util/concurrent/FutureTask.java

/*
 * 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/publicdomain/zero/1.0/
 */

package java.util.concurrent;
import java.util.concurrent.locks.LockSupport;

/**
 * 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 {@code get}
 * methods will block if the computation has not yet completed.  Once
 * the computation has completed, the computation cannot be restarted
 * or cancelled (unless the computation is invoked using
 * {@link #runAndReset}).
 *
 * <p>A {@code FutureTask} can be used to wrap a {@link Callable} or
 * {@link Runnable} object.  Because {@code FutureTask} implements
 * {@code Runnable}, a {@code FutureTask} can be submitted to an
 * {@link Executor} for execution.
 *
 * <p>In addition to serving as a standalone class, this class provides
 * {@code protected} 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 {@code get} methods
 */
public class FutureTask<V> implements RunnableFuture<V> {
    /*
     * Revision notes: This differs from previous versions of this
     * class that relied on AbstractQueuedSynchronizer, mainly to
     * avoid surprising users about retaining interrupt status during
     * cancellation races. Sync control in the current design relies
     * on a "state" field updated via CAS to track completion, along
     * with a simple Treiber stack to hold waiting threads.
     *
     * Style note: As usual, we bypass overhead of using
     * AtomicXFieldUpdaters and instead directly use Unsafe intrinsics.
     */

    /**
     * The run state of this task, initially UNDECIDED.  The run state
     * transitions to a terminal state only in method setCompletion.
     * During setCompletion, state may take on transient values of
     * COMPLETING (while outcome is being set) or INTERRUPTING (only
     * while interrupting the runner to satisfy a cancel(true)).
     * State values are highly order-dependent to simplify checks.
     *
     * Possible state transitions:
     * UNDECIDED -> COMPLETING -> NORMAL
     * UNDECIDED -> COMPLETING -> EXCEPTIONAL
     * UNDECIDED -> CANCELLED
     * UNDECIDED -> INTERRUPTING -> INTERRUPTED
     */
    private volatile int state;
    private static final int UNDECIDED    = 0;
    private static final int COMPLETING   = 1;
    private static final int NORMAL       = 2;
    private static final int EXCEPTIONAL  = 3;
    private static final int CANCELLED    = 4;
    private static final int INTERRUPTING = 5;
    private static final int INTERRUPTED  = 6;

    /** The underlying callable */
    private final Callable<V> callable;
    /** The result to return or exception to throw from get() */
    private Object outcome; // non-volatile, protected by state reads/writes
    /** The thread running the callable; CASed during run() */
    private volatile Thread runner;
    /** Treiber stack of waiting threads */
    private volatile WaitNode waiters;

    /**
     * Sets completion status, unless already completed.  If
     * necessary, we first set state to transient states COMPLETING
     * or INTERRUPTING to establish precedence.
     *
     * @param x the outcome
     * @param mode the completion state value
     * @return true if this call caused transition from UNDECIDED to completed
     */
    private boolean setCompletion(Object x, int mode) {
        // set up transient states
        int next = (x != null) ? COMPLETING : mode;
        if (!UNSAFE.compareAndSwapInt(this, stateOffset, UNDECIDED, next))
            return false;
        if (next == INTERRUPTING) {
            // Must check after CAS to avoid missed interrupt
            Thread t = runner;
            if (t != null)
                t.interrupt();
            state = INTERRUPTED;
        }
        else if (next == COMPLETING) {
            outcome = x;
            state = mode;
        }
        if (waiters != null)
            releaseAll();
        done();
        return true;
    }

    /**
     * Returns result or throws exception for completed task.
     *
     * @param s completed state value
     */
    private V report(int s) throws ExecutionException {
        Object x = outcome;
        if (s == NORMAL)
            return (V)x;
        if (s >= CANCELLED)
            throw new CancellationException();
        throw new ExecutionException((Throwable)x);
    }

    /**
     * Creates a {@code FutureTask} that will, upon running, execute the
     * given {@code Callable}.
     *
     * @param  callable the callable task
     * @throws NullPointerException if callable is null
     */
    public FutureTask(Callable<V> callable) {
        if (callable == null)
            throw new NullPointerException();
        this.callable = callable;
    }

