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 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>
 * 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: 2003/08/23 19:47:29 $
 * @editor $Author: tim $
 * @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;
                }
                catch (Error 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:	1.11
Committed:	Mon Aug 25 22:32:40 2003 UTC (20 years, 9 months ago) by dholmes
Branch:	MAIN
Changes since 1.10:	+11 -5 lines
Log Message:	Added missing "catch (Error ex)" clause in dowAwait after running barrier action. Minor formatting changes.
#	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	tim	1.10	* A synchronization aid that allows a set of 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	tim	1.9	* } catch (InterruptedException ex) {
42			* return;
43			* } catch (BrokenBarrierException ex) {
44			* return;
45	tim	1.1	* }
46			* }
47			* }
48			* }
49			*
50			* public Solver(float[][] matrix) {
51			* data = matrix;
52			* N = matrix.length;
53			* barrier = new CyclicBarrier(N,
54			* new Runnable() {
55			* public void run() {
56			* mergeRows(...);
57			* }
58			* });
59			* for (int i = 0; i < N; ++i)
60			* new Thread(new Worker(i)).start();
61			*
62			* waitUntilDone();
63			* }
64			* }
65			* </pre>
66			* Here, each worker thread processes a row of the matrix then waits at the
67			* barrier until all rows have been processed. When all rows are processed
68			* the supplied {@link Runnable} barrier action is executed and merges the
69			* rows. If the merger
70			* determines that a solution has been found then <tt>done()</tt> will return
71			* <tt>true</tt> and each worker will terminate.
72			*
73			* <p>If the barrier action does not rely on the parties being suspended when
74			* it is executed, then any of the threads in the party could execute that
75			* action when it is released. To facilitate this, each invocation of
76			* {@link #await} returns the arrival index of that thread at the barrier.
77			* You can then choose which thread should execute the barrier action, for
78			* example:
79			* <pre> if (barrier.await() == 0) {
80			* // log the completion of this iteration
81			* }</pre>
82			*
83	dl	1.2	* <p>The <tt>CyclicBarrier</tt> uses an all-or-none breakage model
84			* for failed synchronization attempts: If a thread leaves a barrier
85			* point prematurely because of interruption or timeout, all others
86			* will also leave abnormally (via {@link BrokenBarrierException}),
87			* until the barrier is {@link #reset}. This is usually the simplest
88			* and best strategy for sharing knowledge about failures among
89			* cooperating threads in the most common usage contexts of barriers.
90	tim	1.1	*
91			* @since 1.5
92			* @spec JSR-166
93	dholmes	1.11	* @revised $Date: 2003/08/23 19:47:29 $
94	tim	1.10	* @editor $Author: tim $
95	brian	1.4	* @see CountDownLatch
96	tim	1.1	*
97	dl	1.5	* @author Doug Lea
98	tim	1.1	*/
99			public class CyclicBarrier {
100	dl	1.5	/** The lock for guarding barrier entry */
101	dl	1.2	private final ReentrantLock lock = new ReentrantLock();
102	dl	1.5	/** Condition to wait on until tripped */
103	dl	1.2	private final Condition trip = lock.newCondition();
104	dl	1.5	/** The number of parties */
105	dl	1.2	private final int parties;
106	dl	1.5	/* The command to run when tripped */
107	dl	1.2	private Runnable barrierCommand;
108
109			/**
110			* The generation number. Incremented mod Integer.MAX_VALUE every
111			* time barrier tripped. Starts at 1 to simplify handling of
112			* breakage indicator
113			*/
114			private int generation = 1;
115
116			/**
117			* Breakage indicator: last generation of breakage, propagated
118			* across barrier generations until reset.
119			*/
120			private int broken = 0;
121
122			/**
123			* Number of parties still waiting. Counts down from parties to 0
124			* on each cycle.
125			*/
126			private int count;
127
128			/**
129			* Update state on barrier trip.
130			*/
131			private void nextGeneration() {
132			count = parties;
133			int g = generation;
134			// avoid generation == 0
135			if (++generation < 0) generation = 1;
136			// propagate breakage
137			if (broken == g) broken = generation;
138			}
139
140	dl	1.5	/**
141	dl	1.7	* Main barrier code, covering the various policies.
