util/concurrent/CyclicBarrier.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.Condition;
import java.util.concurrent.locks.ReentrantLock;

/**
 * A synchronization aid that allows a set of threads to all wait for
 * each other to reach a common barrier point.  CyclicBarriers are
 * useful in programs involving a fixed sized party of threads that
 * must occasionally wait for each other. The barrier is called
 * <em>cyclic</em> because it can be re-used after the waiting threads
 * are released.
 *
 * <p>A <tt>CyclicBarrier</tt> supports an optional {@link Runnable} command
 * that is run once per barrier point, after the last thread in the party
 * arrives, but before any threads are released.
 * This <em>barrier action</em> is useful
 * for updating shared-state before any of the parties continue.
 *
 * <p><b>Sample usage:</b> Here is an example of
 *  using a barrier in a parallel decomposition design:
 *
 *  <pre> {@code
 * class Solver {
 *   final int N;
 *   final float[][] data;
 *   final CyclicBarrier barrier;
 *
 *   class Worker implements Runnable {
 *     int myRow;
 *     Worker(int row) { myRow = row; }
 *     public void run() {
 *       while (!done()) {
 *         processRow(myRow);
 *
 *         try {
 *           barrier.await();
 *         } catch (InterruptedException ex) {
 *           return;
 *         } catch (BrokenBarrierException ex) {
 *           return;
 *         }
 *       }
 *     }
 *   }
 *
 *   public Solver(float[][] matrix) {
 *     data = matrix;
 *     N = matrix.length;
 *     barrier = new CyclicBarrier(N,
 *                                 new Runnable() {
 *                                   public void run() {
 *                                     mergeRows(...);
 *                                   }
 *                                 });
 *     for (int i = 0; i < N; ++i)
 *       new Thread(new Worker(i)).start();
 *
 *     waitUntilDone();
 *   }
 * }}</pre>
 *
 * Here, each worker thread processes a row of the matrix then waits at the
 * barrier until all rows have been processed. When all rows are processed
 * the supplied {@link Runnable} barrier action is executed and merges the
 * rows. If the merger
 * determines that a solution has been found then <tt>done()</tt> will return
 * <tt>true</tt> and each worker will terminate.
 *
 * <p>If the barrier action does not rely on the parties being suspended when
 * it is executed, then any of the threads in the party could execute that
 * action when it is released. To facilitate this, each invocation of
 * {@link #await} returns the arrival index of that thread at the barrier.
 * You can then choose which thread should execute the barrier action, for
 * example:
 *  <pre> {@code
 * if (barrier.await() == 0) {
 *   // log the completion of this iteration
 * }}</pre>
 *
 * <p>The <tt>CyclicBarrier</tt> uses an all-or-none breakage model
 * for failed synchronization attempts: If a thread leaves a barrier
 * point prematurely because of interruption, failure, or timeout, all
 * other threads waiting at that barrier point will also leave
 * abnormally via {@link BrokenBarrierException} (or
 * {@link InterruptedException} if they too were interrupted at about
 * the same time).
 *
 * <p>Memory consistency effects: Actions in a thread prior to calling
 * {@code await()}
 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * actions that are part of the barrier action, which in turn
 * <i>happen-before</i> actions following a successful return from the
 * corresponding {@code await()} in other threads.
 *
 * @since 1.5
 * @see CountDownLatch
 *
 * @author Doug Lea
 */
public class CyclicBarrier {
    /**
     * Each use of the barrier is represented as a generation instance.
     * The generation changes whenever the barrier is tripped, or
     * is reset. There can be many generations associated with threads
     * using the barrier - due to the non-deterministic way the lock
     * may be allocated to waiting threads - but only one of these
     * can be active at a time (the one to which <tt>count</tt> applies)
     * and all the rest are either broken or tripped.
     * There need not be an active generation if there has been a break
     * but no subsequent reset.
     */
    private static class Generation {
        boolean broken = false;
    }

    /** The lock for guarding barrier entry */
    private final ReentrantLock lock = new ReentrantLock();
    /** Condition to wait on until tripped */
    private final Condition trip = lock.newCondition();
    /** The number of parties */
    private final int parties;
    /* The command to run when tripped */
    private final Runnable barrierCommand;
    /** The current generation */
    private Generation generation = new Generation();