    /**
     * Creates a {@code FutureTask} that will, upon running, execute the
     * given {@code Runnable}, and arrange that {@code get} 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:
     * {@code Future<?> f = new FutureTask<Void>(runnable, null)}
     * @throws NullPointerException if runnable is null
     */
    public FutureTask(Runnable runnable, V result) {
        this.callable = Executors.callable(runnable, result);
    }

    public boolean isCancelled() {
        return state >= CANCELLED;
    }

    public boolean isDone() {
        return state != UNDECIDED;
    }

    public boolean cancel(boolean mayInterruptIfRunning) {
        return state == UNDECIDED &&
            setCompletion(null,
                          mayInterruptIfRunning ? INTERRUPTING : CANCELLED);
    }

    /**
     * @throws CancellationException {@inheritDoc}
     */
    public V get() throws InterruptedException, ExecutionException {
        int s = state;
        if (s <= COMPLETING)
            s = awaitDone(false, 0L);
        return report(s);
    }

    /**
     * @throws CancellationException {@inheritDoc}
     */
    public V get(long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException {
        int s = state;
        if (s <= COMPLETING &&
            (s = awaitDone(true, unit.toNanos(timeout))) <= COMPLETING)
            throw new TimeoutException();
        return report(s);
    }

    /**
     * Protected method invoked when this task transitions to state
     * {@code isDone} (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.
     *
     * <p>This method is invoked internally by the {@link #run} method
     * upon successful completion of the computation.
     *
     * @param v the value
     */
    protected void set(V v) {
        setCompletion(v, NORMAL);
    }

    /**
     * Causes this future to report an {@link ExecutionException}
     * with the given throwable as its cause, unless this future has
     * already been set or has been cancelled.
     *
     * <p>This method is invoked internally by the {@link #run} method
     * upon failure of the computation.
     *
     * @param t the cause of failure
     */
    protected void setException(Throwable t) {
        setCompletion(t, EXCEPTIONAL);
    }

    public void run() {
        if (state != UNDECIDED ||
            !UNSAFE.compareAndSwapObject(this, runnerOffset,
                                         null, Thread.currentThread()))
            return;

        try {
            // Recheck to avoid missed interrupt.
            if (state != UNDECIDED)
                return;
            V result;
            try {
                result = callable.call();
            } catch (Throwable ex) {
                setException(ex);
                return;
            }
            set(result);
        } finally {
            runner = null;
            int s = state;
            if (s >= INTERRUPTING) {
                while ((s = state) == INTERRUPTING)
                    Thread.yield(); // wait out pending cancellation interrupt
                Thread.interrupted(); // clear any interrupt from cancel(true)
            }
        }
    }

    /**
     * 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() {
        if (state != UNDECIDED ||
            !UNSAFE.compareAndSwapObject(this, runnerOffset,
                                         null, Thread.currentThread()))
            return false;

        try {
            // Recheck to avoid missed interrupt.
            if (state != UNDECIDED)
                return false;
            try {
                callable.call(); // don't set result
                return (state == UNDECIDED);
            } catch (Throwable ex) {
                setException(ex);
                return false;
            }
        } finally {
            runner = null;
            int s = state;
            if (s >= INTERRUPTING) {
                while ((s = state) == INTERRUPTING)
                    Thread.yield(); // wait out pending cancellation interrupt
                Thread.interrupted(); // clear any interrupt from cancel(true)
            }
        }
    }

    /**
     * Simple linked list nodes to record waiting threads in a Treiber
     * stack.  See other classes such as Phaser and SynchronousQueue
     * for more detailed explanation.
     */
    static final class WaitNode {
        volatile Thread thread;
        WaitNode next;
    }

    /**
     * Removes and signals all waiting threads.
     */
    private void releaseAll() {
        WaitNode q;
        while ((q = waiters) != null) {
            if (UNSAFE.compareAndSwapObject(this, waitersOffset, q, null)) {
                for (;;) {
                    Thread t = q.thread;
                    if (t != null) {
                        q.thread = null;
                        LockSupport.unpark(t);
                    }
                    WaitNode next = q.next;
                    if (next == null)
                        return;
                    q.next = null; // unlink to help gc
                    q = next;
                }
            }
        }
    }

