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;
import java.util.concurrent.locks.*;

/**
 * A synchronization aid that allows a set 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>
 * 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.
 *
 * @since 1.5
 * @spec JSR-166
 * @revised $Date: 2003/08/05 22:50:28 $
 * @editor $Author: dl $
 * @see CountDownLatch
 *
 * @author Doug Lea
 */
public class CyclicBarrier {
    /** 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 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;
    }

    /**
     * Main barrier code, covering the various policies.
     */
    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 == g) 
                    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.
     *
     * @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 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}. Note that resets <em>after</em>
     * a breakage 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() {
        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:	1.8
Committed:	Tue Aug 5 23:59:16 2003 UTC (20 years, 10 months ago) by dl
Branch:	MAIN
CVS Tags:	JSR166_CR1
Changes since 1.7:	+6 -2 lines
Log Message:	Expanded reset docs
#	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	dl	1.6	import java.util.concurrent.locks.*;
9	tim	1.1
10			/**
11	dl	1.3	* A synchronization aid that allows a set threads to all wait for
12	brian	1.4	* each other to reach a common barrier point. CyclicBarriers are
13	dl	1.3	* useful in programs involving a fixed sized party of threads that
14	brian	1.4	* must occasionally wait for each other. The barrier is called
15	dl	1.3	* <em>cyclic</em> because it can be re-used after the waiting threads
16			* are released.
17	tim	1.1	*
18			* <p>A <tt>CyclicBarrier</tt> supports an optional {@link Runnable} command
19			* that is run once per barrier point, after the last thread in the party
20			* arrives, but before any threads are released.
21			* This <em>barrier action</em> is useful
22			* for updating shared-state before any of the parties continue.
23			*
24	brian	1.4	* <p><b>Sample usage:</b> Here is an example of
25	tim	1.1	* using a barrier in a parallel decomposition design:
26			* <pre>
27			* class Solver {
28			* final int N;
29			* final float[][] data;
30			* final CyclicBarrier barrier;
31			*
32			* class Worker implements Runnable {
33			* int myRow;
34			* Worker(int row) { myRow = row; }
35			* public void run() {
36			* while (!done()) {
37			* processRow(myRow);
38			*
39			* try {
40			* barrier.await();
41			* }
42			* catch (InterruptedException ex) { return; }
43			* catch (BrokenBarrierException ex) { return; }
44			* }
45			* }
46			* }
47			*
48			* public Solver(float[][] matrix) {
49			* data = matrix;
50			* N = matrix.length;
51			* barrier = new CyclicBarrier(N,
52			* new Runnable() {
53			* public void run() {
54			* mergeRows(...);
55			* }
56			* });
57			* for (int i = 0; i < N; ++i)
58			* new Thread(new Worker(i)).start();
59			*
60			* waitUntilDone();
61			* }
62			* }
63			* </pre>
64			* Here, each worker thread processes a row of the matrix then waits at the
65			* barrier until all rows have been processed. When all rows are processed
66			* the supplied {@link Runnable} barrier action is executed and merges the
67			* rows. If the merger
68			* determines that a solution has been found then <tt>done()</tt> will return
69			* <tt>true</tt> and each worker will terminate.
70			*
71			* <p>If the barrier action does not rely on the parties being suspended when
72			* it is executed, then any of the threads in the party could execute that
73			* action when it is released. To facilitate this, each invocation of
74			* {@link #await} returns the arrival index of that thread at the barrier.
75			* You can then choose which thread should execute the barrier action, for
76			* example:
77			* <pre> if (barrier.await() == 0) {
78			* // log the completion of this iteration
79			* }</pre>
80			*
81	dl	1.2	* <p>The <tt>CyclicBarrier</tt> uses an all-or-none breakage model
82			* for failed synchronization attempts: If a thread leaves a barrier
83			* point prematurely because of interruption or timeout, all others
84			* will also leave abnormally (via {@link BrokenBarrierException}),
85			* until the barrier is {@link #reset}. This is usually the simplest
86			* and best strategy for sharing knowledge about failures among
87			* cooperating threads in the most common usage contexts of barriers.
