author | ihse |
Fri, 12 Jun 2015 08:31:01 +0200 | |
changeset 33957 | 39113ae98993 |
parent 29986 | 97167d851fc4 |
child 32649 | 2ee9017c7597 |
permissions | -rw-r--r-- |
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/* |
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* Copyright (c) 2003, 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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package sun.misc; |
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import java.lang.ref.*; |
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import java.security.AccessController; |
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import java.security.PrivilegedAction; |
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/** |
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* General-purpose phantom-reference-based cleaners. |
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* |
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* <p> Cleaners are a lightweight and more robust alternative to finalization. |
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* They are lightweight because they are not created by the VM and thus do not |
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* require a JNI upcall to be created, and because their cleanup code is |
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* invoked directly by the reference-handler thread rather than by the |
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* finalizer thread. They are more robust because they use phantom references, |
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* the weakest type of reference object, thereby avoiding the nasty ordering |
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* problems inherent to finalization. |
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* |
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* <p> A cleaner tracks a referent object and encapsulates a thunk of arbitrary |
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* cleanup code. Some time after the GC detects that a cleaner's referent has |
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* become phantom-reachable, the reference-handler thread will run the cleaner. |
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* Cleaners may also be invoked directly; they are thread safe and ensure that |
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* they run their thunks at most once. |
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* |
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* <p> Cleaners are not a replacement for finalization. They should be used |
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* only when the cleanup code is extremely simple and straightforward. |
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* Nontrivial cleaners are inadvisable since they risk blocking the |
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* reference-handler thread and delaying further cleanup and finalization. |
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* |
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* |
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* @author Mark Reinhold |
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*/ |
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public class Cleaner |
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extends PhantomReference<Object> |
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{ |
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// Dummy reference queue, needed because the PhantomReference constructor |
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// insists that we pass a queue. Nothing will ever be placed on this queue |
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// since the reference handler invokes cleaners explicitly. |
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// |
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private static final ReferenceQueue<Object> dummyQueue = new ReferenceQueue<>(); |
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// Doubly-linked list of live cleaners, which prevents the cleaners |
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// themselves from being GC'd before their referents |
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// |
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static private Cleaner first = null; |
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private Cleaner |
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next = null, |
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prev = null; |
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private static synchronized Cleaner add(Cleaner cl) { |
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if (first != null) { |
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cl.next = first; |
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first.prev = cl; |
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} |
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first = cl; |
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return cl; |
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} |
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private static synchronized boolean remove(Cleaner cl) { |
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// If already removed, do nothing |
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if (cl.next == cl) |
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return false; |
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// Update list |
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if (first == cl) { |
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if (cl.next != null) |
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first = cl.next; |
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else |
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first = cl.prev; |
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} |
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if (cl.next != null) |
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cl.next.prev = cl.prev; |
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if (cl.prev != null) |
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cl.prev.next = cl.next; |
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// Indicate removal by pointing the cleaner to itself |
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cl.next = cl; |
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cl.prev = cl; |
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return true; |
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} |
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private final Runnable thunk; |
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private Cleaner(Object referent, Runnable thunk) { |
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super(referent, dummyQueue); |
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this.thunk = thunk; |
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} |
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/** |
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* Creates a new cleaner. |
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* |
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* @param ob the referent object to be cleaned |
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* @param thunk |
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* The cleanup code to be run when the cleaner is invoked. The |
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* cleanup code is run directly from the reference-handler thread, |
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* so it should be as simple and straightforward as possible. |
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* |
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* @return The new cleaner |
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*/ |
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public static Cleaner create(Object ob, Runnable thunk) { |
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if (thunk == null) |
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return null; |
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return add(new Cleaner(ob, thunk)); |
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} |
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/** |
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* Runs this cleaner, if it has not been run before. |
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*/ |
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public void clean() { |
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if (!remove(this)) |
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return; |
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try { |
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thunk.run(); |
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} catch (final Throwable x) { |
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AccessController.doPrivileged(new PrivilegedAction<>() { |
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public Void run() { |
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if (System.err != null) |
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new Error("Cleaner terminated abnormally", x) |
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.printStackTrace(); |
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System.exit(1); |
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return null; |
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}}); |
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} |
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} |
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} |