    /**
     * Awaits completion or aborts on interrupt or timeout.
     *
     * @param timed true if use timed waits
     * @param nanos time to wait, if timed
     * @return state upon completion
     */
    private int awaitDone(boolean timed, long nanos)
        throws InterruptedException {
        long last = timed ? System.nanoTime() : 0L;
        WaitNode q = null;
        boolean queued = false;
        for (;;) {
            if (Thread.interrupted()) {
                removeWaiter(q);
                throw new InterruptedException();
            }

            int s = state;
            if (s > COMPLETING) {
                if (q != null)
                    q.thread = null;
                return s;
            }
            else if (q == null)
                q = new WaitNode();
            else if (!queued)
                queued = UNSAFE.compareAndSwapObject(this, waitersOffset,
                                                     q.next = waiters, q);
            else if (q.thread == null)
                q.thread = Thread.currentThread();
            else if (timed) {
                long now = System.nanoTime();
                if ((nanos -= (now - last)) <= 0L) {
                    removeWaiter(q);
                    return state;
                }
                last = now;
                LockSupport.parkNanos(this, nanos);
            }
            else
                LockSupport.park(this);
        }
    }

    /**
     * Tries to unlink a timed-out or interrupted wait node to avoid
     * accumulating garbage.  Internal nodes are simply unspliced
     * without CAS since it is harmless if they are traversed anyway
     * by releasers or concurrent calls to removeWaiter.
     */
    private void removeWaiter(WaitNode node) {
        if (node != null) {
            node.thread = null;
            WaitNode pred = null;
            WaitNode q = waiters;
            while (q != null) {
                WaitNode next = node.next;
                if (q != node) {
                    pred = q;
                    q = next;
                }
                else if (pred != null) {
                    pred.next = next;
                    break;
                }
                else if (UNSAFE.compareAndSwapObject(this, waitersOffset,
                                                     q, next))
                    break;
                else { // restart on CAS failure
                    pred = null;
                    q = waiters;
                }
            }
        }
    }

    // Unsafe mechanics
    private static final sun.misc.Unsafe UNSAFE;
    private static final long stateOffset;
    private static final long runnerOffset;
    private static final long waitersOffset;
    static {
        try {
            UNSAFE = sun.misc.Unsafe.getUnsafe();
            Class<?> k = FutureTask.class;
            stateOffset = UNSAFE.objectFieldOffset
                (k.getDeclaredField("state"));
            runnerOffset = UNSAFE.objectFieldOffset
                (k.getDeclaredField("runner"));
            waitersOffset = UNSAFE.objectFieldOffset
                (k.getDeclaredField("waiters"));
        } catch (Exception e) {
            throw new Error(e);
        }
    }