    /**
     * Number of parties still waiting. Counts down from parties to 0
     * on each generation.  It is reset to parties on each new
     * generation or when broken.
     */
    private int count;

    /**
     * Updates state on barrier trip and wakes up everyone.
     * Called only while holding lock.
     */
    private void nextGeneration() {
        // signal completion of last generation
        trip.signalAll();
        // set up next generation
        count = parties;
        generation = new Generation();
    }

    /**
     * Sets current barrier generation as broken and wakes up everyone.
     * Called only while holding lock.
     */
    private void breakBarrier() {
        generation.broken = true;
        count = parties;
        trip.signalAll();
    }

    /**
     * Main barrier code, covering the various policies.
     */
    private int dowait(boolean timed, long nanos)
        throws InterruptedException, BrokenBarrierException,
               TimeoutException {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            final Generation g = generation;

            if (g.broken)
                throw new BrokenBarrierException();

            if (Thread.interrupted()) {
                breakBarrier();
                throw new InterruptedException();
            }

            int index = --count;
            if (index == 0) {  // tripped
                boolean ranAction = false;
                try {
                    final Runnable command = barrierCommand;
                    if (command != null)
                        command.run();
                    ranAction = true;
                    nextGeneration();
                    return 0;
                } finally {
                    if (!ranAction)
                        breakBarrier();
                }
            }

            // loop until tripped, broken, interrupted, or timed out
            for (;;) {
                try {
                    if (!timed)
                        trip.await();
                    else if (nanos > 0L)
                        nanos = trip.awaitNanos(nanos);
                } catch (InterruptedException ie) {
                    if (g == generation && ! g.broken) {
                        breakBarrier();
                        throw ie;
                    } else {
                        // We're about to finish waiting even if we had not
                        // been interrupted, so this interrupt is deemed to
                        // "belong" to subsequent execution.
                        Thread.currentThread().interrupt();
                    }
                }

                if (g.broken)
                    throw new BrokenBarrierException();

                if (g != generation)
                    return index;

                if (timed && nanos <= 0L) {
                    breakBarrier();
                    throw new TimeoutException();
                }
            }
        } finally {
            lock.unlock();
        }
    }

    /**
     * Creates a new <tt>CyclicBarrier</tt> that will trip when the
     * given number of parties (threads) are waiting upon it, and which
     * will execute the given barrier action when the barrier is tripped,
     * performed by the last thread entering the barrier.
     *
     * @param parties the number of threads that must invoke {@link #await}
     *        before the barrier is tripped
     * @param barrierAction the command to execute when the barrier is
     *        tripped, or {@code null} if there is no action
     * @throws IllegalArgumentException if {@code parties} is less than 1
     */
    public CyclicBarrier(int parties, Runnable barrierAction) {
        if (parties <= 0) throw new IllegalArgumentException();
        this.parties = parties;
        this.count = parties;
        this.barrierCommand = barrierAction;
    }

    /**
     * Creates a new <tt>CyclicBarrier</tt> that will trip when the
     * given number of parties (threads) are waiting upon it, and
     * does not perform a predefined action when the barrier is tripped.
     *
     * @param parties the number of threads that must invoke {@link #await}
     *        before the barrier is tripped
     * @throws IllegalArgumentException if {@code parties} is less than 1
     */
    public CyclicBarrier(int parties) {
        this(parties, null);
    }

    /**
     * Returns the number of parties required to trip this barrier.
     *
     * @return the number of parties required to trip this barrier
     */
    public int getParties() {
        return parties;
    }

