| /* |
| * Written by Doug Lea with assistance from members of JCP JSR-166 |
| * Expert Group and released to the public domain, as explained at |
| * http://creativecommons.org/licenses/publicdomain |
| */ |
| |
| package java.util.concurrent; |
| import java.util.concurrent.locks.*; |
| |
| /** |
| * A cancellable asynchronous computation. This class provides a base |
| * implementation of {@link Future}, with methods to start and cancel |
| * a computation, query to see if the computation is complete, and |
| * retrieve the result of the computation. The result can only be |
| * retrieved when the computation has completed; the <tt>get</tt> |
| * method will block if the computation has not yet completed. Once |
| * the computation has completed, the computation cannot be restarted |
| * or cancelled. |
| * |
| * <p>A <tt>FutureTask</tt> can be used to wrap a {@link Callable} or |
| * {@link java.lang.Runnable} object. Because <tt>FutureTask</tt> |
| * implements <tt>Runnable</tt>, a <tt>FutureTask</tt> can be |
| * submitted to an {@link Executor} for execution. |
| * |
| * <p>In addition to serving as a standalone class, this class provides |
| * <tt>protected</tt> functionality that may be useful when creating |
| * customized task classes. |
| * |
| * @since 1.5 |
| * @author Doug Lea |
| * @param <V> The result type returned by this FutureTask's <tt>get</tt> method |
| */ |
| public class FutureTask<V> implements Future<V>, Runnable { |
| /** Synchronization control for FutureTask */ |
| private final Sync sync; |
| |
| /** |
| * Creates a <tt>FutureTask</tt> that will, upon running, execute the |
| * given <tt>Callable</tt>. |
| * |
| * @param callable the callable task |
| * @throws NullPointerException if callable is null |
| */ |
| public FutureTask(Callable<V> callable) { |
| if (callable == null) |
| throw new NullPointerException(); |
| sync = new Sync(callable); |
| } |
| |
| /** |
| * Creates a <tt>FutureTask</tt> that will, upon running, execute the |
| * given <tt>Runnable</tt>, and arrange that <tt>get</tt> will return the |
| * given result on successful completion. |
| * |
| * @param runnable the runnable task |
| * @param result the result to return on successful completion. If |
| * you don't need a particular result, consider using |
| * constructions of the form: |
| * <tt>Future<?> f = new FutureTask<Object>(runnable, null)</tt> |
| * @throws NullPointerException if runnable is null |
| */ |
| public FutureTask(Runnable runnable, V result) { |
| sync = new Sync(Executors.callable(runnable, result)); |
| } |
| |
| public boolean isCancelled() { |
| return sync.innerIsCancelled(); |
| } |
| |
| public boolean isDone() { |
| return sync.innerIsDone(); |
| } |
| |
| public boolean cancel(boolean mayInterruptIfRunning) { |
| return sync.innerCancel(mayInterruptIfRunning); |
| } |
| |
| /** |
| * @throws CancellationException {@inheritDoc} |
| */ |
| public V get() throws InterruptedException, ExecutionException { |
| return sync.innerGet(); |
| } |
| |
| /** |
| * @throws CancellationException {@inheritDoc} |
| */ |
| public V get(long timeout, TimeUnit unit) |
| throws InterruptedException, ExecutionException, TimeoutException { |
| return sync.innerGet(unit.toNanos(timeout)); |
| } |
| |
| /** |
| * Protected method invoked when this task transitions to state |
| * <tt>isDone</tt> (whether normally or via cancellation). The |
| * default implementation does nothing. Subclasses may override |
| * this method to invoke completion callbacks or perform |
| * bookkeeping. Note that you can query status inside the |
| * implementation of this method to determine whether this task |
| * has been cancelled. |
| */ |
| protected void done() { } |
| |
| /** |
| * Sets the result of this Future to the given value unless |
| * this future has already been set or has been cancelled. |
| * This method is invoked internally by the <tt>run</tt> method |
| * upon successful completion of the computation. |
| * @param v the value |
| */ |
| protected void set(V v) { |
| sync.innerSet(v); |
| } |
| |
| /** |
| * Causes this future to report an <tt>ExecutionException</tt> |
| * with the given throwable as its cause, unless this Future has |
| * already been set or has been cancelled. |
| * This method is invoked internally by the <tt>run</tt> method |
| * upon failure of the computation. |
| * @param t the cause of failure |
| */ |
| protected void setException(Throwable t) { |
| sync.innerSetException(t); |
| } |
| |
| // The following (duplicated) doc comment can be removed once |
| // |
| // 6270645: Javadoc comments should be inherited from most derived |
| // superinterface or superclass |
| // is fixed. |
| /** |
| * Sets this Future to the result of its computation |
| * unless it has been cancelled. |
| */ |
| public void run() { |
| sync.innerRun(); |
| } |
| |
| /** |
| * Executes the computation without setting its result, and then |
| * resets this Future to initial state, failing to do so if the |