}
Revision:	1.71
Committed:	Fri Jun 17 23:29:40 2011 UTC (12 years, 11 months ago) by jsr166
Branch:	MAIN
Changes since 1.70:	+10 -3 lines
Log Message:	fix race causing interrupt to not be delivered
#	User	Rev	Content
1	tim	1.1	/*
2	dl	1.2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	dl	1.23	* Expert Group and released to the public domain, as explained at
4	jsr166	1.59	* http://creativecommons.org/publicdomain/zero/1.0/
5	tim	1.1	*/
6
7			package java.util.concurrent;
8	dl	1.62	import java.util.concurrent.locks.LockSupport;
9	dl	1.13
10	tim	1.1	/**
11	dl	1.8	* A cancellable asynchronous computation. This class provides a base
12			* implementation of {@link Future}, with methods to start and cancel
13			* a computation, query to see if the computation is complete, and
14	dl	1.4	* retrieve the result of the computation. The result can only be
15	jsr166	1.64	* retrieved when the computation has completed; the {@code get}
16			* methods will block if the computation has not yet completed. Once
17	dl	1.8	* the computation has completed, the computation cannot be restarted
18	jsr166	1.64	* or cancelled (unless the computation is invoked using
19			* {@link #runAndReset}).
20	tim	1.1	*
21	jsr166	1.64	* <p>A {@code FutureTask} can be used to wrap a {@link Callable} or
22			* {@link Runnable} object. Because {@code FutureTask} implements
23			* {@code Runnable}, a {@code FutureTask} can be submitted to an
24			* {@link Executor} for execution.
25	tim	1.1	*
26	dl	1.14	* <p>In addition to serving as a standalone class, this class provides
27	jsr166	1.64	* {@code protected} functionality that may be useful when creating
28	dl	1.14	* customized task classes.
29			*
30	tim	1.1	* @since 1.5
31	dl	1.4	* @author Doug Lea
32	jsr166	1.64	* @param <V> The result type returned by this FutureTask's {@code get} methods
33	tim	1.1	*/
34	peierls	1.39	public class FutureTask<V> implements RunnableFuture<V> {
35	dl	1.62	/*
36			* Revision notes: This differs from previous versions of this
37			* class that relied on AbstractQueuedSynchronizer, mainly to
38			* avoid surprising users about retaining interrupt status during
39			* cancellation races. Sync control in the current design relies
40			* on a "state" field updated via CAS to track completion, along
41			* with a simple Treiber stack to hold waiting threads.
42			*
43			* Style note: As usual, we bypass overhead of using
44			* AtomicXFieldUpdaters and instead directly use Unsafe intrinsics.
45			*/
46
47			/**
48	jsr166	1.67	* The run state of this task, initially UNDECIDED. The run state
49	jsr166	1.69	* transitions to a terminal state only in method setCompletion.
50			* During setCompletion, state may take on transient values of
51			* COMPLETING (while outcome is being set) or INTERRUPTING (only
52			* while interrupting the runner to satisfy a cancel(true)).
53	jsr166	1.70	* State values are highly order-dependent to simplify checks.
54	jsr166	1.69	*
55			* Possible state transitions:
56			* UNDECIDED -> COMPLETING -> NORMAL
57			* UNDECIDED -> COMPLETING -> EXCEPTIONAL
58			* UNDECIDED -> CANCELLED
59			* UNDECIDED -> INTERRUPTING -> INTERRUPTED
60	dl	1.62	*/
61			private volatile int state;
62	jsr166	1.70	private static final int UNDECIDED = 0;
63			private static final int COMPLETING = 1;
64			private static final int NORMAL = 2;
65			private static final int EXCEPTIONAL = 3;
66			private static final int CANCELLED = 4;
67			private static final int INTERRUPTING = 5;
68			private static final int INTERRUPTED = 6;
69	dl	1.62
70	jsr166	1.64	/** The underlying callable */
71			private final Callable<V> callable;
72	dl	1.62	/** The result to return or exception to throw from get() */
73			private Object outcome; // non-volatile, protected by state reads/writes
74			/** The thread running the callable; CASed during run() */