88	tim	1.1	*
89			* @since 1.5
90			* @spec JSR-166
91	dl	1.8	* @revised $Date: 2003/08/05 22:50:28 $
92	dl	1.6	* @editor $Author: dl $
93	brian	1.4	* @see CountDownLatch
94	tim	1.1	*
95	dl	1.5	* @author Doug Lea
96	tim	1.1	*/
97			public class CyclicBarrier {
98	dl	1.5	/** The lock for guarding barrier entry */
99	dl	1.2	private final ReentrantLock lock = new ReentrantLock();
100	dl	1.5	/** Condition to wait on until tripped */
101	dl	1.2	private final Condition trip = lock.newCondition();
102	dl	1.5	/** The number of parties */
103	dl	1.2	private final int parties;
104	dl	1.5	/* The command to run when tripped */
105	dl	1.2	private Runnable barrierCommand;
106
107			/**
108			* The generation number. Incremented mod Integer.MAX_VALUE every
109			* time barrier tripped. Starts at 1 to simplify handling of
110			* breakage indicator
111			*/
112			private int generation = 1;
113
114			/**
115			* Breakage indicator: last generation of breakage, propagated
116			* across barrier generations until reset.
117			*/
118			private int broken = 0;
119
120			/**
121			* Number of parties still waiting. Counts down from parties to 0
122			* on each cycle.
123			*/
124			private int count;
125
126			/**
127			* Update state on barrier trip.
128			*/
129			private void nextGeneration() {
130			count = parties;
131			int g = generation;
132			// avoid generation == 0
133			if (++generation < 0) generation = 1;
134			// propagate breakage
135			if (broken == g) broken = generation;
136			}
137
138	dl	1.5	/**
139	dl	1.7	* Main barrier code, covering the various policies.
140	dl	1.5	*/
141	dl	1.2	private int dowait(boolean timed, long nanos) throws InterruptedException, BrokenBarrierException, TimeoutException {
142			lock.lock();
143			try {
144			int index = --count;
145			int g = generation;
146
147			if (broken == g)
148			throw new BrokenBarrierException();
149
150			if (Thread.interrupted()) {
151			broken = g;
152			trip.signalAll();
153			throw new InterruptedException();
154			}
155
156			if (index == 0) { // tripped
157			nextGeneration();
158			trip.signalAll();
159			try {
160			if (barrierCommand != null)
161			barrierCommand.run();
162			return 0;
163			}
164			catch (RuntimeException ex) {
165			broken = generation; // next generation is broken
166			throw ex;
167			}
168			}
169
170			while (generation == g) {
171			try {
172			if (!timed)
173			trip.await();
174			else if (nanos > 0)
175			nanos = trip.awaitNanos(nanos);
176			}
177			catch (InterruptedException ex) {
178			// Only claim that broken if interrupted before reset
179			if (generation == g) {
180			broken = g;
181			trip.signalAll();
182			throw ex;
183			}
184			else {
185			Thread.currentThread().interrupt(); // propagate
186			break;
187			}
188			}
189
190			if (timed && nanos <= 0) {
191			broken = g;
192			trip.signalAll();
193			throw new TimeoutException();
194			}
195
196	dl	1.7	if (broken == g)
197	dl	1.2	throw new BrokenBarrierException();
198
199			}
200			return index;
201
202			}
203			finally {
204			lock.unlock();
205			}
206			}
207	tim	1.1
208			/**
209			* Create a new <tt>CyclicBarrier</tt> that will trip when the
210			* given number of parties (threads) are waiting upon it, and which
211			* will execute the given barrier action when the barrier is tripped.
212			*
213			* @param parties the number of threads that must invoke {@link #await}
214			* before the barrier is tripped.
215			* @param barrierAction the command to execute when the barrier is
216			* tripped.
217			*
218			* @throws IllegalArgumentException if <tt>parties</tt> is less than 1.
