| /* |
| * 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 jdk.internal.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(null, task, "NIO-Task", 0, false); |
| 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); |
| } |
| } |