    /**
     * Waits until all {@linkplain #getParties parties} have invoked
     * <tt>await</tt> on this barrier.
     *
     * <p>If the current thread is not the last to arrive then it is
     * disabled for thread scheduling purposes and lies dormant until
     * one of the following things happens:
     * <ul>
     * <li>The last thread arrives; or
     * <li>Some other thread {@linkplain Thread#interrupt interrupts}
     * the current thread; or
     * <li>Some other thread {@linkplain Thread#interrupt interrupts}
     * one of the other waiting threads; or
     * <li>Some other thread times out while waiting for barrier; or
     * <li>Some other thread invokes {@link #reset} on this barrier.
     * </ul>
     *
     * <p>If the current thread:
     * <ul>
     * <li>has its interrupted status set on entry to this method; or
     * <li>is {@linkplain Thread#interrupt interrupted} while waiting
     * </ul>
     * then {@link InterruptedException} is thrown and the current thread's
     * interrupted status is cleared.
     *
     * <p>If the barrier is {@link #reset} while any thread is waiting,
     * or if the barrier {@linkplain #isBroken is broken} when
     * <tt>await</tt> is invoked, or while any thread is waiting, then
     * {@link BrokenBarrierException} is thrown.
     *
     * <p>If any thread is {@linkplain Thread#interrupt interrupted} while waiting,
     * then all other waiting threads will throw
     * {@link BrokenBarrierException} and the barrier is placed in the broken
     * state.
     *
     * <p>If the current thread is the last thread to arrive, and a
     * non-null barrier action was supplied in the constructor, then the
     * current thread runs the action before allowing the other threads to
     * continue.
     * If an exception occurs during the barrier action then that exception
     * will be propagated in the current thread and the barrier is placed in
     * the broken state.
     *
     * @return the arrival index of the current thread, where index
     *         <tt>{@link #getParties()} - 1</tt> indicates the first
     *         to arrive and zero indicates the last to arrive
     * @throws InterruptedException if the current thread was interrupted
     *         while waiting
     * @throws BrokenBarrierException if <em>another</em> thread was
     *         interrupted or timed out while the current thread was
     *         waiting, or the barrier was reset, or the barrier was
     *         broken when {@code await} was called, or the barrier
     *         action (if present) failed due an exception.
     */
    public int await() throws InterruptedException, BrokenBarrierException {
        try {
            return dowait(false, 0L);
        } catch (TimeoutException toe) {
            throw new Error(toe); // cannot happen
        }
    }

    /**
     * Waits until all {@linkplain #getParties parties} have invoked
     * <tt>await</tt> on this barrier, or the specified waiting time elapses.
     *
     * <p>If the current thread is not the last to arrive then it is
     * disabled for thread scheduling purposes and lies dormant until
     * one of the following things happens:
     * <ul>
     * <li>The last thread arrives; or
     * <li>The specified timeout elapses; or
     * <li>Some other thread {@linkplain Thread#interrupt interrupts}
     * the current thread; or
     * <li>Some other thread {@linkplain Thread#interrupt interrupts}
     * one of the other waiting threads; or
     * <li>Some other thread times out while waiting for barrier; or
     * <li>Some other thread invokes {@link #reset} on this barrier.
     * </ul>
     *
     * <p>If the current thread:
     * <ul>
     * <li>has its interrupted status set on entry to this method; or
     * <li>is {@linkplain Thread#interrupt interrupted} while waiting
     * </ul>
     * then {@link InterruptedException} is thrown and the current thread's
     * interrupted status is cleared.
     *
     * <p>If the specified waiting time elapses then {@link TimeoutException}
     * is thrown. If the time is less than or equal to zero, the
     * method will not wait at all.
     *
     * <p>If the barrier is {@link #reset} while any thread is waiting,
     * or if the barrier {@linkplain #isBroken is broken} when
     * <tt>await</tt> is invoked, or while any thread is waiting, then
     * {@link BrokenBarrierException} is thrown.
     *
     * <p>If any thread is {@linkplain Thread#interrupt interrupted} while
     * waiting, then all other waiting threads will throw {@link
     * BrokenBarrierException} and the barrier is placed in the broken
     * state.
     *
     * <p>If the current thread is the last thread to arrive, and a
     * non-null barrier action was supplied in the constructor, then the
     * current thread runs the action before allowing the other threads to
     * continue.
     * If an exception occurs during the barrier action then that exception
     * will be propagated in the current thread and the barrier is placed in
     * the broken state.
     *
     * @param timeout the time to wait for the barrier
     * @param unit the time unit of the timeout parameter
     * @return the arrival index of the current thread, where index
     *         <tt>{@link #getParties()} - 1</tt> indicates the first
     *         to arrive and zero indicates the last to arrive
     * @throws InterruptedException if the current thread was interrupted
     *         while waiting
     * @throws TimeoutException if the specified timeout elapses
     * @throws BrokenBarrierException if <em>another</em> thread was
     *         interrupted or timed out while the current thread was
     *         waiting, or the barrier was reset, or the barrier was broken
     *         when {@code await} was called, or the barrier action (if
     *         present) failed due an exception
     */
    public int await(long timeout, TimeUnit unit)
        throws InterruptedException,
               BrokenBarrierException,
               TimeoutException {
        return dowait(true, unit.toNanos(timeout));
    }

