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 NEW.  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:
     * NEW -> NORMAL
     * NEW -> COMPLETING -> NORMAL
     * NEW -> COMPLETING -> EXCEPTIONAL
     * NEW -> CANCELLED
     * NEW -> INTERRUPTING -> INTERRUPTED
     */
    private volatile int state;
    private static final int NEW          = 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 NEW to completed
     */
    private boolean setCompletion(Object x, int mode) {
        // set up transient states
        int next = (x != null) ? COMPLETING : mode;
        if (!UNSAFE.compareAndSwapInt(this, stateOffset, NEW, 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 != NEW;
    }

    public boolean cancel(boolean mayInterruptIfRunning) {
        return state == NEW &&
            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 != NEW ||
            !UNSAFE.compareAndSwapObject(this, runnerOffset,
                                         null, Thread.currentThread()))
            return;

        try {
            // Recheck to avoid missed interrupt.
            if (state != NEW)
                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 != NEW ||
            !UNSAFE.compareAndSwapObject(this, runnerOffset,
                                         null, Thread.currentThread()))
            return false;

        try {
            // Recheck to avoid missed interrupt.
            if (state != NEW)
                return false;
            try {
                callable.call(); // don't set result
                return (state == NEW);
            } 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 = q.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:	1.74
Committed:	Sat Jun 18 01:25:18 2011 UTC (12 years, 11 months ago) by jsr166
Branch:	MAIN
Changes since 1.73:	+1 -1 lines
Log Message:	fix a bug in linked list traversal code
#	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	1.73	* The run state of this task, initially NEW. 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	jsr166	1.73	* NEW -> NORMAL
57			* NEW -> COMPLETING -> NORMAL
58			* NEW -> COMPLETING -> EXCEPTIONAL
59			* NEW -> CANCELLED
60			* NEW -> INTERRUPTING -> INTERRUPTED
61	dl	1.62	*/
62			private volatile int state;
63	jsr166	1.73	private static final int NEW = 0;
64	jsr166	1.70	private static final int COMPLETING = 1;
65			private static final int NORMAL = 2;
66			private static final int EXCEPTIONAL = 3;
67			private static final int CANCELLED = 4;
68			private static final int INTERRUPTING = 5;
69			private static final int INTERRUPTED = 6;
70	dl	1.62
71	jsr166	1.64	/** The underlying callable */
72			private final Callable<V> callable;
73	dl	1.62	/** The result to return or exception to throw from get() */
74			private Object outcome; // non-volatile, protected by state reads/writes
75			/** The thread running the callable; CASed during run() */
76			private volatile Thread runner;
77			/** Treiber stack of waiting threads */
78			private volatile WaitNode waiters;
79
80			/**
81			* Sets completion status, unless already completed. If
82	jsr166	1.69	* necessary, we first set state to transient states COMPLETING
83			* or INTERRUPTING to establish precedence.
84	dl	1.62	*
85			* @param x the outcome
86			* @param mode the completion state value
87	jsr166	1.73	* @return true if this call caused transition from NEW to completed
88	dl	1.62	*/
89			private boolean setCompletion(Object x, int mode) {
90	jsr166	1.69	// set up transient states
91			int next = (x != null) ? COMPLETING : mode;
92	jsr166	1.73	if (!UNSAFE.compareAndSwapInt(this, stateOffset, NEW, next))
93	jsr166	1.68	return false;
94			if (next == INTERRUPTING) {
95	jsr166	1.71	// Must check after CAS to avoid missed interrupt
96			Thread t = runner;
97	jsr166	1.68	if (t != null)
98			t.interrupt();
99	jsr166	1.69	state = INTERRUPTED;
100	jsr166	1.68	}
101			else if (next == COMPLETING) {
102			outcome = x;
103			state = mode;
104	dl	1.62	}
105	jsr166	1.68	if (waiters != null)
106			releaseAll();
107			done();
108			return true;
109	dl	1.62	}
110
111			/**
112	jsr166	1.64	* Returns result or throws exception for completed task.