219			*/
220			public CyclicBarrier(int parties, Runnable barrierAction) {
221	dl	1.2	if (parties <= 0) throw new IllegalArgumentException();
222			this.parties = parties;
223			this.count = parties;
224			this.barrierCommand = barrierAction;
225	tim	1.1	}
226
227			/**
228			* Create a new <tt>CyclicBarrier</tt> that will trip when the
229			* given number of parties (threads) are waiting upon it.
230			*
231			* <p>This is equivalent to <tt>CyclicBarrier(parties, null)</tt>.
232			*
233			* @param parties the number of threads that must invoke {@link #await}
234			* before the barrier is tripped.
235			*
236			* @throws IllegalArgumentException if <tt>parties</tt> is less than 1.
237			*/
238			public CyclicBarrier(int parties) {
239	dl	1.2	this(parties, null);
240	tim	1.1	}
241
242			/**
243			* Return the number of parties required to trip this barrier.
244			* @return the number of parties required to trip this barrier.
245			**/
246			public int getParties() {
247	dl	1.2	return parties;
248	tim	1.1	}
249
250			/**
251			* Wait until all {@link #getParties parties} have invoked <tt>await</tt>
252			* on this barrier.
253			*
254			* <p>If the current thread is not the last to arrive then it is
255			* disabled for thread scheduling purposes and lies dormant until
256	dl	1.2	* one of following things happens:
257	tim	1.1	* <ul>
258			* <li>The last thread arrives; or
259			* <li>Some other thread {@link Thread#interrupt interrupts} the current
260			* thread; or
261			* <li>Some other thread {@link Thread#interrupt interrupts} one of the
262			* other waiting threads; or
263	dl	1.2	* <li>Some other thread times out while waiting for barrier; or
264	tim	1.1	* <li>Some other thread invokes {@link #reset} on this barrier.
265			* </ul>
266			* <p>If the current thread:
267			* <ul>
268			* <li>has its interrupted status set on entry to this method; or
269			* <li>is {@link Thread#interrupt interrupted} while waiting
270			* </ul>
271			* then {@link InterruptedException} is thrown and the current thread's
272			* interrupted status is cleared.
273			*
274			* <p>If the barrier is {@link #reset} while any thread is waiting, or if
275			* the barrier {@link #isBroken is broken} when <tt>await</tt> is invoked
276			* then {@link BrokenBarrierException} is thrown.
277			*
278			* <p>If any thread is {@link Thread#interrupt interrupted} while waiting,
279			* then all other waiting threads will throw
280			* {@link BrokenBarrierException} and the barrier is placed in the broken
281			* state.
282			*
283			* <p>If the current thread is the last thread to arrive, and a
284			* non-null barrier action was supplied in the constructor, then the
285			* current thread runs the action before allowing the other threads to
286			* continue.
287			* If an exception occurs during the barrier action then that exception
288			* will be propagated in the current thread.
289			*
290			* @return the arrival index of the current thread, where index
291			* <tt>{@link #getParties()} - 1</tt> indicates the first to arrive and
292			* zero indicates the last to arrive.
293			*
294			* @throws InterruptedException if the current thread was interrupted
295			* while waiting
296			* @throws BrokenBarrierException if <em>another</em> thread was
297			* interrupted while the current thread was waiting, or the barrier was
298			* reset, or the barrier was broken when <tt>await</tt> was called.
299			*/
300			public int await() throws InterruptedException, BrokenBarrierException {
301	dl	1.2	try {
302			return dowait(false, 0);
303			}
304			catch (TimeoutException toe) {
305			throw new Error(toe); // cannot happen;
306			}
307			}
308
309			/**
310			* Wait until all {@link #getParties parties} have invoked <tt>await</tt>
311			* on this barrier.
