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 NORMAL, EXCEPTIONAL, or CANCELLED (only) in
     * method setCompletion.  During setCompletion, state may take on
     * transient values of COMPLETING (while outcome is being set) or
     * INTERRUPTING (while interrupting the runner).  State values are
     * ordered and set to powers of two to simplify checks.
     */
    private volatile int state;
    private static final int UNDECIDED    = 0x00;
    private static final int COMPLETING   = 0x01;
    private static final int INTERRUPTING = 0x02;
    private static final int NORMAL       = 0x04;
    private static final int EXCEPTIONAL  = 0x08;
    private static final int CANCELLED    = 0x10;

    /** 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 COMPLETING or INTERRUPTING to
     * establish precedence.  This intentionally stalls (just via
     * yields) in (uncommon) cases of concurrent calls during
     * cancellation until state is set, to avoid surprising users
     * during cancellation races.
     *
     * @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) {
        Thread r = runner;
        if (r == Thread.currentThread()) // null out runner on completion
            UNSAFE.putObject(this, runnerOffset, r = null); // nonvolatile OK
        int next = ((mode == INTERRUPTING) ? // set up transient states
                    (r != null) ? INTERRUPTING : CANCELLED :
                    (x != null) ? COMPLETING : mode);
        for (;;) {
            int s = state;
            if (s == UNDECIDED) {
                if (UNSAFE.compareAndSwapInt(this, stateOffset,
                                             UNDECIDED, next)) {
                    if (next == INTERRUPTING) {
                        Thread t = runner; // recheck
                        if (t != null)
                            t.interrupt();
                        state = CANCELLED;
                    }
                    else if (next == COMPLETING) {
                        outcome = x;
                        state = mode;
                    }
                    if (waiters != null)
                        releaseAll();
                    done();
                    return true;
                }
            }
            else if (s == INTERRUPTING)
                Thread.yield(); // wait out pending cancellation interrupt
            else
                return false;
        }
    }

    /**
     * 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 | INTERRUPTING)) != 0)
            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 | INTERRUPTING)) != 0;
    }

    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())) {
            V result;
            try {
                result = callable.call();
            } catch (Throwable ex) {
                setException(ex);
                return;
            }
            set(result);
        }
    }

    /**
     * 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 {
            callable.call(); // don't set result
        } catch (Throwable ex) {
            setException(ex);
            return false;
        }
        runner = null;
        for (;;) {
            int s = state;
            if (s == UNDECIDED)
                return true;
            if (s != INTERRUPTING)
                return false;
            Thread.yield(); // wait out pending cancellation interrupt
        }
    }

    /**
     * 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:	1.67
Committed:	Fri Jun 17 21:07:12 2011 UTC (12 years, 11 months ago) by jsr166
Branch:	MAIN
Changes since 1.66:	+14 -12 lines
Log Message:	reintroduce a constant, UNDECIDED, for state 0
#	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	dl	1.62	* transitions to NORMAL, EXCEPTIONAL, or CANCELLED (only) in
50	jsr166	1.67	* method setCompletion. During setCompletion, state may take on
51	dl	1.62	* transient values of COMPLETING (while outcome is being set) or
52	jsr166	1.67	* INTERRUPTING (while interrupting the runner). State values are
53			* ordered and set to powers of two to simplify checks.
54	dl	1.62	*/
55			private volatile int state;
56	jsr166	1.67	private static final int UNDECIDED = 0x00;
57	dl	1.62	private static final int COMPLETING = 0x01;
58			private static final int INTERRUPTING = 0x02;
59			private static final int NORMAL = 0x04;
60			private static final int EXCEPTIONAL = 0x08;
61			private static final int CANCELLED = 0x10;
62
63	jsr166	1.64	/** The underlying callable */
64			private final Callable<V> callable;
65	dl	1.62	/** The result to return or exception to throw from get() */
66			private Object outcome; // non-volatile, protected by state reads/writes
67			/** The thread running the callable; CASed during run() */
68			private volatile Thread runner;
69			/** Treiber stack of waiting threads */
70			private volatile WaitNode waiters;
71
72			/**
73			* Sets completion status, unless already completed. If
74			* necessary, we first set state to COMPLETING or INTERRUPTING to
75	jsr166	1.64	* establish precedence. This intentionally stalls (just via
76	dl	1.62	* yields) in (uncommon) cases of concurrent calls during
77			* cancellation until state is set, to avoid surprising users
78			* during cancellation races.