142	dl	1.5	*/
143	dholmes	1.11	private int dowait(boolean timed, long nanos)
144			throws InterruptedException, BrokenBarrierException, TimeoutException {
145	dl	1.2	lock.lock();
146			try {
147			int index = --count;
148			int g = generation;
149
150			if (broken == g)
151			throw new BrokenBarrierException();
152
153			if (Thread.interrupted()) {
154			broken = g;
155			trip.signalAll();
156			throw new InterruptedException();
157			}
158
159			if (index == 0) { // tripped
160			nextGeneration();
161			trip.signalAll();
162			try {
163			if (barrierCommand != null)
164			barrierCommand.run();
165			return 0;
166	tim	1.9	} catch (RuntimeException ex) {
167	dl	1.2	broken = generation; // next generation is broken
168			throw ex;
169			}
170	dholmes	1.11	catch (Error ex) {
171			broken = generation; // next generation is broken
172			throw ex;
173			}
174	dl	1.2	}
175
176			while (generation == g) {
177			try {
178			if (!timed)
179			trip.await();
180			else if (nanos > 0)
181			nanos = trip.awaitNanos(nanos);
182	tim	1.9	} catch (InterruptedException ex) {
183	dl	1.2	// Only claim that broken if interrupted before reset
184			if (generation == g) {
185			broken = g;
186			trip.signalAll();
187			throw ex;
188	tim	1.9	} else {
189	dl	1.2	Thread.currentThread().interrupt(); // propagate
190			break;
191			}
192			}
193
194			if (timed && nanos <= 0) {
195			broken = g;
196			trip.signalAll();
197			throw new TimeoutException();
198			}
199
200	dl	1.7	if (broken == g)
201	dl	1.2	throw new BrokenBarrierException();
202
203			}
204			return index;
205
206	tim	1.9	} finally {
207	dl	1.2	lock.unlock();
208			}
209			}
210	tim	1.1
211			/**
212			* Create a new <tt>CyclicBarrier</tt> that will trip when the
213			* given number of parties (threads) are waiting upon it, and which
214			* will execute the given barrier action when the barrier is tripped.
215			*
216			* @param parties the number of threads that must invoke {@link #await}
217			* before the barrier is tripped.
218			* @param barrierAction the command to execute when the barrier is
219			* tripped.
220			*
221			* @throws IllegalArgumentException if <tt>parties</tt> is less than 1.
222			*/
223			public CyclicBarrier(int parties, Runnable barrierAction) {
224	dl	1.2	if (parties <= 0) throw new IllegalArgumentException();
225			this.parties = parties;
226			this.count = parties;
227			this.barrierCommand = barrierAction;
228	tim	1.1	}
229
230			/**
231			* Create a new <tt>CyclicBarrier</tt> that will trip when the
232			* given number of parties (threads) are waiting upon it.
233			*
234			* <p>This is equivalent to <tt>CyclicBarrier(parties, null)</tt>.
235			*
236			* @param parties the number of threads that must invoke {@link #await}
237			* before the barrier is tripped.
238			*
239			* @throws IllegalArgumentException if <tt>parties</tt> is less than 1.
240			*/
241			public CyclicBarrier(int parties) {
242	dl	1.2	this(parties, null);
243	tim	1.1	}
244
245			/**
246			* Return the number of parties required to trip this barrier.
247			* @return the number of parties required to trip this barrier.
248			**/
249			public int getParties() {
250	dl	1.2	return parties;
251	tim	1.1	}
252
253			/**
254			* Wait until all {@link #getParties parties} have invoked <tt>await</tt>
255			* on this barrier.
256			*
257			* <p>If the current thread is not the last to arrive then it is
258			* disabled for thread scheduling purposes and lies dormant until
259	dl	1.2	* one of following things happens:
260	tim	1.1	* <ul>
261			* <li>The last thread arrives; or
262			* <li>Some other thread {@link Thread#interrupt interrupts} the current
263			* thread; or
264			* <li>Some other thread {@link Thread#interrupt interrupts} one of the
265			* other waiting threads; or
266	dl	1.2	* <li>Some other thread times out while waiting for barrier; or
267	tim	1.1	* <li>Some other thread invokes {@link #reset} on this barrier.
268			* </ul>
269			* <p>If the current thread:
270			* <ul>
271			* <li>has its interrupted status set on entry to this method; or
272			* <li>is {@link Thread#interrupt interrupted} while waiting
273			* </ul>
274			* then {@link InterruptedException} is thrown and the current thread's
275			* interrupted status is cleared.
276			*
277			* <p>If the barrier is {@link #reset} while any thread is waiting, or if
278			* the barrier {@link #isBroken is broken} when <tt>await</tt> is invoked
279			* then {@link BrokenBarrierException} is thrown.
280			*
281			* <p>If any thread is {@link Thread#interrupt interrupted} while waiting,
282			* then all other waiting threads will throw
283			* {@link BrokenBarrierException} and the barrier is placed in the broken
284			* state.
285			*
286			* <p>If the current thread is the last thread to arrive, and a
287			* non-null barrier action was supplied in the constructor, then the
288			* current thread runs the action before allowing the other threads to
289			* continue.
290			* If an exception occurs during the barrier action then that exception
291			* will be propagated in the current thread.
292			*
293			* @return the arrival index of the current thread, where index
294			* <tt>{@link #getParties()} - 1</tt> indicates the first to arrive and
295			* zero indicates the last to arrive.