    /**
     * Queries if this barrier is in a broken state.
     *
     * @return {@code true} if one or more parties broke out of this
     *         barrier due to interruption or timeout since
     *         construction or the last reset, or a barrier action
     *         failed due to an exception; {@code false} otherwise.
     */
    public boolean isBroken() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return generation.broken;
        } finally {
            lock.unlock();
        }
    }

    /**
     * Resets the barrier to its initial state.  If any parties are
     * currently waiting at the barrier, they will return with a
     * {@link BrokenBarrierException}. Note that resets <em>after</em>
     * a breakage has occurred for other reasons can be complicated to
     * carry out; threads need to re-synchronize in some other way,
     * and choose one to perform the reset.  It may be preferable to
     * instead create a new barrier for subsequent use.
     */
    public void reset() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            breakBarrier();   // break the current generation
            nextGeneration(); // start a new generation
        } finally {
            lock.unlock();
        }
    }

    /**
     * Returns the number of parties currently waiting at the barrier.
     * This method is primarily useful for debugging and assertions.
     *
     * @return the number of parties currently blocked in {@link #await}
     */
    public int getNumberWaiting() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return parties - count;
        } finally {
            lock.unlock();
        }
    }
}
Revision:	1.1
Committed:	Sun Dec 16 20:55:15 2012 UTC (11 years, 5 months ago) by dl
Branch:	MAIN
Log Message:	Create src/jdk7 package
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/publicdomain/zero/1.0/
5	*/
6
7	package java.util.concurrent;
8	import java.util.concurrent.locks.Condition;
9	import java.util.concurrent.locks.ReentrantLock;
10
11	/**
12	* A synchronization aid that allows a set of threads to all wait for
13	* each other to reach a common barrier point. CyclicBarriers are
14	* useful in programs involving a fixed sized party of threads that
15	* must occasionally wait for each other. The barrier is called
16	* <em>cyclic</em> because it can be re-used after the waiting threads
17	* are released.
18	*
19	* <p>A <tt>CyclicBarrier</tt> supports an optional {@link Runnable} command
20	* that is run once per barrier point, after the last thread in the party
21	* arrives, but before any threads are released.
22	* This <em>barrier action</em> is useful
23	* for updating shared-state before any of the parties continue.
24	*
25	* <p><b>Sample usage:</b> Here is an example of
26	* using a barrier in a parallel decomposition design:
27	*
28	* <pre> {@code
29	* class Solver {
30	* final int N;
31	* final float[][] data;
32	* final CyclicBarrier barrier;
33	*
34	* class Worker implements Runnable {
35	* int myRow;
36	* Worker(int row) { myRow = row; }
37	* public void run() {
38	* while (!done()) {
39	* processRow(myRow);
40	*
41	* try {
42	* barrier.await();
43	* } catch (InterruptedException ex) {
44	* return;
45	* } catch (BrokenBarrierException ex) {
46	* return;
47	* }
48	* }
49	* }
50	* }
51	*
52	* public Solver(float[][] matrix) {
53	* data = matrix;
54	* N = matrix.length;
55	* barrier = new CyclicBarrier(N,
56	* new Runnable() {
57	* public void run() {
58	* mergeRows(...);
59	* }
60	* });
61	* for (int i = 0; i < N; ++i)
62	* new Thread(new Worker(i)).start();
63	*
64	* waitUntilDone();
65	* }
66	* }}</pre>
67	*
68	* Here, each worker thread processes a row of the matrix then waits at the
69	* barrier until all rows have been processed. When all rows are processed
70	* the supplied {@link Runnable} barrier action is executed and merges the
71	* rows. If the merger
72	* determines that a solution has been found then <tt>done()</tt> will return
73	* <tt>true</tt> and each worker will terminate.
74	*
75	* <p>If the barrier action does not rely on the parties being suspended when
76	* it is executed, then any of the threads in the party could execute that
77	* action when it is released. To facilitate this, each invocation of
78	* {@link #await} returns the arrival index of that thread at the barrier.
79	* You can then choose which thread should execute the barrier action, for
80	* example:
81	* <pre> {@code
82	* if (barrier.await() == 0) {