79			*
80			* @param x the outcome
81			* @param mode the completion state value
82	jsr166	1.67	* @return true if this call caused transition from UNDECIDED to completed
83	dl	1.62	*/
84			private boolean setCompletion(Object x, int mode) {
85			Thread r = runner;
86			if (r == Thread.currentThread()) // null out runner on completion
87			UNSAFE.putObject(this, runnerOffset, r = null); // nonvolatile OK
88			int next = ((mode == INTERRUPTING) ? // set up transient states
89			(r != null) ? INTERRUPTING : CANCELLED :
90			(x != null) ? COMPLETING : mode);
91	jsr166	1.64	for (;;) {
92			int s = state;
93	jsr166	1.67	if (s == UNDECIDED) {
94			if (UNSAFE.compareAndSwapInt(this, stateOffset,
95			UNDECIDED, next)) {
96	dl	1.62	if (next == INTERRUPTING) {
97			Thread t = runner; // recheck
98			if (t != null)
99			t.interrupt();
100			state = CANCELLED;
101			}
102			else if (next == COMPLETING) {
103			outcome = x;
104			state = mode;
105			}
106			if (waiters != null)
107			releaseAll();
108			done();
109			return true;
110			}
111			}
112			else if (s == INTERRUPTING)
113	jsr166	1.64	Thread.yield(); // wait out pending cancellation interrupt
114	dl	1.62	else
115			return false;
116			}
117			}
118
119			/**
120	jsr166	1.64	* Returns result or throws exception for completed task.
121			*
122	dl	1.62	* @param s completed state value
123			*/
124			private V report(int s) throws ExecutionException {
125			Object x = outcome;
126			if (s == NORMAL)
127			return (V)x;
128			if ((s & (CANCELLED \| INTERRUPTING)) != 0)
129			throw new CancellationException();
130			throw new ExecutionException((Throwable)x);
131			}
132	dl	1.11
133	tim	1.1	/**
134	jsr166	1.64	* Creates a {@code FutureTask} that will, upon running, execute the
135			* given {@code Callable}.
136	tim	1.1	*
137			* @param callable the callable task
138	dl	1.9	* @throws NullPointerException if callable is null
139	tim	1.1	*/
140			public FutureTask(Callable<V> callable) {
141	dl	1.9	if (callable == null)
142			throw new NullPointerException();
143	dl	1.62	this.callable = callable;
144	tim	1.1	}
145
146			/**
147	jsr166	1.64	* Creates a {@code FutureTask} that will, upon running, execute the
148			* given {@code Runnable}, and arrange that {@code get} will return the
149	tim	1.1	* given result on successful completion.
150			*
151	jsr166	1.54	* @param runnable the runnable task
152	tim	1.1	* @param result the result to return on successful completion. If
153	dl	1.9	* you don't need a particular result, consider using
154	dl	1.16	* constructions of the form:
155	jsr166	1.58	* {@code Future<?> f = new FutureTask<Void>(runnable, null)}
156	dl	1.9	* @throws NullPointerException if runnable is null
157	tim	1.1	*/
158	dl	1.15	public FutureTask(Runnable runnable, V result) {
159	dl	1.62	this.callable = Executors.callable(runnable, result);
160	dl	1.20	}
161
162			public boolean isCancelled() {
163	dl	1.62	return (state & (CANCELLED \| INTERRUPTING)) != 0;
164	dl	1.20	}
165	jsr166	1.35
166	dl	1.20	public boolean isDone() {
167	jsr166	1.67	return state != UNDECIDED;
168	dl	1.13	}
169
170			public boolean cancel(boolean mayInterruptIfRunning) {
171	jsr166	1.67	return state == UNDECIDED &&
172	dl	1.62	setCompletion(null, mayInterruptIfRunning ?