296			*
297			* @throws InterruptedException if the current thread was interrupted
298			* while waiting
299			* @throws BrokenBarrierException if <em>another</em> thread was
300			* interrupted while the current thread was waiting, or the barrier was
301			* reset, or the barrier was broken when <tt>await</tt> was called.
302			*/
303			public int await() throws InterruptedException, BrokenBarrierException {
304	dl	1.2	try {
305			return dowait(false, 0);
306	tim	1.9	} catch (TimeoutException toe) {
307	dl	1.2	throw new Error(toe); // cannot happen;
308			}
309			}
310
311			/**
312			* Wait until all {@link #getParties parties} have invoked <tt>await</tt>
313			* on this barrier.
314			*
315			* <p>If the current thread is not the last to arrive then it is
316			* disabled for thread scheduling purposes and lies dormant until
317			* one of the following things happens:
318			* <ul>
319			* <li>The last thread arrives; or
320			* <li>The speceified timeout elapses; or
321			* <li>Some other thread {@link Thread#interrupt interrupts} the current
322			* thread; or
323			* <li>Some other thread {@link Thread#interrupt interrupts} one of the
324			* other waiting threads; or
325			* <li>Some other thread times out while waiting for barrier; or
326			* <li>Some other thread invokes {@link #reset} on this barrier.
327			* </ul>
328			* <p>If the current thread:
329			* <ul>
330			* <li>has its interrupted status set on entry to this method; or
331			* <li>is {@link Thread#interrupt interrupted} while waiting
332			* </ul>
333			* then {@link InterruptedException} is thrown and the current thread's
334			* interrupted status is cleared.
335			*
336			* <p>If the barrier is {@link #reset} while any thread is waiting, or if
337			* the barrier {@link #isBroken is broken} when <tt>await</tt> is invoked
338			* then {@link BrokenBarrierException} is thrown.
339			*
340			* <p>If any thread is {@link Thread#interrupt interrupted} while waiting,
341			* then all other waiting threads will throw
342			* {@link BrokenBarrierException} and the barrier is placed in the broken
343			* state.
344			*
345			* <p>If the current thread is the last thread to arrive, and a
346			* non-null barrier action was supplied in the constructor, then the
347			* current thread runs the action before allowing the other threads to
348			* continue.
349			* If an exception occurs during the barrier action then that exception
350			* will be propagated in the current thread.
351			*
352	dl	1.5	* @param timeout the time to wait for the barrier
353			* @param unit the time unit of the timeout parameter
354	dl	1.2	* @return the arrival index of the current thread, where index
355			* <tt>{@link #getParties()} - 1</tt> indicates the first to arrive and
356			* zero indicates the last to arrive.
357			*
358			* @throws InterruptedException if the current thread was interrupted
359			* while waiting
360			* @throws TimeoutException if the specified timeout elapses.
361			* @throws BrokenBarrierException if <em>another</em> thread was
362			* interrupted while the current thread was waiting, or the barrier was
363			* reset, or the barrier was broken when <tt>await</tt> was called.
364			*/
365	dholmes	1.11	public int await(long timeout, TimeUnit unit)
366			throws InterruptedException,
367			BrokenBarrierException,
368			TimeoutException {
369	dl	1.2	return dowait(true, unit.toNanos(timeout));
370	tim	1.1	}
371
372			/**
373			* Query if this barrier is in a broken state.
374			* @return <tt>true</tt> if one or more parties broke out of this
375	dl	1.2	* barrier due to interruption or timeout since construction or
376			* the last reset; and <tt>false</tt> otherwise.
377	tim	1.1	*/
378			public boolean isBroken() {
379	dl	1.2	lock.lock();
380			try {
381			return broken >= generation;
382	tim	1.9	} finally {
383	dl	1.2	lock.unlock();
384			}
385	tim	1.1	}
386
387			/**
388			* Reset the barrier to its initial state. If any parties are
389			* currently waiting at the barrier, they will return with a
390	dl	1.8	* {@link BrokenBarrierException}. Note that resets <em>after</em>
391			* a breakage can be complicated to carry out; threads need to
392			* re-synchronize in some other way, and choose one to perform the
393			* reset. It may be preferable to instead create a new barrier
394			* for subsequent use.
395	tim	1.1	*/
396			public void reset() {
397	dl	1.2	lock.lock();
398			try {
399			int g = generation;
400			nextGeneration();
401			broken = g; // cause brokenness setting to stop at previous gen.
402			trip.signalAll();
403	tim	1.9	} finally {
404	dl	1.2	lock.unlock();
405			}
406	tim	1.1	}
407
408			/**
409			* Return the number of parties currently waiting at the barrier.
410			* This method is primarily useful for debugging and assertions.
411			*
412			* @return the number of parties currently blocked in {@link #await}
413			**/
414			public int getNumberWaiting() {
415	dl	1.2	lock.lock();
416			try {
417			return parties - count;
418	tim	1.9	} finally {
419	dl	1.2	lock.unlock();
420			}
421	tim	1.1	}
422
423			}