83	* // log the completion of this iteration
84	* }}</pre>
85	*
86	* <p>The <tt>CyclicBarrier</tt> uses an all-or-none breakage model
87	* for failed synchronization attempts: If a thread leaves a barrier
88	* point prematurely because of interruption, failure, or timeout, all
89	* other threads waiting at that barrier point will also leave
90	* abnormally via {@link BrokenBarrierException} (or
91	* {@link InterruptedException} if they too were interrupted at about
92	* the same time).
93	*
94	* <p>Memory consistency effects: Actions in a thread prior to calling
95	* {@code await()}
96	* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
97	* actions that are part of the barrier action, which in turn
98	* <i>happen-before</i> actions following a successful return from the
99	* corresponding {@code await()} in other threads.
100	*
101	* @since 1.5
102	* @see CountDownLatch
103	*
104	* @author Doug Lea
105	*/
106	public class CyclicBarrier {
107	/**
108	* Each use of the barrier is represented as a generation instance.
109	* The generation changes whenever the barrier is tripped, or
110	* is reset. There can be many generations associated with threads
111	* using the barrier - due to the non-deterministic way the lock
112	* may be allocated to waiting threads - but only one of these
113	* can be active at a time (the one to which <tt>count</tt> applies)
114	* and all the rest are either broken or tripped.
115	* There need not be an active generation if there has been a break
116	* but no subsequent reset.
117	*/
118	private static class Generation {
119	boolean broken = false;
120	}
121
122	/** The lock for guarding barrier entry */
123	private final ReentrantLock lock = new ReentrantLock();
124	/** Condition to wait on until tripped */
125	private final Condition trip = lock.newCondition();
126	/** The number of parties */
127	private final int parties;
128	/* The command to run when tripped */
129	private final Runnable barrierCommand;
130	/** The current generation */
131	private Generation generation = new Generation();
132
133	/**
134	* Number of parties still waiting. Counts down from parties to 0
135	* on each generation. It is reset to parties on each new
136	* generation or when broken.
137	*/
138	private int count;
139
140	/**
141	* Updates state on barrier trip and wakes up everyone.
142	* Called only while holding lock.
143	*/
144	private void nextGeneration() {
145	// signal completion of last generation
146	trip.signalAll();
147	// set up next generation
148	count = parties;
149	generation = new Generation();
150	}
151
152	/**
153	* Sets current barrier generation as broken and wakes up everyone.
154	* Called only while holding lock.
155	*/
156	private void breakBarrier() {
157	generation.broken = true;
158	count = parties;
159	trip.signalAll();
160	}
161
162	/**
163	* Main barrier code, covering the various policies.
164	*/
165	private int dowait(boolean timed, long nanos)
166	throws InterruptedException, BrokenBarrierException,
167	TimeoutException {
168	final ReentrantLock lock = this.lock;
169	lock.lock();
170	try {
171	final Generation g = generation;
172
173	if (g.broken)
174	throw new BrokenBarrierException();
175
176	if (Thread.interrupted()) {
177	breakBarrier();
178	throw new InterruptedException();
179	}
180
181	int index = --count;
182	if (index == 0) { // tripped
183	boolean ranAction = false;
184	try {
185	final Runnable command = barrierCommand;
186	if (command != null)
187	command.run();
188	ranAction = true;
189	nextGeneration();
190	return 0;
191	} finally {
192	if (!ranAction)
193	breakBarrier();
194	}
195	}
196
197	// loop until tripped, broken, interrupted, or timed out
198	for (;;) {
199	try {
200	if (!timed)
201	trip.await();
202	else if (nanos > 0L)
203	nanos = trip.awaitNanos(nanos);
204	} catch (InterruptedException ie) {
205	if (g == generation && ! g.broken) {
206	breakBarrier();
207	throw ie;
208	} else {
209	// We're about to finish waiting even if we had not
210	// been interrupted, so this interrupt is deemed to
211	// "belong" to subsequent execution.
212	Thread.currentThread().interrupt();
213	}
214	}
215
216	if (g.broken)
217	throw new BrokenBarrierException();
218
219	if (g != generation)
220	return index;
221
222	if (timed && nanos <= 0L) {
223	breakBarrier();
224	throw new TimeoutException();
225	}
226	}
227	} finally {
228	lock.unlock();
229	}
230	}
231
232	/**
233	* Creates a new <tt>CyclicBarrier</tt> that will trip when the