113			*
114	dl	1.62	* @param s completed state value
115			*/
116			private V report(int s) throws ExecutionException {
117			Object x = outcome;
118			if (s == NORMAL)
119			return (V)x;
120	jsr166	1.69	if (s >= CANCELLED)
121	dl	1.62	throw new CancellationException();
122			throw new ExecutionException((Throwable)x);
123			}
124	dl	1.11
125	tim	1.1	/**
126	jsr166	1.64	* Creates a {@code FutureTask} that will, upon running, execute the
127			* given {@code Callable}.
128	tim	1.1	*
129			* @param callable the callable task
130	dl	1.9	* @throws NullPointerException if callable is null
131	tim	1.1	*/
132			public FutureTask(Callable<V> callable) {
133	dl	1.9	if (callable == null)
134			throw new NullPointerException();
135	dl	1.62	this.callable = callable;
136	tim	1.1	}
137
138			/**
139	jsr166	1.64	* Creates a {@code FutureTask} that will, upon running, execute the
140			* given {@code Runnable}, and arrange that {@code get} will return the
141	tim	1.1	* given result on successful completion.
142			*
143	jsr166	1.54	* @param runnable the runnable task
144	tim	1.1	* @param result the result to return on successful completion. If
145	dl	1.9	* you don't need a particular result, consider using
146	dl	1.16	* constructions of the form:
147	jsr166	1.58	* {@code Future<?> f = new FutureTask<Void>(runnable, null)}
148	dl	1.9	* @throws NullPointerException if runnable is null
149	tim	1.1	*/
150	dl	1.15	public FutureTask(Runnable runnable, V result) {
151	dl	1.62	this.callable = Executors.callable(runnable, result);
152	dl	1.20	}
153
154			public boolean isCancelled() {
155	jsr166	1.69	return state >= CANCELLED;
156	dl	1.20	}
157	jsr166	1.35
158	dl	1.20	public boolean isDone() {
159	jsr166	1.73	return state != NEW;
160	dl	1.13	}
161
162			public boolean cancel(boolean mayInterruptIfRunning) {
163	jsr166	1.73	return state == NEW &&
164	jsr166	1.71	setCompletion(null,
165			mayInterruptIfRunning ? INTERRUPTING : CANCELLED);
166	dl	1.13	}
167	jsr166	1.35
168	jsr166	1.43	/**
169			* @throws CancellationException {@inheritDoc}
170			*/
171	dl	1.2	public V get() throws InterruptedException, ExecutionException {
172	jsr166	1.64	int s = state;
173			if (s <= COMPLETING)
174			s = awaitDone(false, 0L);
175			return report(s);
176	tim	1.1	}
177
178	jsr166	1.43	/**
179			* @throws CancellationException {@inheritDoc}
180			*/
181	dl	1.2	public V get(long timeout, TimeUnit unit)
182	tim	1.1	throws InterruptedException, ExecutionException, TimeoutException {
183	jsr166	1.64	int s = state;
184			if (s <= COMPLETING &&
185			(s = awaitDone(true, unit.toNanos(timeout))) <= COMPLETING)
186	dl	1.62	throw new TimeoutException();
187			return report(s);
188	tim	1.1	}
189
190			/**
191	dl	1.20	* Protected method invoked when this task transitions to state
192	jsr166	1.64	* {@code isDone} (whether normally or via cancellation). The
193	dl	1.20	* default implementation does nothing. Subclasses may override
194			* this method to invoke completion callbacks or perform
195			* bookkeeping. Note that you can query status inside the
196			* implementation of this method to determine whether this task
197			* has been cancelled.
198			*/
199			protected void done() { }
200
201			/**
202	jsr166	1.64	* Sets the result of this future to the given value unless
203	dl	1.29	* this future has already been set or has been cancelled.
204	jsr166	1.64	*
205			* <p>This method is invoked internally by the {@link #run} method
206	dl	1.40	* upon successful completion of the computation.
