util/concurrent/CyclicBarrier.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain. Use, modify, and
 * redistribute this code in any way without acknowledgement.
 */

package java.util.concurrent;

/**
 * A <tt>CyclicBarrier</tt> allows a set threads to all wait for each 
 * other to reach a common barrier point.  They are useful in programs
 * involving a fixed sized party of threads that must occasionally
 * wait for each other. The barrier is <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 a code sketch of 
 *  using a barrier in a parallel decomposition design:
 * <pre>
 * 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>  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 or timeout, all others
 * will also leave abnormally (via {@link BrokenBarrierException}),
 * until the barrier is {@link #reset}. This is usually the simplest
 * and best strategy for sharing knowledge about failures among
 * cooperating threads in the most common usage contexts of barriers.
 *
 * <h3>Implementation Considerations</h3>
 * <p>This implementation has the property that interruptions among newly
 * arriving threads can cause as-yet-unresumed threads from a previous
 * barrier cycle to return out as broken. This transmits breakage as
 * early as possible, but with the possible byproduct that only some
 * threads returning out of a barrier will realize that it is newly
 * broken. (Others will not realize this until a future cycle.)
 *
 *
 *
 * @since 1.5
 * @spec JSR-166
 * @revised $Date: 2003/01/28 06:56:53 $
 * @editor $Author: dholmes $
 *
 * @fixme Is the above property actually true in this implementation?
 * @fixme Should we have a timeout version of await()?
 */
public class CyclicBarrier {
    private final ReentrantLock lock = new ReentrantLock();
    private final Condition trip = lock.newCondition();
    private final int parties;
    private Runnable barrierCommand;

    /**
     * The generation number. Incremented mod Integer.MAX_VALUE every
     * time barrier tripped. Starts at 1 to simplify handling of
     * breakage indicator
     */
    private int generation = 1; 

    /** 
     * Breakage indicator: last generation of breakage, propagated
     * across barrier generations until reset. 
     */
    private int broken = 0; 

    /**
     * Number of parties still waiting. Counts down from parties to 0
     * on each cycle.
     */
    private int count; 

    /**
     * Update state on barrier trip.
     */  
    private void nextGeneration() {
        count = parties;
        int g = generation;
        // avoid generation == 0
        if (++generation < 0) generation = 1;
        // propagate breakage
        if (broken == g) broken = generation;
    }

    private int dowait(boolean timed, long nanos) throws InterruptedException, BrokenBarrierException, TimeoutException {
        lock.lock();
        try {
            int index = --count;
            int g = generation;

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

            if (Thread.interrupted()) {
                broken = g;
                trip.signalAll();
                throw new InterruptedException();
            }

            if (index == 0) {  // tripped
                nextGeneration();
                trip.signalAll();
                try {
                    if (barrierCommand != null) 
                        barrierCommand.run();
                    return 0;
                }
                catch (RuntimeException ex) {
                    broken = generation; // next generation is broken
                    throw ex;
                }
            }

            while (generation == g) {
                try {
                    if (!timed) 
                        trip.await();
                    else if (nanos > 0)
                        nanos = trip.awaitNanos(nanos);
                }
                catch (InterruptedException ex) {
                    // Only claim that broken if interrupted before reset
                    if (generation == g) { 
                        broken = g;
                        trip.signalAll();
                        throw ex;
                    }
                    else {
                        Thread.currentThread().interrupt(); // propagate
                        break;
                    }
                }
                
                if (timed && nanos <= 0) {
                    broken = g;
                    trip.signalAll();
                    throw new TimeoutException();
                }

                if (broken == generation) 
                    throw new BrokenBarrierException();
                
            }
            return index;

        }
        finally {
            lock.unlock();
        }
    }

    /**
     * Create 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.
     *
     * @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.
     *
     * @throws IllegalArgumentException if <tt>parties</tt> 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;
    }

    /**
     * Create a new <tt>CyclicBarrier</tt> that will trip when the
     * given number of parties (threads) are waiting upon it.
     *
     * <p>This is equivalent to <tt>CyclicBarrier(parties, null)</tt>.
     *
     * @param parties the number of threads that must invoke {@link #await}
     * before the barrier is tripped.
     *
     * @throws IllegalArgumentException if <tt>parties</tt> is less than 1.
     */
    public CyclicBarrier(int parties) {
        this(parties, null);
    }

