893N/A/*
2362N/A * Copyright (c) 2008, 2009, Oracle and/or its affiliates. All rights reserved.
893N/A * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
893N/A *
893N/A * This code is free software; you can redistribute it and/or modify it
893N/A * under the terms of the GNU General Public License version 2 only, as
2362N/A * published by the Free Software Foundation. Oracle designates this
893N/A * particular file as subject to the "Classpath" exception as provided
2362N/A * by Oracle in the LICENSE file that accompanied this code.
893N/A *
893N/A * This code is distributed in the hope that it will be useful, but WITHOUT
893N/A * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
893N/A * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
893N/A * version 2 for more details (a copy is included in the LICENSE file that
893N/A * accompanied this code).
893N/A *
893N/A * You should have received a copy of the GNU General Public License version
893N/A * 2 along with this work; if not, write to the Free Software Foundation,
893N/A * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
893N/A *
2362N/A * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
2362N/A * or visit www.oracle.com if you need additional information or have any
2362N/A * questions.
893N/A */
893N/A
893N/Apackage sun.nio.fs;
893N/A
893N/Aimport sun.misc.Unsafe;
893N/Aimport java.util.concurrent.ExecutionException;
893N/A
893N/A/**
893N/A * Base implementation of a task (typically native) that polls a memory location
893N/A * during execution so that it may be aborted/cancelled before completion. The
893N/A * task is executed by invoking the {@link runInterruptibly} method defined
893N/A * here and cancelled by invoking Thread.interrupt.
893N/A */
893N/A
893N/Aabstract class Cancellable implements Runnable {
893N/A private static final Unsafe unsafe = Unsafe.getUnsafe();
893N/A
893N/A private final long pollingAddress;
893N/A private final Object lock = new Object();
893N/A
893N/A // the following require lock when examining or changing
893N/A private boolean completed;
893N/A private Throwable exception;
893N/A
893N/A protected Cancellable() {
893N/A pollingAddress = unsafe.allocateMemory(4);
893N/A unsafe.putIntVolatile(null, pollingAddress, 0);
893N/A }
893N/A
893N/A /**
893N/A * Returns the memory address of a 4-byte int that should be polled to
893N/A * detect cancellation.
893N/A */
893N/A protected long addressToPollForCancel() {
893N/A return pollingAddress;
893N/A }
893N/A
893N/A /**
893N/A * The value to write to the polled memory location to indicate that the
893N/A * task has been cancelled. If this method is not overridden then it
893N/A * defaults to MAX_VALUE.
893N/A */
893N/A protected int cancelValue() {
893N/A return Integer.MAX_VALUE;
893N/A }
893N/A
893N/A /**
893N/A * "cancels" the task by writing bits into memory location that it polled
893N/A * by the task.
893N/A */
893N/A final void cancel() {
893N/A synchronized (lock) {
893N/A if (!completed) {
893N/A unsafe.putIntVolatile(null, pollingAddress, cancelValue());
893N/A }
893N/A }
893N/A }
893N/A
893N/A /**
893N/A * Returns the exception thrown by the task or null if the task completed
893N/A * successfully.
893N/A */
893N/A private Throwable exception() {
893N/A synchronized (lock) {
893N/A return exception;
893N/A }
893N/A }
893N/A
893N/A @Override
893N/A public final void run() {
893N/A try {
893N/A implRun();
893N/A } catch (Throwable t) {
893N/A synchronized (lock) {
893N/A exception = t;
893N/A }
893N/A } finally {
893N/A synchronized (lock) {
893N/A completed = true;
893N/A unsafe.freeMemory(pollingAddress);
893N/A }
893N/A }
893N/A }
893N/A
893N/A /**
893N/A * The task body. This should periodically poll the memory location
893N/A * to check for cancellation.
893N/A */
893N/A abstract void implRun() throws Throwable;
893N/A
893N/A /**
893N/A * Invokes the given task in its own thread. If this (meaning the current)
893N/A * thread is interrupted then an attempt is make to cancel the background
893N/A * thread by writing into the memory location that it polls cooperatively.
893N/A */
893N/A static void runInterruptibly(Cancellable task) throws ExecutionException {
893N/A Thread t = new Thread(task);
893N/A t.start();
893N/A boolean cancelledByInterrupt = false;
893N/A while (t.isAlive()) {
893N/A try {
893N/A t.join();
893N/A } catch (InterruptedException e) {
893N/A cancelledByInterrupt = true;
893N/A task.cancel();
893N/A }
893N/A }
893N/A if (cancelledByInterrupt)
893N/A Thread.currentThread().interrupt();
893N/A Throwable exc = task.exception();
893N/A if (exc != null)
893N/A throw new ExecutionException(exc);
893N/A }
893N/A}