75			private volatile Thread runner;
76			/** Treiber stack of waiting threads */
77			private volatile WaitNode waiters;
78
79			/**
80			* Sets completion status, unless already completed. If
81	jsr166	1.69	* necessary, we first set state to transient states COMPLETING
82			* or INTERRUPTING to establish precedence.
83	dl	1.62	*
84			* @param x the outcome
85			* @param mode the completion state value
86	jsr166	1.67	* @return true if this call caused transition from UNDECIDED to completed
87	dl	1.62	*/
88			private boolean setCompletion(Object x, int mode) {
89	jsr166	1.69	// set up transient states
90			int next = (x != null) ? COMPLETING : mode;
91			if (!UNSAFE.compareAndSwapInt(this, stateOffset, UNDECIDED, next))
92	jsr166	1.68	return false;
93			if (next == INTERRUPTING) {
94	jsr166	1.71	// Must check after CAS to avoid missed interrupt
95			Thread t = runner;
96	jsr166	1.68	if (t != null)
97			t.interrupt();
98	jsr166	1.69	state = INTERRUPTED;
99	jsr166	1.68	}
100			else if (next == COMPLETING) {
101			outcome = x;
102			state = mode;
103	dl	1.62	}
104	jsr166	1.68	if (waiters != null)
105			releaseAll();
106			done();
107			return true;
108	dl	1.62	}
109
110			/**
111	jsr166	1.64	* Returns result or throws exception for completed task.
112			*
113	dl	1.62	* @param s completed state value
114			*/
115			private V report(int s) throws ExecutionException {
116			Object x = outcome;
117			if (s == NORMAL)
118			return (V)x;
119	jsr166	1.69	if (s >= CANCELLED)
120	dl	1.62	throw new CancellationException();
121			throw new ExecutionException((Throwable)x);
122			}
123	dl	1.11
124	tim	1.1	/**
125	jsr166	1.64	* Creates a {@code FutureTask} that will, upon running, execute the
126			* given {@code Callable}.
127	tim	1.1	*
128			* @param callable the callable task
129	dl	1.9	* @throws NullPointerException if callable is null
130	tim	1.1	*/
131			public FutureTask(Callable<V> callable) {
132	dl	1.9	if (callable == null)
133			throw new NullPointerException();
134	dl	1.62	this.callable = callable;
135	tim	1.1	}
136
137			/**
138	jsr166	1.64	* Creates a {@code FutureTask} that will, upon running, execute the
139			* given {@code Runnable}, and arrange that {@code get} will return the
140	tim	1.1	* given result on successful completion.
141			*
142	jsr166	1.54	* @param runnable the runnable task
143	tim	1.1	* @param result the result to return on successful completion. If
144	dl	1.9	* you don't need a particular result, consider using
145	dl	1.16	* constructions of the form:
146	jsr166	1.58	* {@code Future<?> f = new FutureTask<Void>(runnable, null)}
147	dl	1.9	* @throws NullPointerException if runnable is null
148	tim	1.1	*/
149	dl	1.15	public FutureTask(Runnable runnable, V result) {
150	dl	1.62	this.callable = Executors.callable(runnable, result);
151	dl	1.20	}
152
153			public boolean isCancelled() {
154	jsr166	1.69	return state >= CANCELLED;
155	dl	1.20	}
156	jsr166	1.35
157	dl	1.20	public boolean isDone() {
158	jsr166	1.67	return state != UNDECIDED;
159	dl	1.13	}
160
161			public boolean cancel(boolean mayInterruptIfRunning) {
162	jsr166	1.67	return state == UNDECIDED &&
163	jsr166	1.71	setCompletion(null,
164			mayInterruptIfRunning ? INTERRUPTING : CANCELLED);
165	dl	1.13	}
166	jsr166	1.35
167	jsr166	1.43	/**
168			* @throws CancellationException {@inheritDoc}
169			*/
170	dl	1.2	public V get() throws InterruptedException, ExecutionException {
171	jsr166	1.64	int s = state;
172			if (s <= COMPLETING)
173			s = awaitDone(false, 0L);
174			return report(s);
175	tim	1.1	}
176
177	jsr166	1.43	/**
178			* @throws CancellationException {@inheritDoc}
179			*/
180	dl	1.2	public V get(long timeout, TimeUnit unit)
181	tim	1.1	throws InterruptedException, ExecutionException, TimeoutException {
182	jsr166	1.64	int s = state;
