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author | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
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committer | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
commit | 554fd8c5195424bdbcabf5de30fdc183aba391bd (patch) | |
tree | 976dc5ab7fddf506dadce60ae936f43f58787092 /libjava/classpath/java/lang/ref/ReferenceQueue.java | |
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Diffstat (limited to 'libjava/classpath/java/lang/ref/ReferenceQueue.java')
-rw-r--r-- | libjava/classpath/java/lang/ref/ReferenceQueue.java | 164 |
1 files changed, 164 insertions, 0 deletions
diff --git a/libjava/classpath/java/lang/ref/ReferenceQueue.java b/libjava/classpath/java/lang/ref/ReferenceQueue.java new file mode 100644 index 000000000..73f62d64a --- /dev/null +++ b/libjava/classpath/java/lang/ref/ReferenceQueue.java @@ -0,0 +1,164 @@ +/* java.lang.ref.ReferenceQueue + Copyright (C) 1999, 2004, 2006 Free Software Foundation, Inc. + +This file is part of GNU Classpath. + +GNU Classpath is free software; you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation; either version 2, or (at your option) +any later version. + +GNU Classpath is distributed in the hope that it will be useful, but +WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +General Public License for more details. + +You should have received a copy of the GNU General Public License +along with GNU Classpath; see the file COPYING. If not, write to the +Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA +02110-1301 USA. + +Linking this library statically or dynamically with other modules is +making a combined work based on this library. Thus, the terms and +conditions of the GNU General Public License cover the whole +combination. + +As a special exception, the copyright holders of this library give you +permission to link this library with independent modules to produce an +executable, regardless of the license terms of these independent +modules, and to copy and distribute the resulting executable under +terms of your choice, provided that you also meet, for each linked +independent module, the terms and conditions of the license of that +module. An independent module is a module which is not derived from +or based on this library. If you modify this library, you may extend +this exception to your version of the library, but you are not +obligated to do so. If you do not wish to do so, delete this +exception statement from your version. */ + + +package java.lang.ref; + +/** + * This is the queue, where references can enqueue themselve on. Each + * reference may be registered to a queue at initialization time and + * will be appended to the queue, when the enqueue method is called. + * + * The enqueue method may be automatically called by the garbage + * collector if it detects, that the object is only reachable through + * the Reference objects. + * + * @author Jochen Hoenicke + * @see Reference#enqueue() + */ +public class ReferenceQueue<T> +{ + /** + * This is a linked list of references. If this is null, the list is + * empty. Otherwise this points to the first reference on the queue. + * The first reference will point to the next reference via the + * <code>nextOnQueue</code> field. The last reference will point to + * itself (not to null, since <code>nextOnQueue</code> is used to + * determine if a reference is enqueued). + */ + private Reference<? extends T> first; + + /** + * This is the lock that protects our linked list and is used to signal + * a thread waiting in remove(). + */ + private final Object lock = new Object(); + + /** + * Creates a new empty reference queue. + */ + public ReferenceQueue() + { + } + + /** + * Checks if there is a reference on the queue, returning it + * immediately. The reference will be dequeued. + * + * @return a reference on the queue, if there is one, + * <code>null</code> otherwise. + */ + public Reference<? extends T> poll() + { + return dequeue(); + } + + /** + * This is called by reference to enqueue itself on this queue. + * @param ref the reference that should be enqueued. + * @return true if successful, false if not. + */ + final boolean enqueue(Reference<? extends T> ref) + { + synchronized (lock) + { + if (ref.queue != this) + return false; + + /* last reference will point to itself */ + ref.nextOnQueue = first == null ? ref : first; + ref.queue = null; + first = ref; + /* this wakes only one remove thread. */ + lock.notify(); + return true; + } + } + + /** + * Remove a reference from the queue, if there is one. + * @return the first element of the queue, or null if there isn't any. + */ + private Reference<? extends T> dequeue() + { + synchronized (lock) + { + if (first == null) + return null; + + Reference<? extends T> result = first; + first = (first == first.nextOnQueue) ? null : first.nextOnQueue; + result.nextOnQueue = null; + return result; + } + } + + /** + * Removes a reference from the queue, blocking for <code>timeout</code> + * until a reference is enqueued. + * @param timeout the timeout period in milliseconds, <code>0</code> means + * wait forever. + * @return the reference removed from the queue, or + * <code>null</code> if timeout period expired. + * @exception InterruptedException if the wait was interrupted. + */ + public Reference<? extends T> remove(long timeout) + throws InterruptedException + { + synchronized (lock) + { + if (first == null) + lock.wait(timeout); + } + + return dequeue(); + } + + + /** + * Removes a reference from the queue, blocking until a reference is + * enqueued. + * + * @return the reference removed from the queue. + * @exception InterruptedException if the wait was interrupted. + */ + public Reference<? extends T> remove() + throws InterruptedException + { + return remove(0L); + } +} |