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

    /**
     * Wait until all {@link #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 following things happens:
     * <ul>
     * <li>The last thread arrives; or
     * <li>Some other thread {@link Thread#interrupt interrupts} the current
     * thread; or
     * <li>Some other thread  {@link 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 {@link 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 {@link #isBroken is broken} when <tt>await</tt> is invoked
     * then {@link BrokenBarrierException} is thrown.
     *
     * <p>If any thread is {@link 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.
     *
     * @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 while the current thread was waiting, or the barrier was
     * reset, or the barrier was broken when <tt>await</tt> was called.
     */
    public int await() throws InterruptedException, BrokenBarrierException {
        try {
            return dowait(false, 0);
        }
        catch (TimeoutException toe) {
            throw new Error(toe); // cannot happen;
        }
    }

    /**
     * Wait until all {@link #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>The speceified timeout elapses; or
     * <li>Some other thread {@link Thread#interrupt interrupts} the current
     * thread; or
     * <li>Some other thread  {@link 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 {@link 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 {@link #isBroken is broken} when <tt>await</tt> is invoked
     * then {@link BrokenBarrierException} is thrown.
     *
     * <p>If any thread is {@link 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.
     *
     * @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 while the current thread was waiting, or the barrier was
     * reset, or the barrier was broken when <tt>await</tt> was called.
     */
    public int await(long timeout, TimeUnit unit) throws InterruptedException, BrokenBarrierException, TimeoutException {
        return dowait(true, unit.toNanos(timeout));
    }

    /**
     * Query if this barrier is in a broken state.
     * @return <tt>true</tt> if one or more parties broke out of this
     * barrier due to interruption or timeout since construction or
     * the last reset; and <tt>false</tt> otherwise.
     */
    public boolean isBroken() {
        lock.lock();
        try {
            return broken >= generation;
        }
        finally {
            lock.unlock();
        }
    }

    /**
     * Reset the barrier to its initial state.  If any parties are
     * currently waiting at the barrier, they will return with a
     * {@link BrokenBarrierException}.
     */
    public void reset() {
        lock.lock();
        try {
            int g = generation;
            nextGeneration();
            broken = g; // cause brokenness setting to stop at previous gen.
            trip.signalAll();
        }
        finally {
            lock.unlock();
        }
    }

    /**
     * Return 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() {
        lock.lock();
        try {
            return parties - count;
        }
        finally {
            lock.unlock();
        }
    }

