org.openide.util.TimedSoftReference Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.openide.util;
import java.lang.ref.SoftReference;
import java.util.Map;
/**
* A soft reference which is held strongly for a while after last access.
* Lifecycle:
*
* - Created. Referent held strongly. A task is scheduled into the request
* processor for some time in the future (currently 30 seconds).
* - Expired. After the timeout, the reference switches to a normal soft
* reference.
* - Touched. If the value is accessed before it is garbage collected,
* whether the reference is expired or not, the reference is "touched".
* This means that the referent is again held strongly and the timeout
* is started from scratch.
* - Dead. If after expiry there is no access before the next full GC cycle,
* the GC algorithm may reclaim the reference. In this case the reference
* of course dies. As a bonus, it will try to remove itself as the value
* from a map of your choice, to make it convenient to use these references
* as values in a caching map without leaking memory for the key.
*
* @author Jesse Glick
*/
final class TimedSoftReference extends SoftReference implements Runnable {
private static final int TIMEOUT = 30000;
private static final RequestProcessor RP = new RequestProcessor("TimedSoftReference"); // NOI18N
private RequestProcessor.Task task;
private T o;
private final Map m;
private final Object k;
/** Time when the object was last time touched */
private long touched;
/**
* Create a soft reference with timeout.
* The supplied map serves double duty as a synchronization lock
* for the reference's state changes.
* @param o the referent
* @param m a map in which this reference may serve as a value
* @param k the key whose value in m may be this reference
*/
public TimedSoftReference(T o, Map m, Object k) {
super(o, BaseUtilities.activeReferenceQueue());
this.o = o;
this.m = m;
this.k = k;
task = RP.create(this);
task.schedule(TIMEOUT);
}
public void run() {
synchronized (m) {
if (o != null) {
//System.err.println("Expire " + k);
// how long we've really been idle
long unused = System.currentTimeMillis() - touched;
if (unused > (TIMEOUT / 2)) {
o = null;
touched = 0;
} else {
task.schedule(TIMEOUT - (int) unused);
}
} else {
// clean up map ref, we are dead
//System.err.println("Die " + k);
m.remove(k);
}
}
}
public T get() {
synchronized (m) {
if (o == null) {
o = super.get();
}
if (o != null) {
// touch me
//System.err.println("Touch " + k);
if (touched == 0) {
task.schedule(TIMEOUT);
}
touched = System.currentTimeMillis();
return o;
} else {
return null;
}
}
}
}