312			*
313			* <p>If the current thread is not the last to arrive then it is
314			* disabled for thread scheduling purposes and lies dormant until
315			* one of the following things happens:
316			* <ul>
317			* <li>The last thread arrives; or
318			* <li>The speceified timeout elapses; or
319			* <li>Some other thread {@link Thread#interrupt interrupts} the current
320			* thread; or
321			* <li>Some other thread {@link Thread#interrupt interrupts} one of the
322			* other waiting threads; or
323			* <li>Some other thread times out while waiting for barrier; or
324			* <li>Some other thread invokes {@link #reset} on this barrier.
325			* </ul>
326			* <p>If the current thread:
327			* <ul>
328			* <li>has its interrupted status set on entry to this method; or
329			* <li>is {@link Thread#interrupt interrupted} while waiting
330			* </ul>
331			* then {@link InterruptedException} is thrown and the current thread's
332			* interrupted status is cleared.
333			*
334			* <p>If the barrier is {@link #reset} while any thread is waiting, or if
335			* the barrier {@link #isBroken is broken} when <tt>await</tt> is invoked
336			* then {@link BrokenBarrierException} is thrown.
337			*
338			* <p>If any thread is {@link Thread#interrupt interrupted} while waiting,
339			* then all other waiting threads will throw
340			* {@link BrokenBarrierException} and the barrier is placed in the broken
341			* state.
342			*
343			* <p>If the current thread is the last thread to arrive, and a
344			* non-null barrier action was supplied in the constructor, then the
345			* current thread runs the action before allowing the other threads to
346			* continue.
347			* If an exception occurs during the barrier action then that exception
348			* will be propagated in the current thread.
349			*
350	dl	1.5	* @param timeout the time to wait for the barrier
351			* @param unit the time unit of the timeout parameter
352	dl	1.2	* @return the arrival index of the current thread, where index
353			* <tt>{@link #getParties()} - 1</tt> indicates the first to arrive and
354			* zero indicates the last to arrive.
355			*
356			* @throws InterruptedException if the current thread was interrupted
357			* while waiting
358			* @throws TimeoutException if the specified timeout elapses.
359			* @throws BrokenBarrierException if <em>another</em> thread was
360			* interrupted while the current thread was waiting, or the barrier was
361			* reset, or the barrier was broken when <tt>await</tt> was called.
362			*/
363			public int await(long timeout, TimeUnit unit) throws InterruptedException, BrokenBarrierException, TimeoutException {
364			return dowait(true, unit.toNanos(timeout));
365	tim	1.1	}
366
367			/**
368			* Query if this barrier is in a broken state.
369			* @return <tt>true</tt> if one or more parties broke out of this
370	dl	1.2	* barrier due to interruption or timeout since construction or
371			* the last reset; and <tt>false</tt> otherwise.
372	tim	1.1	*/
373			public boolean isBroken() {
374	dl	1.2	lock.lock();
375			try {
376			return broken >= generation;
377			}
378			finally {
379			lock.unlock();
380			}
381	tim	1.1	}
382
383			/**
384			* Reset the barrier to its initial state. If any parties are
385			* currently waiting at the barrier, they will return with a
386	dl	1.8	* {@link BrokenBarrierException}. Note that resets <em>after</em>
387			* a breakage can be complicated to carry out; threads need to
388			* re-synchronize in some other way, and choose one to perform the
389			* reset. It may be preferable to instead create a new barrier
390			* for subsequent use.
391	tim	1.1	*/
392			public void reset() {
393	dl	1.2	lock.lock();
394			try {
395			int g = generation;
396			nextGeneration();
397			broken = g; // cause brokenness setting to stop at previous gen.
398			trip.signalAll();
399			}
400			finally {
401			lock.unlock();
402			}
403	tim	1.1	}
404
405			/**
406			* Return the number of parties currently waiting at the barrier.
407			* This method is primarily useful for debugging and assertions.
408			*
409			* @return the number of parties currently blocked in {@link #await}
410			**/
411			public int getNumberWaiting() {
412	dl	1.2	lock.lock();
413			try {
414			return parties - count;
415			}
416			finally {
417			lock.unlock();
418			}
419	tim	1.1	}
420
421			}
422
423