138 lines
4.4 KiB
Java
138 lines
4.4 KiB
Java
/*
|
|
* Copyright (c) 2008, 2009, 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 sun.misc.Unsafe;
|
|
import java.util.concurrent.ExecutionException;
|
|
|
|
/**
|
|
* Base implementation of a task (typically native) that polls a memory location
|
|
* during execution so that it may be aborted/cancelled before completion. The
|
|
* task is executed by invoking the {@link runInterruptibly} method defined
|
|
* here and cancelled by invoking Thread.interrupt.
|
|
*/
|
|
|
|
abstract class Cancellable implements Runnable {
|
|
private static final Unsafe unsafe = Unsafe.getUnsafe();
|
|
|
|
private final long pollingAddress;
|
|
private final Object lock = new Object();
|
|
|
|
// the following require lock when examining or changing
|
|
private boolean completed;
|
|
private Throwable exception;
|
|
|
|
protected Cancellable() {
|
|
pollingAddress = unsafe.allocateMemory(4);
|
|
unsafe.putIntVolatile(null, pollingAddress, 0);
|
|
}
|
|
|
|
/**
|
|
* Returns the memory address of a 4-byte int that should be polled to
|
|
* detect cancellation.
|
|
*/
|
|
protected long addressToPollForCancel() {
|
|
return pollingAddress;
|
|
}
|
|
|
|
/**
|
|
* The value to write to the polled memory location to indicate that the
|
|
* task has been cancelled. If this method is not overridden then it
|
|
* defaults to MAX_VALUE.
|
|
*/
|
|
protected int cancelValue() {
|
|
return Integer.MAX_VALUE;
|
|
}
|
|
|
|
/**
|
|
* "cancels" the task by writing bits into memory location that it polled
|
|
* by the task.
|
|
*/
|
|
final void cancel() {
|
|
synchronized (lock) {
|
|
if (!completed) {
|
|
unsafe.putIntVolatile(null, pollingAddress, cancelValue());
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Returns the exception thrown by the task or null if the task completed
|
|
* successfully.
|
|
*/
|
|
private Throwable exception() {
|
|
synchronized (lock) {
|
|
return exception;
|
|
}
|
|
}
|
|
|
|
@Override
|
|
public final void run() {
|
|
try {
|
|
implRun();
|
|
} catch (Throwable t) {
|
|
synchronized (lock) {
|
|
exception = t;
|
|
}
|
|
} finally {
|
|
synchronized (lock) {
|
|
completed = true;
|
|
unsafe.freeMemory(pollingAddress);
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* The task body. This should periodically poll the memory location
|
|
* to check for cancellation.
|
|
*/
|
|
abstract void implRun() throws Throwable;
|
|
|
|
/**
|
|
* Invokes the given task in its own thread. If this (meaning the current)
|
|
* thread is interrupted then an attempt is make to cancel the background
|
|
* thread by writing into the memory location that it polls cooperatively.
|
|
*/
|
|
static void runInterruptibly(Cancellable task) throws ExecutionException {
|
|
Thread t = new Thread(task);
|
|
t.start();
|
|
boolean cancelledByInterrupt = false;
|
|
while (t.isAlive()) {
|
|
try {
|
|
t.join();
|
|
} catch (InterruptedException e) {
|
|
cancelledByInterrupt = true;
|
|
task.cancel();
|
|
}
|
|
}
|
|
if (cancelledByInterrupt)
|
|
Thread.currentThread().interrupt();
|
|
Throwable exc = task.exception();
|
|
if (exc != null)
|
|
throw new ExecutionException(exc);
|
|
}
|
|
}
|