207	jsr166	1.64	*
208	tim	1.1	* @param v the value
209	jsr166	1.35	*/
210	dl	1.2	protected void set(V v) {
211	dl	1.62	setCompletion(v, NORMAL);
212	tim	1.1	}
213
214			/**
215	jsr166	1.64	* Causes this future to report an {@link ExecutionException}
216			* with the given throwable as its cause, unless this future has
217	dl	1.24	* already been set or has been cancelled.
218	jsr166	1.64	*
219			* <p>This method is invoked internally by the {@link #run} method
220	dl	1.40	* upon failure of the computation.
221	jsr166	1.64	*
222	jsr166	1.41	* @param t the cause of failure
223	jsr166	1.35	*/
224	dl	1.2	protected void setException(Throwable t) {
225	dl	1.62	setCompletion(t, EXCEPTIONAL);
226	tim	1.1	}
227	jsr166	1.35
228	dl	1.24	public void run() {
229	jsr166	1.73	if (state != NEW \|\|
230	jsr166	1.68	!UNSAFE.compareAndSwapObject(this, runnerOffset,
231			null, Thread.currentThread()))
232			return;
233
234			try {
235	jsr166	1.71	// Recheck to avoid missed interrupt.
236	jsr166	1.73	if (state != NEW)
237	jsr166	1.71	return;
238	dl	1.62	V result;
239			try {
240			result = callable.call();
241			} catch (Throwable ex) {
242			setException(ex);
243			return;
244			}
245			set(result);
246	jsr166	1.68	} finally {
247			runner = null;
248	jsr166	1.69	int s = state;
249			if (s >= INTERRUPTING) {
250			while ((s = state) == INTERRUPTING)
251			Thread.yield(); // wait out pending cancellation interrupt
252			Thread.interrupted(); // clear any interrupt from cancel(true)
253			}
254	dl	1.62	}
255	dl	1.24	}
256
257			/**
258	dl	1.30	* Executes the computation without setting its result, and then
259	jsr166	1.64	* resets this future to initial state, failing to do so if the
260	dl	1.24	* computation encounters an exception or is cancelled. This is
261			* designed for use with tasks that intrinsically execute more
262			* than once.
263	jsr166	1.64	*
264	dl	1.24	* @return true if successfully run and reset
265			*/
266			protected boolean runAndReset() {
267	jsr166	1.73	if (state != NEW \|\|
268	jsr166	1.66	!UNSAFE.compareAndSwapObject(this, runnerOffset,
269			null, Thread.currentThread()))
270	dl	1.62	return false;
271	jsr166	1.68
272	dl	1.62	try {
273	jsr166	1.71	// Recheck to avoid missed interrupt.
274	jsr166	1.73	if (state != NEW)
275	jsr166	1.71	return false;
276	jsr166	1.68	try {
277			callable.call(); // don't set result
278	jsr166	1.73	return (state == NEW);
279	jsr166	1.68	} catch (Throwable ex) {
280			setException(ex);
281	dl	1.62	return false;
282	jsr166	1.68	}
283			} finally {
284			runner = null;
285	jsr166	1.69	int s = state;
286			if (s >= INTERRUPTING) {
287			while ((s = state) == INTERRUPTING)
288			Thread.yield(); // wait out pending cancellation interrupt
289			Thread.interrupted(); // clear any interrupt from cancel(true)
290			}
291	dl	1.62	}
292	dl	1.14	}
293	dl	1.3
294	dl	1.14	/**
295	dl	1.62	* Simple linked list nodes to record waiting threads in a Treiber
296	jsr166	1.64	* stack. See other classes such as Phaser and SynchronousQueue
297	dl	1.62	* for more detailed explanation.
298	dl	1.20	*/
299	dl	1.62	static final class WaitNode {
300			volatile Thread thread;
301			WaitNode next;
302			}
303	dl	1.42
304	dl	1.62	/**
305	jsr166	1.64	* Removes and signals all waiting threads.
