util/concurrent/CyclicBarrier.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/licenses/publicdomain
 */

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, failure, or timeout, all
 * other threads waiting at that barrier point will also leave
 * abnormally via {@link BrokenBarrierException} (or
 * {@link InterruptedException} if they too were interrupted at about
 * the same time).
 *
 * <p>Memory consistency effects: Actions in a thread prior to calling
 * {@code await()}
 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * actions that are part of the barrier action, which in turn
 * <i>happen-before</i> actions following a successful return from the
 * corresponding {@code await()} in other threads.
 *
 * @since 1.5
 * @see CountDownLatch
 *
 * @author Doug Lea
 */
public class CyclicBarrier {
    /**
     * Each use of the barrier is represented as a generation instance.
     * The generation changes whenever the barrier is tripped, or
     * is reset. There can be many generations associated with threads
     * using the barrier - due to the non-deterministic way the lock
     * may be allocated to waiting threads - but only one of these
     * can be active at a time (the one to which <tt>count</tt> applies)
     * and all the rest are either broken or tripped.
     * There need not be an active generation if there has been a break
     * but no subsequent reset.
     */
    private static class Generation {
        boolean broken = false;
    }

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

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

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

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

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

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

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

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

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

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

                if (g != generation)
                    return index;

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

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

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

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

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

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

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

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

    /**
     * Returns the number of parties currently waiting at the barrier.
     * This method is primarily useful for debugging and assertions.
     *
     * @return the number of parties currently blocked in {@link #await}
     */
    public int getNumberWaiting() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return parties - count;
        } finally {
            lock.unlock();
        }
    }
}
Revision:	1.38
Committed:	Sun May 18 23:47:56 2008 UTC (16 years ago) by jsr166
Branch:	MAIN
Changes since 1.37:	+9 -9 lines
Log Message:	Sync with OpenJDK; untabify
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3	dl	1.22	* Expert Group and released to the public domain, as explained at
4			* http://creativecommons.org/licenses/publicdomain
5	dl	1.2	*/
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	dl	1.28	* arrives, but before any threads are released.
21	tim	1.1	* This <em>barrier action</em> is useful
22			* for updating shared-state before any of the parties continue.
23	dl	1.28	*
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	dl	1.28	*
32	tim	1.1	* 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	dl	1.28	* barrier.await();
41			* } 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	dl	1.28	* barrier = new CyclicBarrier(N,
54	tim	1.1	* new Runnable() {
55	dl	1.28	* public void run() {
56			* mergeRows(...);
57	tim	1.1	* }
58			* });
59	dl	1.28	* for (int i = 0; i < N; ++i)
60	tim	1.1	* new Thread(new Worker(i)).start();
61			*
62			* waitUntilDone();
63			* }
64			* }
65			* </pre>
66	dl	1.28	* Here, each worker thread processes a row of the matrix then waits at the
67	tim	1.1	* barrier until all rows have been processed. When all rows are processed
68	dl	1.28	* the supplied {@link Runnable} barrier action is executed and merges the
69	tim	1.1	* 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	dl	1.28	* You can then choose which thread should execute the barrier action, for
78	tim	1.1	* example:
79			* <pre> if (barrier.await() == 0) {
80			* // log the completion of this iteration
81			* }</pre>
82			*