| * computation encounters an exception or is cancelled. This is |
| * designed for use with tasks that intrinsically execute more |
| * than once. |
| * @return true if successfully run and reset |
| */ |
| protected boolean runAndReset() { |
| return sync.innerRunAndReset(); |
| } |
| |
| /** |
| * Synchronization control for FutureTask. Note that this must be |
| * a non-static inner class in order to invoke the protected |
| * <tt>done</tt> method. For clarity, all inner class support |
| * methods are same as outer, prefixed with "inner". |
| * |
| * Uses AQS sync state to represent run status |
| */ |
| private final class Sync extends AbstractQueuedSynchronizer { |
| private static final long serialVersionUID = -7828117401763700385L; |
| |
| /** State value representing that task is ready to run */ |
| private static final int READY = 0; |
| /** State value representing that task is running */ |
| private static final int RUNNING = 1; |
| /** State value representing that task ran */ |
| private static final int RAN = 2; |
| /** State value representing that task was cancelled */ |
| private static final int CANCELLED = 4; |
| |
| /** The underlying callable */ |
| private final Callable<V> callable; |
| /** The result to return from get() */ |
| private V result; |
| /** The exception to throw from get() */ |
| private Throwable exception; |
| |
| /** |
| * The thread running task. When nulled after set/cancel, this |
| * indicates that the results are accessible. Must be |
| * volatile, to ensure visibility upon completion. |
| */ |
| private volatile Thread runner; |
| |
| Sync(Callable<V> callable) { |
| this.callable = callable; |
| } |
| |
| private boolean ranOrCancelled(int state) { |
| return (state & (RAN | CANCELLED)) != 0; |
| } |
| |
| /** |
| * Implements AQS base acquire to succeed if ran or cancelled |
| */ |
| protected int tryAcquireShared(int ignore) { |
| return innerIsDone() ? 1 : -1; |
| } |
| |
| /** |
| * Implements AQS base release to always signal after setting |
| * final done status by nulling runner thread. |
| */ |
| protected boolean tryReleaseShared(int ignore) { |
| runner = null; |
| return true; |
| } |
| |
| boolean innerIsCancelled() { |
| return getState() == CANCELLED; |
| } |
| |
| boolean innerIsDone() { |
| return ranOrCancelled(getState()) && runner == null; |
| } |
| |
| V innerGet() throws InterruptedException, ExecutionException { |
| acquireSharedInterruptibly(0); |
| if (getState() == CANCELLED) |
| throw new CancellationException(); |
| if (exception != null) |
| throw new ExecutionException(exception); |
| return result; |
| } |
| |
| V innerGet(long nanosTimeout) throws InterruptedException, ExecutionException, TimeoutException { |
| if (!tryAcquireSharedNanos(0, nanosTimeout)) |
| throw new TimeoutException(); |
| if (getState() == CANCELLED) |
| throw new CancellationException(); |
| if (exception != null) |
| throw new ExecutionException(exception); |
| return result; |
| } |
| |
| void innerSet(V v) { |
| for (;;) { |
| int s = getState(); |
| if (s == RAN) |
| return; |
| if (s == CANCELLED) { |
| // aggressively release to set runner to null, |
| // in case we are racing with a cancel request |
| // that will try to interrupt runner |
| releaseShared(0); |
| return; |
| } |
| if (compareAndSetState(s, RAN)) { |
| result = v; |
| releaseShared(0); |
| done(); |
| return; |
| } |
| } |
| } |
| |
| void innerSetException(Throwable t) { |
| for (;;) { |
| int s = getState(); |
| if (s == RAN) |
| return; |
| if (s == CANCELLED) { |
| // aggressively release to set runner to null, |
| // in case we are racing with a cancel request |
| // that will try to interrupt runner |
| releaseShared(0); |
| return; |
| } |
| if (compareAndSetState(s, RAN)) { |
| exception = t; |
| releaseShared(0); |
| done(); |
| return; |
| } |
| } |
| } |
| |
| boolean innerCancel(boolean mayInterruptIfRunning) { |
| for (;;) { |
| int s = getState(); |
| if (ranOrCancelled(s)) |
| return false; |
| if (compareAndSetState(s, CANCELLED)) |
| break; |
| } |
| if (mayInterruptIfRunning) { |
| Thread r = runner; |
| if (r != null) |
| r.interrupt(); |
| } |
| releaseShared(0); |
| done(); |
| return true; |
| } |
| |
| void innerRun() { |
| if (!compareAndSetState(READY, RUNNING)) |
| return; |
| |
| runner = Thread.currentThread(); |
| if (getState() == RUNNING) { // recheck after setting thread |
| V result; |
| try { |
| result = callable.call(); |
| } catch (Throwable ex) { |
| setException(ex); |
| return; |
| } |
| set(result); |
| } else { |
| releaseShared(0); // cancel |
| } |
| } |
| |
| boolean innerRunAndReset() { |
| if (!compareAndSetState(READY, RUNNING)) |
| return false; |
| try { |
| runner = Thread.currentThread(); |
| if (getState() == RUNNING) |
| callable.call(); // don't set result |
| runner = null; |
| return compareAndSetState(RUNNING, READY); |
| } catch (Throwable ex) { |
| setException(ex); |
| return false; |
| } |
| } |
| } |
| } |