183			if (s <= COMPLETING &&
184			(s = awaitDone(true, unit.toNanos(timeout))) <= COMPLETING)
185	dl	1.62	throw new TimeoutException();
186			return report(s);
187	tim	1.1	}
188
189			/**
190	dl	1.20	* Protected method invoked when this task transitions to state
191	jsr166	1.64	* {@code isDone} (whether normally or via cancellation). The
192	dl	1.20	* default implementation does nothing. Subclasses may override
193			* this method to invoke completion callbacks or perform
194			* bookkeeping. Note that you can query status inside the
195			* implementation of this method to determine whether this task
196			* has been cancelled.
197			*/
198			protected void done() { }
199
200			/**
201	jsr166	1.64	* Sets the result of this future to the given value unless
202	dl	1.29	* this future has already been set or has been cancelled.
203	jsr166	1.64	*
204			* <p>This method is invoked internally by the {@link #run} method
205	dl	1.40	* upon successful completion of the computation.
206	jsr166	1.64	*
207	tim	1.1	* @param v the value
208	jsr166	1.35	*/
209	dl	1.2	protected void set(V v) {
210	dl	1.62	setCompletion(v, NORMAL);
211	tim	1.1	}
212
213			/**
214	jsr166	1.64	* Causes this future to report an {@link ExecutionException}
215			* with the given throwable as its cause, unless this future has
216	dl	1.24	* already been set or has been cancelled.
217	jsr166	1.64	*
218			* <p>This method is invoked internally by the {@link #run} method
219	dl	1.40	* upon failure of the computation.
220	jsr166	1.64	*
221	jsr166	1.41	* @param t the cause of failure
222	jsr166	1.35	*/
223	dl	1.2	protected void setException(Throwable t) {
224	dl	1.62	setCompletion(t, EXCEPTIONAL);
225	tim	1.1	}
226	jsr166	1.35
227	dl	1.24	public void run() {
228	jsr166	1.68	if (state != UNDECIDED \|\|
229			!UNSAFE.compareAndSwapObject(this, runnerOffset,
230			null, Thread.currentThread()))
231			return;
232
233			try {
234	jsr166	1.71	// Recheck to avoid missed interrupt.
235			if (state != UNDECIDED)
236			return;
237	dl	1.62	V result;
238			try {
239			result = callable.call();
240			} catch (Throwable ex) {
241			setException(ex);
242			return;
243			}
244			set(result);
245	jsr166	1.68	} finally {
246			runner = null;
247	jsr166	1.69	int s = state;
248			if (s >= INTERRUPTING) {
249			while ((s = state) == INTERRUPTING)
250			Thread.yield(); // wait out pending cancellation interrupt
251			Thread.interrupted(); // clear any interrupt from cancel(true)
252			}
253	dl	1.62	}
254	dl	1.24	}
255
256			/**
257	dl	1.30	* Executes the computation without setting its result, and then
258	jsr166	1.64	* resets this future to initial state, failing to do so if the
259	dl	1.24	* computation encounters an exception or is cancelled. This is
260			* designed for use with tasks that intrinsically execute more
261			* than once.
262	jsr166	1.64	*
263	dl	1.24	* @return true if successfully run and reset
264			*/
265			protected boolean runAndReset() {
266	jsr166	1.67	if (state != UNDECIDED \|\|
267	jsr166	1.66	!UNSAFE.compareAndSwapObject(this, runnerOffset,
268			null, Thread.currentThread()))
269	dl	1.62	return false;
270	jsr166	1.68
271	dl	1.62	try {
272	jsr166	1.71	// Recheck to avoid missed interrupt.
273			if (state != UNDECIDED)
274			return false;
275	jsr166	1.68	try {
276			callable.call(); // don't set result
277			return (state == UNDECIDED);
278			} catch (Throwable ex) {
279			setException(ex);
280	dl	1.62	return false;
281	jsr166	1.68	}
282			} finally {
283			runner = null;
284	jsr166	1.69	int s = state;
285			if (s >= INTERRUPTING) {
286			while ((s = state) == INTERRUPTING)
287			Thread.yield(); // wait out pending cancellation interrupt
288			Thread.interrupted(); // clear any interrupt from cancel(true)
289			}
290	dl	1.62	}
291	dl	1.14	}
292	dl	1.3
293	dl	1.14	/**
