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SharedCloseable.java
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86 lines (75 loc) · 2.39 KB
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package soot.util;
/*-
* #%L
* Soot - a J*va Optimization Framework
* %%
* Copyright (C) 2004 Ondrej Lhotak
* %%
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation, either version 2.1 of the
* License, or (at your option) any later version.
*
* This program 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 Lesser Public License for more details.
*
* You should have received a copy of the GNU General Lesser Public
* License along with this program. If not, see
* <http://www.gnu.org/licenses/lgpl-2.1.html>.
* #L%
*/
import java.io.Closeable;
import java.io.IOException;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
/**
* Reference counting wrapper for a {@link Closeable} that closes the resource when the reference count reaches {@code 0}.
* Extends {@link AutoCloseable} so that each region using the resource can simply be wrapped in a try-with-resources block.
*
* @author Timothy Hoffman
*
* @param <T>
*
* @see AutoCloseable
*/
public final class SharedCloseable<T extends Closeable> implements AutoCloseable {
private static final AtomicLongFieldUpdater<SharedCloseable> NUM_REFS_UPDATER
= AtomicLongFieldUpdater.newUpdater(SharedCloseable.class, "numRefs");
// NOTE: only accessed via the AtomicLongFieldUpdater
private volatile long numRefs = 1;
private final T resource;
public SharedCloseable(T resource) {
this.resource = resource;
}
public SharedCloseable<T> acquire() {
long oldCount = NUM_REFS_UPDATER.getAndIncrement(this);
if (oldCount <= 0) {
NUM_REFS_UPDATER.getAndDecrement(this);// restore to 0 (or lower)
throw new IllegalStateException("Already closed");
}
return this;
}
public boolean release() {
long newCount = NUM_REFS_UPDATER.decrementAndGet(this);
if (newCount == 0) {
try {
resource.close();
} catch (IOException ex) {
// ignored
}
return true;
} else if (newCount < 0) {
throw new IllegalStateException("Already closed");
} else {
return false;
}
}
public T get() {
return resource;
}
@Override
public void close() {
release();
}
}