}


Revision:	1.2
Committed:	Tue May 27 18:14:39 2003 UTC (21 years ago) by dl
Branch:	MAIN
CVS Tags:	JSR166_PRERELEASE_0_1
Changes since 1.1:	+213 -17 lines
Log Message:	re-check-in initial implementations
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain. Use, modify, and
4			* redistribute this code in any way without acknowledgement.
5			*/
6
7	tim	1.1	package java.util.concurrent;
8
9			/**
10			* A <tt>CyclicBarrier</tt> allows a set threads to all wait for each
11			* other to reach a common barrier point. They are useful in programs
12			* involving a fixed sized party of threads that must occasionally
13			* wait for each other. The barrier is <em>cyclic</em> because it can
14			* be re-used after the waiting threads are released.
15			*
16			* <p>A <tt>CyclicBarrier</tt> supports an optional {@link Runnable} command
17			* that is run once per barrier point, after the last thread in the party
18			* arrives, but before any threads are released.
19			* This <em>barrier action</em> is useful
20			* for updating shared-state before any of the parties continue.
21			*
22			* <p><b>Sample usage:</b> Here is a code sketch of
23			* using a barrier in a parallel decomposition design:
24			* <pre>
25			* class Solver {
26			* final int N;
27			* final float[][] data;
28			* final CyclicBarrier barrier;
29			*
30			* class Worker implements Runnable {
31			* int myRow;
32			* Worker(int row) { myRow = row; }
33			* public void run() {
34			* while (!done()) {
35			* processRow(myRow);
36			*
37			* try {
38			* barrier.await();
39			* }
40			* catch (InterruptedException ex) { return; }
41			* catch (BrokenBarrierException ex) { return; }
42			* }
43			* }
44			* }
45			*
46			* public Solver(float[][] matrix) {
47			* data = matrix;
48			* N = matrix.length;
49			* barrier = new CyclicBarrier(N,
50			* new Runnable() {
51			* public void run() {
52			* mergeRows(...);
53			* }
54			* });
55			* for (int i = 0; i < N; ++i)
56			* new Thread(new Worker(i)).start();
57			*
58			* waitUntilDone();
59			* }
60			* }
61			* </pre>
62			* Here, each worker thread processes a row of the matrix then waits at the
63			* barrier until all rows have been processed. When all rows are processed
64			* the supplied {@link Runnable} barrier action is executed and merges the
65			* rows. If the merger
66			* determines that a solution has been found then <tt>done()</tt> will return
67			* <tt>true</tt> and each worker will terminate.
68			*
69			* <p>If the barrier action does not rely on the parties being suspended when
70			* it is executed, then any of the threads in the party could execute that
71			* action when it is released. To facilitate this, each invocation of
72			* {@link #await} returns the arrival index of that thread at the barrier.
73			* You can then choose which thread should execute the barrier action, for
74			* example:
75			* <pre> if (barrier.await() == 0) {
76			* // log the completion of this iteration
77			* }</pre>
78			*
79	dl	1.2	* <p>The <tt>CyclicBarrier</tt> uses an all-or-none breakage model
80			* for failed synchronization attempts: If a thread leaves a barrier
81			* point prematurely because of interruption or timeout, all others
82			* will also leave abnormally (via {@link BrokenBarrierException}),
83			* until the barrier is {@link #reset}. This is usually the simplest
84			* and best strategy for sharing knowledge about failures among
85			* cooperating threads in the most common usage contexts of barriers.
86	tim	1.1	*
87			* <h3>Implementation Considerations</h3>
88			* <p>This implementation has the property that interruptions among newly
89			* arriving threads can cause as-yet-unresumed threads from a previous
90			* barrier cycle to return out as broken. This transmits breakage as
91			* early as possible, but with the possible byproduct that only some
92			* threads returning out of a barrier will realize that it is newly
93			* broken. (Others will not realize this until a future cycle.)
94			*
95			*
96			*
97			* @since 1.5
98			* @spec JSR-166
99	dl	1.2	* @revised $Date: 2003/01/28 06:56:53 $
100			* @editor $Author: dholmes $
101	tim	1.1	*
102			* @fixme Is the above property actually true in this implementation?
103			* @fixme Should we have a timeout version of await()?
104			*/
105			public class CyclicBarrier {
106	dl	1.2	private final ReentrantLock lock = new ReentrantLock();
107			private final Condition trip = lock.newCondition();
108			private final int parties;
109			private Runnable barrierCommand;
110
111			/**
112			* The generation number. Incremented mod Integer.MAX_VALUE every
113			* time barrier tripped. Starts at 1 to simplify handling of
114			* breakage indicator
115			*/
116			private int generation = 1;
117
118			/**
119			* Breakage indicator: last generation of breakage, propagated
120			* across barrier generations until reset.
121			*/
122			private int broken = 0;
123
124			/**
125			* Number of parties still waiting. Counts down from parties to 0
126			* on each cycle.