234	* given number of parties (threads) are waiting upon it, and which
235	* will execute the given barrier action when the barrier is tripped,
236	* performed by the last thread entering the barrier.
237	*
238	* @param parties the number of threads that must invoke {@link #await}
239	* before the barrier is tripped
240	* @param barrierAction the command to execute when the barrier is
241	* tripped, or {@code null} if there is no action
242	* @throws IllegalArgumentException if {@code parties} is less than 1
243	*/
244	public CyclicBarrier(int parties, Runnable barrierAction) {
245	if (parties <= 0) throw new IllegalArgumentException();
246	this.parties = parties;
247	this.count = parties;
248	this.barrierCommand = barrierAction;
249	}
250
251	/**
252	* Creates a new <tt>CyclicBarrier</tt> that will trip when the
253	* given number of parties (threads) are waiting upon it, and
254	* does not perform a predefined action when the barrier is tripped.
255	*
256	* @param parties the number of threads that must invoke {@link #await}
257	* before the barrier is tripped
258	* @throws IllegalArgumentException if {@code parties} is less than 1
259	*/
260	public CyclicBarrier(int parties) {
261	this(parties, null);
262	}
263
264	/**
265	* Returns the number of parties required to trip this barrier.
266	*
267	* @return the number of parties required to trip this barrier
268	*/
269	public int getParties() {
270	return parties;
271	}
272
273	/**
274	* Waits until all {@linkplain #getParties parties} have invoked
275	* <tt>await</tt> on this barrier.
276	*
277	* <p>If the current thread is not the last to arrive then it is
278	* disabled for thread scheduling purposes and lies dormant until
279	* one of the following things happens:
280	* <ul>
281	* <li>The last thread arrives; or
282	* <li>Some other thread {@linkplain Thread#interrupt interrupts}
283	* the current thread; or
284	* <li>Some other thread {@linkplain Thread#interrupt interrupts}
285	* one of the other waiting threads; or
286	* <li>Some other thread times out while waiting for barrier; or
287	* <li>Some other thread invokes {@link #reset} on this barrier.
288	* </ul>
289	*
290	* <p>If the current thread:
291	* <ul>
292	* <li>has its interrupted status set on entry to this method; or
293	* <li>is {@linkplain Thread#interrupt interrupted} while waiting
294	* </ul>
295	* then {@link InterruptedException} is thrown and the current thread's
296	* interrupted status is cleared.
297	*
298	* <p>If the barrier is {@link #reset} while any thread is waiting,
299	* or if the barrier {@linkplain #isBroken is broken} when
300	* <tt>await</tt> is invoked, or while any thread is waiting, then
301	* {@link BrokenBarrierException} is thrown.
302	*
303	* <p>If any thread is {@linkplain Thread#interrupt interrupted} while waiting,
304	* then all other waiting threads will throw
305	* {@link BrokenBarrierException} and the barrier is placed in the broken
306	* state.
307	*
308	* <p>If the current thread is the last thread to arrive, and a
309	* non-null barrier action was supplied in the constructor, then the
310	* current thread runs the action before allowing the other threads to
311	* continue.
312	* If an exception occurs during the barrier action then that exception
313	* will be propagated in the current thread and the barrier is placed in
314	* the broken state.
315	*
316	* @return the arrival index of the current thread, where index
317	* <tt>{@link #getParties()} - 1</tt> indicates the first
318	* to arrive and zero indicates the last to arrive
319	* @throws InterruptedException if the current thread was interrupted
320	* while waiting
321	* @throws BrokenBarrierException if <em>another</em> thread was
322	* interrupted or timed out while the current thread was
323	* waiting, or the barrier was reset, or the barrier was
324	* broken when {@code await} was called, or the barrier
325	* action (if present) failed due an exception.
326	*/
327	public int await() throws InterruptedException, BrokenBarrierException {
328	try {
329	return dowait(false, 0L);
330	} catch (TimeoutException toe) {
331	throw new Error(toe); // cannot happen
332	}
333	}
334
335	/**
336	* Waits until all {@linkplain #getParties parties} have invoked
337	* <tt>await</tt> on this barrier, or the specified waiting time elapses.
338	*
339	* <p>If the current thread is not the last to arrive then it is
340	* disabled for thread scheduling purposes and lies dormant until
