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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
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* Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
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* The contents of this file are subject to the terms of either the GNU
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* General Public License Version 2 only ("GPL") or the Common
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* Development and Distribution License("CDDL") (collectively, the
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* "License"). You may not use this file except in compliance with the
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* License. You can obtain a copy of the License at
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* http://www.netbeans.org/cddl-gplv2.html
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* or nbbuild/licenses/CDDL-GPL-2-CP. See the License for the
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* specific language governing permissions and limitations under the
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* License. When distributing the software, include this License Header
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* Notice in each file and include the License file at
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* nbbuild/licenses/CDDL-GPL-2-CP. Sun designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Sun in the GPL Version 2 section of the License file that
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* accompanied this code. If applicable, add the following below the
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* License Header, with the fields enclosed by brackets [] replaced by
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* your own identifying information:
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* "Portions Copyrighted [year] [name of copyright owner]"
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* The Original Software is NetBeans. The Initial Developer of the Original
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* Software is Sun Microsystems, Inc. Portions Copyright 1997-2006 Sun
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* Microsystems, Inc. All Rights Reserved.
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* If you wish your version of this file to be governed by only the CDDL
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* or only the GPL Version 2, indicate your decision by adding
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* "[Contributor] elects to include this software in this distribution
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* under the [CDDL or GPL Version 2] license." If you do not indicate a
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* single choice of license, a recipient has the option to distribute
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* your version of this file under either the CDDL, the GPL Version 2 or
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* to extend the choice of license to its licensees as provided above.
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* However, if you add GPL Version 2 code and therefore, elected the GPL
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* Version 2 license, then the option applies only if the new code is
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* made subject to such option by the copyright holder.
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package org.netbeans.modules.projectapi;
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// XXX COPIED from org.openide.util w/ changes:
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// removed map key functionality
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import java.lang.ref.WeakReference;
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import org.openide.util.RequestProcessor;
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import org.openide.util.Utilities;
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* A weak reference which is held strongly for a while after last access.
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* <li>Created. Referent held strongly. A task is scheduled into the request
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* processor for some time in the future (currently 15 seconds).</li>
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* <li>Expired. After the timeout, the reference switches to a normal weak
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* <li>Touched. If the value is accessed before it is garbage collected,
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* whether the reference is expired or not, the reference is "touched".
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* This means that the referent is again held strongly and the timeout
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* is started from scratch.</li>
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* <li>Dead. If after expiry there is no access before the next full GC cycle,
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* the GC algorithm may reclaim the reference. In this case the reference
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* of course dies.</li>
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public final class TimedWeakReference<T> extends WeakReference<T> implements Runnable {
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public static int TIMEOUT = 15000;
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private static final RequestProcessor RP = new RequestProcessor("TimedWeakReference"); // NOI18N
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private RequestProcessor.Task task;
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/** Time when the object was last time touched */
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* Create a weak reference with timeout.
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* @param o the referent
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public TimedWeakReference(T o) {
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super(o, Utilities.activeReferenceQueue());
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task = RP.create(this);
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task.schedule(TIMEOUT);
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public synchronized void run() {
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//System.err.println("Expire " + k);
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// how long we've really been idle
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long unused = System.currentTimeMillis() - touched;
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if (unused > TIMEOUT / 2) {
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task.schedule(TIMEOUT - (int) unused);
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public synchronized T get() {
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//System.err.println("Touch " + k);
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task.schedule(TIMEOUT);
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touched = System.currentTimeMillis();