294	dl	1.62	* Simple linked list nodes to record waiting threads in a Treiber
295	jsr166	1.64	* stack. See other classes such as Phaser and SynchronousQueue
296	dl	1.62	* for more detailed explanation.
297	dl	1.20	*/
298	dl	1.62	static final class WaitNode {
299			volatile Thread thread;
300			WaitNode next;
301			}
302	dl	1.42
303	dl	1.62	/**
304	jsr166	1.64	* Removes and signals all waiting threads.
305	dl	1.62	*/
306			private void releaseAll() {
307			WaitNode q;
308			while ((q = waiters) != null) {
309			if (UNSAFE.compareAndSwapObject(this, waitersOffset, q, null)) {
310			for (;;) {
311			Thread t = q.thread;
312			if (t != null) {
313			q.thread = null;
314			LockSupport.unpark(t);
315			}
316			WaitNode next = q.next;
317			if (next == null)
318			return;
319			q.next = null; // unlink to help gc
320			q = next;
321			}
322			}
323	dl	1.24	}
324	dl	1.62	}
325	dl	1.24
326	dl	1.62	/**
327	jsr166	1.64	* Awaits completion or aborts on interrupt or timeout.
328			*
329	dl	1.62	* @param timed true if use timed waits
330	jsr166	1.64	* @param nanos time to wait, if timed
331	dl	1.62	* @return state upon completion
332			*/
333			private int awaitDone(boolean timed, long nanos)
334			throws InterruptedException {
335	jsr166	1.63	long last = timed ? System.nanoTime() : 0L;
336	dl	1.62	WaitNode q = null;
337			boolean queued = false;
338	jsr166	1.64	for (;;) {
339	dl	1.62	if (Thread.interrupted()) {
340			removeWaiter(q);
341			throw new InterruptedException();
342			}
343	jsr166	1.64
344			int s = state;
345			if (s > COMPLETING) {
346	dl	1.62	if (q != null)
347			q.thread = null;
348			return s;
349			}
350			else if (q == null)
351			q = new WaitNode();
352			else if (!queued)
353			queued = UNSAFE.compareAndSwapObject(this, waitersOffset,
354			q.next = waiters, q);
355			else if (q.thread == null)
356			q.thread = Thread.currentThread();
357			else if (timed) {
358			long now = System.nanoTime();
359			if ((nanos -= (now - last)) <= 0L) {
360			removeWaiter(q);
361			return state;
362	dl	1.50	}
363	dl	1.62	last = now;
364			LockSupport.parkNanos(this, nanos);
365	dl	1.50	}
366	dl	1.62	else
367			LockSupport.park(this);
368	dl	1.24	}
369	dl	1.62	}
370	dl	1.24
371	dl	1.62	/**
372	jsr166	1.64	* Tries to unlink a timed-out or interrupted wait node to avoid
373			* accumulating garbage. Internal nodes are simply unspliced
374	dl	1.62	* without CAS since it is harmless if they are traversed anyway
375			* by releasers or concurrent calls to removeWaiter.
376			*/
377			private void removeWaiter(WaitNode node) {
378			if (node != null) {
379			node.thread = null;
380			WaitNode pred = null;
381			WaitNode q = waiters;
382			while (q != null) {
383			WaitNode next = node.next;
384			if (q != node) {
385			pred = q;
386			q = next;
387	dl	1.50	}
388	dl	1.62	else if (pred != null) {
389			pred.next = next;
390			break;
391	dl	1.50	}
392	dl	1.62	else if (UNSAFE.compareAndSwapObject(this, waitersOffset,
393			q, next))
394	jsr166	1.56	break;
395	dl	1.62	else { // restart on CAS failure
396			pred = null;
397			q = waiters;
398	jsr166	1.55	}
399	jsr166	1.56	}
400	dl	1.14	}
401	dl	1.62	}
402	dl	1.14
403	dl	1.62	// Unsafe mechanics
404			private static final sun.misc.Unsafe UNSAFE;
405			private static final long stateOffset;
406			private static final long runnerOffset;
407			private static final long waitersOffset;
408			static {
409			try {
410			UNSAFE = sun.misc.Unsafe.getUnsafe();
411			Class<?> k = FutureTask.class;
412			stateOffset = UNSAFE.objectFieldOffset
413			(k.getDeclaredField("state"));
414			runnerOffset = UNSAFE.objectFieldOffset
415			(k.getDeclaredField("runner"));
416			waitersOffset = UNSAFE.objectFieldOffset
417			(k.getDeclaredField("waiters"));
418			} catch (Exception e) {
419			throw new Error(e);
420	dl	1.14	}
421	dl	1.15	}
422	dl	1.62
423	dl	1.15	}