173			INTERRUPTING : CANCELLED);
174	dl	1.13	}
175	jsr166	1.35
176	jsr166	1.43	/**
177			* @throws CancellationException {@inheritDoc}
178			*/
179	dl	1.2	public V get() throws InterruptedException, ExecutionException {
180	jsr166	1.64	int s = state;
181			if (s <= COMPLETING)
182			s = awaitDone(false, 0L);
183			return report(s);
184	tim	1.1	}
185
186	jsr166	1.43	/**
187			* @throws CancellationException {@inheritDoc}
188			*/
189	dl	1.2	public V get(long timeout, TimeUnit unit)
190	tim	1.1	throws InterruptedException, ExecutionException, TimeoutException {
191	jsr166	1.64	int s = state;
192			if (s <= COMPLETING &&
193			(s = awaitDone(true, unit.toNanos(timeout))) <= COMPLETING)
194	dl	1.62	throw new TimeoutException();
195			return report(s);
196	tim	1.1	}
197
198			/**
199	dl	1.20	* Protected method invoked when this task transitions to state
200	jsr166	1.64	* {@code isDone} (whether normally or via cancellation). The
201	dl	1.20	* default implementation does nothing. Subclasses may override
202			* this method to invoke completion callbacks or perform
203			* bookkeeping. Note that you can query status inside the
204			* implementation of this method to determine whether this task
205			* has been cancelled.
206			*/
207			protected void done() { }
208
209			/**
210	jsr166	1.64	* Sets the result of this future to the given value unless
211	dl	1.29	* this future has already been set or has been cancelled.
212	jsr166	1.64	*
213			* <p>This method is invoked internally by the {@link #run} method
214	dl	1.40	* upon successful completion of the computation.
215	jsr166	1.64	*
216	tim	1.1	* @param v the value
217	jsr166	1.35	*/
218	dl	1.2	protected void set(V v) {
219	dl	1.62	setCompletion(v, NORMAL);
220	tim	1.1	}
221
222			/**
223	jsr166	1.64	* Causes this future to report an {@link ExecutionException}
224			* with the given throwable as its cause, unless this future has
225	dl	1.24	* already been set or has been cancelled.
226	jsr166	1.64	*
227			* <p>This method is invoked internally by the {@link #run} method
228	dl	1.40	* upon failure of the computation.
229	jsr166	1.64	*
230	jsr166	1.41	* @param t the cause of failure
231	jsr166	1.35	*/
232	dl	1.2	protected void setException(Throwable t) {
233	dl	1.62	setCompletion(t, EXCEPTIONAL);
234	tim	1.1	}
235	jsr166	1.35
236	dl	1.24	public void run() {
237	jsr166	1.67	if (state == UNDECIDED &&
238	jsr166	1.65	UNSAFE.compareAndSwapObject(this, runnerOffset,
239			null, Thread.currentThread())) {
240	dl	1.62	V result;
241			try {
242			result = callable.call();
243			} catch (Throwable ex) {
244			setException(ex);
245			return;
246			}
247			set(result);
248			}
249	dl	1.24	}
250
251			/**
252	dl	1.30	* Executes the computation without setting its result, and then
253	jsr166	1.64	* resets this future to initial state, failing to do so if the
254	dl	1.24	* computation encounters an exception or is cancelled. This is
255			* designed for use with tasks that intrinsically execute more
256			* than once.
257	jsr166	1.64	*
258	dl	1.24	* @return true if successfully run and reset
259			*/
260			protected boolean runAndReset() {
261	jsr166	1.67	if (state != UNDECIDED \|\|
262	jsr166	1.66	!UNSAFE.compareAndSwapObject(this, runnerOffset,
263			null, Thread.currentThread()))
264	dl	1.62	return false;
265			try {
266			callable.call(); // don't set result
267			} catch (Throwable ex) {
268			setException(ex);
269			return false;
270			}
271			runner = null;
272			for (;;) {
273			int s = state;
274	jsr166	1.67	if (s == UNDECIDED)
275	dl	1.62	return true;
276			if (s != INTERRUPTING)
277			return false;
278	jsr166	1.64	Thread.yield(); // wait out pending cancellation interrupt
279	dl	1.62	}
280	dl	1.14	}
281	dl	1.3
282	dl	1.14	/**
283	dl	1.62	* Simple linked list nodes to record waiting threads in a Treiber
284	jsr166	1.64	* stack. See other classes such as Phaser and SynchronousQueue
285	dl	1.62	* for more detailed explanation.
286	dl	1.20	*/
287	dl	1.62	static final class WaitNode {
288			volatile Thread thread;
289			WaitNode next;
290			}
291	dl	1.42
292	dl	1.62	/**
293	jsr166	1.64	* Removes and signals all waiting threads.