127			*/
128			private int count;
129
130			/**
131			* Update state on barrier trip.
132			*/
133			private void nextGeneration() {
134			count = parties;
135			int g = generation;
136			// avoid generation == 0
137			if (++generation < 0) generation = 1;
138			// propagate breakage
139			if (broken == g) broken = generation;
140			}
141
142			private int dowait(boolean timed, long nanos) throws InterruptedException, BrokenBarrierException, TimeoutException {
143			lock.lock();
144			try {
145			int index = --count;
146			int g = generation;
147
148			if (broken == g)
149			throw new BrokenBarrierException();
150
151			if (Thread.interrupted()) {
152			broken = g;
153			trip.signalAll();
154			throw new InterruptedException();
155			}
156
157			if (index == 0) { // tripped
158			nextGeneration();
159			trip.signalAll();
160			try {
161			if (barrierCommand != null)
162			barrierCommand.run();
163			return 0;
164			}
165			catch (RuntimeException ex) {
166			broken = generation; // next generation is broken
167			throw ex;
168			}
169			}
170
171			while (generation == g) {
172			try {
173			if (!timed)
174			trip.await();
175			else if (nanos > 0)
176			nanos = trip.awaitNanos(nanos);
177			}
178			catch (InterruptedException ex) {
179			// Only claim that broken if interrupted before reset
180			if (generation == g) {
181			broken = g;
182			trip.signalAll();
183			throw ex;
184			}
185			else {
186			Thread.currentThread().interrupt(); // propagate
187			break;
188			}
189			}
190
191			if (timed && nanos <= 0) {
192			broken = g;
193			trip.signalAll();
194			throw new TimeoutException();
195			}
196
197			if (broken == generation)
198			throw new BrokenBarrierException();
199
200			}
201			return index;
202
203			}
204			finally {
205			lock.unlock();
206			}
207			}
208	tim	1.1
209			/**
210			* Create a new <tt>CyclicBarrier</tt> that will trip when the
211			* given number of parties (threads) are waiting upon it, and which
212			* will execute the given barrier action when the barrier is tripped.
213			*
214			* @param parties the number of threads that must invoke {@link #await}
215			* before the barrier is tripped.
216			* @param barrierAction the command to execute when the barrier is
217			* tripped.
218			*
219			* @throws IllegalArgumentException if <tt>parties</tt> is less than 1.
220			*/
221			public CyclicBarrier(int parties, Runnable barrierAction) {
222	dl	1.2	if (parties <= 0) throw new IllegalArgumentException();
223			this.parties = parties;
224			this.count = parties;
225			this.barrierCommand = barrierAction;
226	tim	1.1	}
227
228			/**
229			* Create a new <tt>CyclicBarrier</tt> that will trip when the
230			* given number of parties (threads) are waiting upon it.
231			*
232			* <p>This is equivalent to <tt>CyclicBarrier(parties, null)</tt>.
233			*
234			* @param parties the number of threads that must invoke {@link #await}
235			* before the barrier is tripped.
236			*
237			* @throws IllegalArgumentException if <tt>parties</tt> is less than 1.
238			*/
239			public CyclicBarrier(int parties) {
240	dl	1.2	this(parties, null);
241	tim	1.1	}
242
243			/**
244			* Return the number of parties required to trip this barrier.
245			* @return the number of parties required to trip this barrier.
246			**/
247			public int getParties() {
248	dl	1.2	return parties;
249	tim	1.1	}
250
251			/**
252			* Wait until all {@link #getParties parties} have invoked <tt>await</tt>
253			* on this barrier.
254			*
255			* <p>If the current thread is not the last to arrive then it is
256			* disabled for thread scheduling purposes and lies dormant until
257	dl	1.2	* one of following things happens:
258	tim	1.1	* <ul>
259			* <li>The last thread arrives; or
260			* <li>Some other thread {@link Thread#interrupt interrupts} the current
261			* thread; or
262			* <li>Some other thread {@link Thread#interrupt interrupts} one of the
263			* other waiting threads; or
264	dl	1.2	* <li>Some other thread times out while waiting for barrier; or
265	tim	1.1	* <li>Some other thread invokes {@link #reset} on this barrier.
266			* </ul>
267			* <p>If the current thread:
268			* <ul>
269			* <li>has its interrupted status set on entry to this method; or
270			* <li>is {@link Thread#interrupt interrupted} while waiting
271			* </ul>
272			* then {@link InterruptedException} is thrown and the current thread's
273			* interrupted status is cleared.
274			*
275			* <p>If the barrier is {@link #reset} while any thread is waiting, or if
276			* the barrier {@link #isBroken is broken} when <tt>await</tt> is invoked
277			* then {@link BrokenBarrierException} is thrown.
278			*
279			* <p>If any thread is {@link Thread#interrupt interrupted} while waiting,
280			* then all other waiting threads will throw
281			* {@link BrokenBarrierException} and the barrier is placed in the broken
282			* state.
283			*
284			* <p>If the current thread is the last thread to arrive, and a
285			* non-null barrier action was supplied in the constructor, then the
