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/*
* Copyright (c) 2008, 2011, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code 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
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package sun.nio.fs;
import java.nio.file.*;
import java.util.concurrent.*;
import java.io.IOException;
/**
* Base implementation class for watch services.
*/
abstract class AbstractWatchService implements WatchService {
// signaled keys waiting to be dequeued
private final LinkedBlockingDeque<WatchKey> pendingKeys =
new LinkedBlockingDeque<WatchKey>();
// special key to indicate that watch service is closed
private final WatchKey CLOSE_KEY =
new AbstractWatchKey(null, null) {
@Override
public boolean isValid() {
return true;
}
@Override
public void cancel() {
}
};
// used when closing watch service
private volatile boolean closed;
private final Object closeLock = new Object();
protected AbstractWatchService() {
}
/**
* Register the given object with this watch service
*/
abstract WatchKey register(Path path,
WatchEvent.Kind<?>[] events,
WatchEvent.Modifier... modifers)
throws IOException;
// used by AbstractWatchKey to enqueue key
final void enqueueKey(WatchKey key) {
pendingKeys.offer(key);
}
/**
* Throws ClosedWatchServiceException if watch service is closed
*/
private void checkOpen() {
if (closed)
throw new ClosedWatchServiceException();
}
/**
* Checks the key isn't the special CLOSE_KEY used to unblock threads when
* the watch service is closed.
*/
private void checkKey(WatchKey key) {
if (key == CLOSE_KEY) {
// re-queue in case there are other threads blocked in take/poll
enqueueKey(key);
}
checkOpen();
}
@Override
public final WatchKey poll() {
checkOpen();
WatchKey key = pendingKeys.poll();
checkKey(key);
return key;
}
@Override
public final WatchKey poll(long timeout, TimeUnit unit)
throws InterruptedException
{
checkOpen();
WatchKey key = pendingKeys.poll(timeout, unit);
checkKey(key);
return key;
}
@Override
public final WatchKey take()
throws InterruptedException
{
checkOpen();
WatchKey key = pendingKeys.take();
checkKey(key);
return key;
}
/**
* Tells whether or not this watch service is open.
*/
final boolean isOpen() {
return !closed;
}
/**
* Retrieves the object upon which the close method synchronizes.
*/
final Object closeLock() {
return closeLock;
}
/**
* Closes this watch service. This method is invoked by the close
* method to perform the actual work of closing the watch service.
*/
abstract void implClose() throws IOException;
@Override
public final void close()
throws IOException
{
synchronized (closeLock) {
// nothing to do if already closed
if (closed)
return;
closed = true;
implClose();
// clear pending keys and queue special key to ensure that any
// threads blocked in take/poll wakeup
pendingKeys.clear();
pendingKeys.offer(CLOSE_KEY);
}
}
}
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