToExpunge), len); |
|
596 |
} |
|
597 |
||
598 |
/** |
|
599 |
* Expunge a stale entry by rehashing any possibly colliding entries |
|
600 |
* lying between staleSlot and the next null slot. This also expunges |
|
601 |
* any other stale entries encountered before the trailing null. See |
|
602 |
* Knuth, Section 6.4 |
|
603 |
* |
|
604 |
* @param staleSlot index of slot known to have null key |
|
605 |
* @return the index of the next null slot after staleSlot |
|
606 |
* (all between staleSlot and this slot will have been checked |
|
607 |
* for expunging). |
|
608 |
*/ |
|
609 |
private int expungeStaleEntry(int staleSlot) { |
|
610 |
Entry[] tab = table; |
|
611 |
int len = tab.length; |
|
612 |
||
613 |
// expunge entry at staleSlot |
|
614 |
tab[staleSlot].value = null; |
|
615 |
tab[staleSlot] = null; |
|
616 |
size--; |
|
617 |
||
618 |
// Rehash until we encounter null |
|
619 |
Entry e; |
|
620 |
int i; |
|
621 |
for (i = nextIndex(staleSlot, len); |
|
622 |
(e = tab[i]) != null; |
|
623 |
i = nextIndex(i, len)) { |
|
11275 | 624 |
ThreadLocal<?> k = e.get(); |
2 | 625 |
if (k == null) { |
626 |
e.value = null; |
|
627 |
tab[i] = null; |
|
628 |
size--; |
|
629 |
} else { |
|
630 |
int h = k.threadLocalHashCode & (len - 1); |
|
631 |
if (h != i) { |
|
632 |
tab[i] = null; |
|
633 |
||
634 |
// Unlike Knuth 6.4 Algorithm R, we must scan until |
|
635 |
// null because multiple entries could have been stale. |
|
636 |
while (tab[h] != null) |
|
637 |
h = nextIndex(h, len); |
|
638 |
tab[h] = e; |
|
639 |
} |
|
640 |
} |
|
641 |
} |
|
642 |
return i; |
|
643 |
} |
|
644 |
||
645 |
/** |
|
646 |
* Heuristically scan some cells looking for stale entries. |
|
647 |
* This is invoked when either a new element is added, or |
|
648 |
* another stale one has been expunged. It performs a |
|
649 |
* logarithmic number of scans, as a balance between no |
|
650 |
* scanning (fast but retains garbage) and a number of scans |
|
651 |
* proportional to number of elements, that would find all |
|
652 |
* garbage but would cause some insertions to take O(n) time. |
|
653 |
* |
|
654 |
* @param i a position known NOT to hold a stale entry. The |
|
655 |
* scan starts at the element after i. |
|
656 |
* |
|
14770 | 657 |
* @param n scan control: {@code log2(n)} cells are scanned, |
2 | 658 |
* unless a stale entry is found, in which case |
14770 | 659 |
* {@code log2(table.length)-1} additional cells are scanned. |
2 | 660 |
* When called from insertions, this parameter is the number |
661 |
* of elements, but when from replaceStaleEntry, it is the |
|
662 |
* table length. (Note: all this could be changed to be either |
|
663 |
* more or less aggressive by weighting n instead of just |
|
664 |
* using straight log n. But this version is simple, fast, and |
|
665 |
* seems to work well.) |
|
666 |
* |
|
667 |
* @return true if any stale entries have been removed. |
|
668 |
*/ |
|
669 |
private boolean cleanSomeSlots(int i, int n) { |
|
670 |
boolean removed = false; |
|
671 |
Entry[] tab = table; |
|
672 |
int len = tab.length; |
|
673 |
do { |
|
674 |
i = nextIndex(i, len); |
|
675 |
Entry e = tab[i]; |
|
676 |
if (e != null && e.get() == null) { |
|
677 |
n = len; |
|
678 |
removed = true; |
|
679 |
i = expungeStaleEntry(i); |
|
680 |
} |
|
681 |
} while ( (n >>>= 1) != 0); |
|
682 |
return removed; |
|
683 |
} |
|
684 |
||
685 |
/** |
|
686 |
* Re-pack and/or re-size the table. First scan the entire |
|
687 |
* table removing stale entries. If this doesn't sufficiently |
|
688 |
* shrink the size of the table, double the table size. |
|
689 |
*/ |
|
690 |
private void rehash() { |
|
691 |
expungeStaleEntries(); |
|
692 |
||
693 |
// Use lower threshold for doubling to avoid hysteresis |
|
694 |
if (size >= threshold - threshold / 4) |
|
695 |
resize(); |
|
696 |
} |
|
697 |
||
698 |
/** |
|
699 |
* Double the capacity of the table. |
|
700 |
*/ |
|
701 |
private void resize() { |
|
702 |
Entry[] oldTab = table; |
|
703 |
int oldLen = oldTab.length; |
|
704 |
int newLen = oldLen * 2; |
|
705 |
Entry[] newTab = new Entry[newLen]; |
|
706 |
int count = 0; |
|
707 |
||
22581
e868cde95050
8032779: Update code in java.lang to use newer language features
psandoz
parents:
18776
diff
changeset
|
708 |
for (Entry e : oldTab) { |
2 | 709 |
if (e != null) { |
11275 | 710 |
ThreadLocal<?> k = e.get(); |
2 | 711 |
if (k == null) { |
712 |
e.value = null; // Help the GC |
|
713 |
} else { |
|
714 |
int h = k.threadLocalHashCode & (newLen - 1); |
|
715 |
while (newTab[h] != null) |
|
716 |
h = nextIndex(h, newLen); |
|
717 |
newTab[h] = e; |
|
718 |
count++; |
|
719 |
} |
|
720 |
} |
|
721 |
} |
|
722 |
||
723 |
setThreshold(newLen); |
|
724 |
size = count; |
|
725 |
table = newTab; |
|
726 |
} |
|
727 |
||
728 |
/** |
|
729 |
* Expunge all stale entries in the table. |
|
730 |
*/ |
|
731 |
private void expungeStaleEntries() { |
|
732 |
Entry[] tab = table; |
|
733 |
int len = tab.length; |
|
734 |
for (int j = 0; j < len; j++) { |
|
735 |
Entry e = tab[j]; |
|
736 |
if (e != null && e.get() == null) |
|
737 |
expungeStaleEntry(j); |
|
738 |
} |
|
739 |
} |
|
740 |
} |
|
741 |
} |