306	dl	1.62	*/
307			private void releaseAll() {
308			WaitNode q;
309			while ((q = waiters) != null) {
310			if (UNSAFE.compareAndSwapObject(this, waitersOffset, q, null)) {
311			for (;;) {
312			Thread t = q.thread;
313			if (t != null) {
314			q.thread = null;
315			LockSupport.unpark(t);
316			}
317			WaitNode next = q.next;
318			if (next == null)
319			return;
320			q.next = null; // unlink to help gc
321			q = next;
322			}
323			}
324	dl	1.24	}
325	dl	1.62	}
326	dl	1.24
327	dl	1.62	/**
328	jsr166	1.64	* Awaits completion or aborts on interrupt or timeout.
329			*
330	dl	1.62	* @param timed true if use timed waits
331	jsr166	1.64	* @param nanos time to wait, if timed
332	dl	1.62	* @return state upon completion
333			*/
334			private int awaitDone(boolean timed, long nanos)
335			throws InterruptedException {
336	jsr166	1.63	long last = timed ? System.nanoTime() : 0L;
337	dl	1.62	WaitNode q = null;
338			boolean queued = false;
339	jsr166	1.64	for (;;) {
340	dl	1.62	if (Thread.interrupted()) {
341			removeWaiter(q);
342			throw new InterruptedException();
343			}
344	jsr166	1.64
345			int s = state;
346			if (s > COMPLETING) {
347	dl	1.62	if (q != null)
348			q.thread = null;
349			return s;
350			}
351			else if (q == null)
352			q = new WaitNode();
353			else if (!queued)
354			queued = UNSAFE.compareAndSwapObject(this, waitersOffset,
355			q.next = waiters, q);
356			else if (q.thread == null)
357			q.thread = Thread.currentThread();
358			else if (timed) {
359			long now = System.nanoTime();
360			if ((nanos -= (now - last)) <= 0L) {
361			removeWaiter(q);
362			return state;
363	dl	1.50	}
364	dl	1.62	last = now;
365			LockSupport.parkNanos(this, nanos);
366	dl	1.50	}
367	dl	1.62	else
368			LockSupport.park(this);
369	dl	1.24	}
370	dl	1.62	}
371	dl	1.24
372	dl	1.62	/**
373	jsr166	1.64	* Tries to unlink a timed-out or interrupted wait node to avoid
374			* accumulating garbage. Internal nodes are simply unspliced
375	dl	1.62	* without CAS since it is harmless if they are traversed anyway
376			* by releasers or concurrent calls to removeWaiter.
377			*/
378			private void removeWaiter(WaitNode node) {
379			if (node != null) {
380			node.thread = null;
381			WaitNode pred = null;
382			WaitNode q = waiters;
383			while (q != null) {
384	jsr166	1.74	WaitNode next = q.next;
385	dl	1.62	if (q != node) {
386			pred = q;
387			q = next;
388	dl	1.50	}
389	dl	1.62	else if (pred != null) {
390			pred.next = next;
391			break;
392	dl	1.50	}
393	dl	1.62	else if (UNSAFE.compareAndSwapObject(this, waitersOffset,
394			q, next))
395	jsr166	1.56	break;
396	dl	1.62	else { // restart on CAS failure
397			pred = null;
398			q = waiters;
399	jsr166	1.55	}
400	jsr166	1.56	}
401	dl	1.14	}
402	dl	1.62	}
403	dl	1.14
404	dl	1.62	// Unsafe mechanics
405			private static final sun.misc.Unsafe UNSAFE;
406			private static final long stateOffset;
407			private static final long runnerOffset;
408			private static final long waitersOffset;
409			static {
410			try {
411			UNSAFE = sun.misc.Unsafe.getUnsafe();
412			Class<?> k = FutureTask.class;
413			stateOffset = UNSAFE.objectFieldOffset
414			(k.getDeclaredField("state"));
415			runnerOffset = UNSAFE.objectFieldOffset
416			(k.getDeclaredField("runner"));
417			waitersOffset = UNSAFE.objectFieldOffset
418			(k.getDeclaredField("waiters"));
419			} catch (Exception e) {
420			throw new Error(e);
421	dl	1.14	}
422	dl	1.15	}
423	dl	1.62
424	dl	1.15	}