294	dl	1.62	*/
295			private void releaseAll() {
296			WaitNode q;
297			while ((q = waiters) != null) {
298			if (UNSAFE.compareAndSwapObject(this, waitersOffset, q, null)) {
299			for (;;) {
300			Thread t = q.thread;
301			if (t != null) {
302			q.thread = null;
303			LockSupport.unpark(t);
304			}
305			WaitNode next = q.next;
306			if (next == null)
307			return;
308			q.next = null; // unlink to help gc
309			q = next;
310			}
311			}
312	dl	1.24	}
313	dl	1.62	}
314	dl	1.24
315	dl	1.62	/**
316	jsr166	1.64	* Awaits completion or aborts on interrupt or timeout.
317			*
318	dl	1.62	* @param timed true if use timed waits
319	jsr166	1.64	* @param nanos time to wait, if timed
320	dl	1.62	* @return state upon completion
321			*/
322			private int awaitDone(boolean timed, long nanos)
323			throws InterruptedException {
324	jsr166	1.63	long last = timed ? System.nanoTime() : 0L;
325	dl	1.62	WaitNode q = null;
326			boolean queued = false;
327	jsr166	1.64	for (;;) {
328	dl	1.62	if (Thread.interrupted()) {
329			removeWaiter(q);
330			throw new InterruptedException();
331			}
332	jsr166	1.64
333			int s = state;
334			if (s > COMPLETING) {
335	dl	1.62	if (q != null)
336			q.thread = null;
337			return s;
338			}
339			else if (q == null)
340			q = new WaitNode();
341			else if (!queued)
342			queued = UNSAFE.compareAndSwapObject(this, waitersOffset,
343			q.next = waiters, q);
344			else if (q.thread == null)
345			q.thread = Thread.currentThread();
346			else if (timed) {
347			long now = System.nanoTime();
348			if ((nanos -= (now - last)) <= 0L) {
349			removeWaiter(q);
350			return state;
351	dl	1.50	}
352	dl	1.62	last = now;
353			LockSupport.parkNanos(this, nanos);
354	dl	1.50	}
355	dl	1.62	else
356			LockSupport.park(this);
357	dl	1.24	}
358	dl	1.62	}
359	dl	1.24
360	dl	1.62	/**
361	jsr166	1.64	* Tries to unlink a timed-out or interrupted wait node to avoid
362			* accumulating garbage. Internal nodes are simply unspliced
363	dl	1.62	* without CAS since it is harmless if they are traversed anyway
364			* by releasers or concurrent calls to removeWaiter.
365			*/
366			private void removeWaiter(WaitNode node) {
367			if (node != null) {
368			node.thread = null;
369			WaitNode pred = null;
370			WaitNode q = waiters;
371			while (q != null) {
372			WaitNode next = node.next;
373			if (q != node) {
374			pred = q;
375			q = next;
376	dl	1.50	}
377	dl	1.62	else if (pred != null) {
378			pred.next = next;
379			break;
380	dl	1.50	}
381	dl	1.62	else if (UNSAFE.compareAndSwapObject(this, waitersOffset,
382			q, next))
383	jsr166	1.56	break;
384	dl	1.62	else { // restart on CAS failure
385			pred = null;
386			q = waiters;
387	jsr166	1.55	}
388	jsr166	1.56	}
389	dl	1.14	}
390	dl	1.62	}
391	dl	1.14
392	dl	1.62	// Unsafe mechanics
393			private static final sun.misc.Unsafe UNSAFE;
394			private static final long stateOffset;
395			private static final long runnerOffset;
396			private static final long waitersOffset;
397			static {
398			try {
399			UNSAFE = sun.misc.Unsafe.getUnsafe();
400			Class<?> k = FutureTask.class;
401			stateOffset = UNSAFE.objectFieldOffset
402			(k.getDeclaredField("state"));
403			runnerOffset = UNSAFE.objectFieldOffset
404			(k.getDeclaredField("runner"));
405			waitersOffset = UNSAFE.objectFieldOffset
406			(k.getDeclaredField("waiters"));
407			} catch (Exception e) {
408			throw new Error(e);
409	dl	1.14	}
410	dl	1.15	}
411	dl	1.62
412	dl	1.15	}