146 lines
4.6 KiB
Java
146 lines
4.6 KiB
Java
/* java.lang.ref.ReferenceQueue
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Copyright (C) 1999 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.lang.ref;
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/**
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* This is the queue, where references can enqueue themselve on. Each
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* reference may be registered to a queue at initialization time and
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* will be appended to the queue, when the enqueue method is called.
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*
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* The enqueue method may be automatically called by the garbage
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* collector if it detects, that the object is only reachable through
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* the Reference objects.
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*
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* @author Jochen Hoenicke
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* @see Reference#enqueue()
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*/
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public class ReferenceQueue
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{
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/**
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* This is a linked list of references. If this is null, the list is
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* empty. Otherwise this points to the first reference on the queue.
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* The first reference will point to the next reference via the
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* <code>nextOnQueue</code> field. The last reference will point to
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* itself (not to null, since <code>nextOnQueue</code> is used to
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* determine if a reference is enqueued).
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*/
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private Reference first;
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/**
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* Creates a new empty reference queue.
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*/
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public ReferenceQueue()
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{
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}
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/**
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* Checks if there is a reference on the queue, returning it
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* immediately. The reference will be dequeued.
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*
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* @return a reference on the queue, if there is one,
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* <code>null</code> otherwise.
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*/
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public synchronized Reference poll()
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{
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return dequeue();
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}
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/**
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* This is called by reference to enqueue itself on this queue.
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* @param ref the reference that should be enqueued.
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*/
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synchronized void enqueue(Reference ref)
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{
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/* last reference will point to itself */
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ref.nextOnQueue = first == null ? ref : first;
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first = ref;
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/* this wakes only one remove thread. */
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notify();
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}
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/**
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* Remove a reference from the queue, if there is one.
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* @return the first element of the queue, or null if there isn't any.
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*/
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private Reference dequeue()
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{
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if (first == null)
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return null;
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Reference result = first;
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first = (first == first.nextOnQueue) ? null : first.nextOnQueue;
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result.nextOnQueue = null;
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return result;
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}
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/**
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* Removes a reference from the queue, blocking for <code>timeout</code>
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* until a reference is enqueued.
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* @param timeout the timeout period in milliseconds, <code>0</code> means
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* wait forever.
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* @return the reference removed from the queue, or
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* <code>null</code> if timeout period expired.
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* @exception InterruptedException if the wait was interrupted.
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*/
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public synchronized Reference remove(long timeout)
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throws InterruptedException
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{
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if (first == null)
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{
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wait(timeout);
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}
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return dequeue();
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}
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/**
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* Removes a reference from the queue, blocking until a reference is
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* enqueued.
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*
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* @return the reference removed from the queue.
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* @exception InterruptedException if the wait was interrupted.
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*/
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public Reference remove()
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throws InterruptedException
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{
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return remove(0L);
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}
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}
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