286			* current thread runs the action before allowing the other threads to
287			* continue.
288			* If an exception occurs during the barrier action then that exception
289			* will be propagated in the current thread.
290			*
291			* @return the arrival index of the current thread, where index
292			* <tt>{@link #getParties()} - 1</tt> indicates the first to arrive and
293			* zero indicates the last to arrive.
294			*
295			* @throws InterruptedException if the current thread was interrupted
296			* while waiting
297			* @throws BrokenBarrierException if <em>another</em> thread was
298			* interrupted while the current thread was waiting, or the barrier was
299			* reset, or the barrier was broken when <tt>await</tt> was called.
300			*/
301			public int await() throws InterruptedException, BrokenBarrierException {
302	dl	1.2	try {
303			return dowait(false, 0);
304			}
305			catch (TimeoutException toe) {
306			throw new Error(toe); // cannot happen;
307			}
308			}
309
310			/**
311			* Wait until all {@link #getParties parties} have invoked <tt>await</tt>
312			* on this barrier.
313			*
314			* <p>If the current thread is not the last to arrive then it is
315			* disabled for thread scheduling purposes and lies dormant until
316			* one of the following things happens:
317			* <ul>
318			* <li>The last thread arrives; or
319			* <li>The speceified timeout elapses; or
320			* <li>Some other thread {@link Thread#interrupt interrupts} the current
321			* thread; or
322			* <li>Some other thread {@link Thread#interrupt interrupts} one of the
323			* other waiting threads; or
324			* <li>Some other thread times out while waiting for barrier; or
325			* <li>Some other thread invokes {@link #reset} on this barrier.
326			* </ul>
327			* <p>If the current thread:
328			* <ul>
329			* <li>has its interrupted status set on entry to this method; or
330			* <li>is {@link Thread#interrupt interrupted} while waiting
331			* </ul>
332			* then {@link InterruptedException} is thrown and the current thread's
333			* interrupted status is cleared.
334			*
335			* <p>If the barrier is {@link #reset} while any thread is waiting, or if
336			* the barrier {@link #isBroken is broken} when <tt>await</tt> is invoked
337			* then {@link BrokenBarrierException} is thrown.
338			*
339			* <p>If any thread is {@link Thread#interrupt interrupted} while waiting,
340			* then all other waiting threads will throw
341			* {@link BrokenBarrierException} and the barrier is placed in the broken
342			* state.
343			*
344			* <p>If the current thread is the last thread to arrive, and a
345			* non-null barrier action was supplied in the constructor, then the
346			* current thread runs the action before allowing the other threads to
347			* continue.
348			* If an exception occurs during the barrier action then that exception
349			* will be propagated in the current thread.
350			*
351			* @return the arrival index of the current thread, where index
352			* <tt>{@link #getParties()} - 1</tt> indicates the first to arrive and
353			* zero indicates the last to arrive.
354			*
355			* @throws InterruptedException if the current thread was interrupted
356			* while waiting
357			* @throws TimeoutException if the specified timeout elapses.
358			* @throws BrokenBarrierException if <em>another</em> thread was
359			* interrupted while the current thread was waiting, or the barrier was
360			* reset, or the barrier was broken when <tt>await</tt> was called.
361			*/
362			public int await(long timeout, TimeUnit unit) throws InterruptedException, BrokenBarrierException, TimeoutException {
363			return dowait(true, unit.toNanos(timeout));
364	tim	1.1	}
365
366			/**
367			* Query if this barrier is in a broken state.
368			* @return <tt>true</tt> if one or more parties broke out of this
369	dl	1.2	* barrier due to interruption or timeout since construction or
370			* the last reset; and <tt>false</tt> otherwise.
371	tim	1.1	*/
372			public boolean isBroken() {
373	dl	1.2	lock.lock();
374			try {
375			return broken >= generation;
376			}
377			finally {
378			lock.unlock();
379			}
380	tim	1.1	}
381
382			/**
383			* Reset the barrier to its initial state. If any parties are
384			* currently waiting at the barrier, they will return with a
385			* {@link BrokenBarrierException}.
386			*/
387			public void reset() {
388	dl	1.2	lock.lock();
389			try {
390			int g = generation;
391			nextGeneration();
392			broken = g; // cause brokenness setting to stop at previous gen.
393			trip.signalAll();
394			}
395			finally {
396			lock.unlock();
397			}
398	tim	1.1	}
399
400			/**
401			* Return the number of parties currently waiting at the barrier.
402			* This method is primarily useful for debugging and assertions.
403			*
404			* @return the number of parties currently blocked in {@link #await}
405			**/
406			public int getNumberWaiting() {
407	dl	1.2	lock.lock();
408			try {
409			return parties - count;
410			}
411			finally {
412			lock.unlock();
413			}
414	tim	1.1	}
415
416			}
417
418