341	* one of the following things happens:
342	* <ul>
343	* <li>The last thread arrives; or
344	* <li>The specified timeout elapses; or
345	* <li>Some other thread {@linkplain Thread#interrupt interrupts}
346	* the current thread; or
347	* <li>Some other thread {@linkplain Thread#interrupt interrupts}
348	* one of the other waiting threads; or
349	* <li>Some other thread times out while waiting for barrier; or
350	* <li>Some other thread invokes {@link #reset} on this barrier.
351	* </ul>
352	*
353	* <p>If the current thread:
354	* <ul>
355	* <li>has its interrupted status set on entry to this method; or
356	* <li>is {@linkplain Thread#interrupt interrupted} while waiting
357	* </ul>
358	* then {@link InterruptedException} is thrown and the current thread's
359	* interrupted status is cleared.
360	*
361	* <p>If the specified waiting time elapses then {@link TimeoutException}
362	* is thrown. If the time is less than or equal to zero, the
363	* method will not wait at all.
364	*
365	* <p>If the barrier is {@link #reset} while any thread is waiting,
366	* or if the barrier {@linkplain #isBroken is broken} when
367	* <tt>await</tt> is invoked, or while any thread is waiting, then
368	* {@link BrokenBarrierException} is thrown.
369	*
370	* <p>If any thread is {@linkplain Thread#interrupt interrupted} while
371	* waiting, then all other waiting threads will throw {@link
372	* BrokenBarrierException} and the barrier is placed in the broken
373	* state.
374	*
375	* <p>If the current thread is the last thread to arrive, and a
376	* non-null barrier action was supplied in the constructor, then the
377	* current thread runs the action before allowing the other threads to
378	* continue.
379	* If an exception occurs during the barrier action then that exception
380	* will be propagated in the current thread and the barrier is placed in
381	* the broken state.
382	*
383	* @param timeout the time to wait for the barrier
384	* @param unit the time unit of the timeout parameter
385	* @return the arrival index of the current thread, where index
386	* <tt>{@link #getParties()} - 1</tt> indicates the first
387	* to arrive and zero indicates the last to arrive
388	* @throws InterruptedException if the current thread was interrupted
389	* while waiting
390	* @throws TimeoutException if the specified timeout elapses
391	* @throws BrokenBarrierException if <em>another</em> thread was
392	* interrupted or timed out while the current thread was
393	* waiting, or the barrier was reset, or the barrier was broken
394	* when {@code await} was called, or the barrier action (if
395	* present) failed due an exception
396	*/
397	public int await(long timeout, TimeUnit unit)
398	throws InterruptedException,
399	BrokenBarrierException,
400	TimeoutException {
401	return dowait(true, unit.toNanos(timeout));
402	}
403
404	/**
405	* Queries if this barrier is in a broken state.
406	*
407	* @return {@code true} if one or more parties broke out of this
408	* barrier due to interruption or timeout since
409	* construction or the last reset, or a barrier action
410	* failed due to an exception; {@code false} otherwise.
411	*/
412	public boolean isBroken() {
413	final ReentrantLock lock = this.lock;
414	lock.lock();
415	try {
416	return generation.broken;
417	} finally {
418	lock.unlock();
419	}
420	}
421
422	/**
423	* Resets the barrier to its initial state. If any parties are
424	* currently waiting at the barrier, they will return with a
425	* {@link BrokenBarrierException}. Note that resets <em>after</em>
426	* a breakage has occurred for other reasons can be complicated to
427	* carry out; threads need to re-synchronize in some other way,
428	* and choose one to perform the reset. It may be preferable to
429	* instead create a new barrier for subsequent use.
430	*/
431	public void reset() {
432	final ReentrantLock lock = this.lock;
433	lock.lock();
434	try {
435	breakBarrier(); // break the current generation
436	nextGeneration(); // start a new generation
437	} finally {
438	lock.unlock();
439	}
440	}
441
442	/**
443	* Returns the number of parties currently waiting at the barrier.
444	* This method is primarily useful for debugging and assertions.
445	*
446	* @return the number of parties currently blocked in {@link #await}
447	*/
448	public int getNumberWaiting() {
449	final ReentrantLock lock = this.lock;
450	lock.lock();
451	try {
452	return parties - count;
453	} finally {
454	lock.unlock();
455	}
456	}
457	}