83	dl	1.28	* <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, failure, or timeout, all
86			* other threads waiting at that barrier point will also leave
87			* abnormally via {@link BrokenBarrierException} (or
88	dl	1.31	* {@link InterruptedException} if they too were interrupted at about
89	dl	1.28	* the same time).
90	tim	1.1	*
91	jsr166	1.35	* <p>Memory consistency effects: Actions in a thread prior to calling
92			* {@code await()}
93			* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
94	brian	1.33	* actions that are part of the barrier action, which in turn
95	jsr166	1.35	* <i>happen-before</i> actions following a successful return from the
96			* corresponding {@code await()} in other threads.
97	brian	1.33	*
98	tim	1.1	* @since 1.5
99	brian	1.4	* @see CountDownLatch
100	tim	1.1	*
101	dl	1.5	* @author Doug Lea
102	tim	1.1	*/
103			public class CyclicBarrier {
104	dl	1.28	/**
105			* Each use of the barrier is represented as a generation instance.
106			* The generation changes whenever the barrier is tripped, or
107			* is reset. There can be many generations associated with threads
108			* using the barrier - due to the non-deterministic way the lock
109			* may be allocated to waiting threads - but only one of these
110			* can be active at a time (the one to which <tt>count</tt> applies)
111			* and all the rest are either broken or tripped.
112			* There need not be an active generation if there has been a break
113			* but no subsequent reset.
114			*/
115			private static class Generation {
116			boolean broken = false;
117			}
118
119	dl	1.5	/** The lock for guarding barrier entry */
120	dl	1.2	private final ReentrantLock lock = new ReentrantLock();
121	dl	1.5	/** Condition to wait on until tripped */
122	dl	1.21	private final Condition trip = lock.newCondition();
123	dl	1.5	/** The number of parties */
124	dl	1.2	private final int parties;
125	dl	1.5	/* The command to run when tripped */
126	dl	1.12	private final Runnable barrierCommand;
127	dl	1.28	/** The current generation */
128			private Generation generation = new Generation();
129	dl	1.2
130			/**
131			* Number of parties still waiting. Counts down from parties to 0
132	dl	1.31	* on each generation. It is reset to parties on each new
133			* generation or when broken.
134	dl	1.2	*/
135	dl	1.28	private int count;
136	dl	1.2
137			/**
138	jsr166	1.29	* Updates state on barrier trip and wakes up everyone.
139	dl	1.28	* Called only while holding lock.
140			*/
141	dl	1.2	private void nextGeneration() {
142	dl	1.28	// signal completion of last generation
143			trip.signalAll();
144			// set up next generation
145	dl	1.2	count = parties;
146	dl	1.28	generation = new Generation();
147	dl	1.12	}
148
149			/**
150	jsr166	1.29	* Sets current barrier generation as broken and wakes up everyone.
151	dl	1.28	* Called only while holding lock.
152	dl	1.12	*/
153			private void breakBarrier() {
154	dl	1.28	generation.broken = true;
155	jsr166	1.38	count = parties;
156	dl	1.12	trip.signalAll();
157	dl	1.2	}
158
159	dl	1.5	/**
160	dl	1.7	* Main barrier code, covering the various policies.
161	dl	1.5	*/
162	dl	1.28	private int dowait(boolean timed, long nanos)
163			throws InterruptedException, BrokenBarrierException,
164			TimeoutException {
165	dl	1.20	final ReentrantLock lock = this.lock;
166	dl	1.2	lock.lock();
167			try {
168	dl	1.30	final Generation g = generation;
169	dl	1.2
170	dl	1.28	if (g.broken)
171	dl	1.2	throw new BrokenBarrierException();
172
173			if (Thread.interrupted()) {
174	dl	1.12	breakBarrier();
175	dl	1.2	throw new InterruptedException();
176			}
177
178	dl	1.30	int index = --count;
179			if (index == 0) { // tripped
180			boolean ranAction = false;
181			try {
182	jsr166	1.38	final Runnable command = barrierCommand;
183	dl	1.31	if (command != null)
184			command.run();
185	dl	1.30	ranAction = true;
186			nextGeneration();
187			return 0;
188			} finally {
189			if (!ranAction)
190			breakBarrier();
191			}
192			}
193	dl	1.2
194	dl	1.28	// loop until tripped, broken, interrupted, or timed out
195	dl	1.12	for (;;) {
196	dl	1.2	try {
197	dl	1.28	if (!timed)
198	dl	1.2	trip.await();
199	dl	1.23	else if (nanos > 0L)
200	dl	1.2	nanos = trip.awaitNanos(nanos);
201	dl	1.12	} catch (InterruptedException ie) {
202	jsr166	1.36	if (g == generation && ! g.broken) {
203			breakBarrier();
204	jsr166	1.38	throw ie;
205			} else {
206			// We're about to finish waiting even if we had not
207			// been interrupted, so this interrupt is deemed to
208			// "belong" to subsequent execution.
209			Thread.currentThread().interrupt();
210			}
211	dl	1.2	}
212	dl	1.28
213	dl	1.30	if (g.broken)
214	dl	1.12	throw new BrokenBarrierException();
215
216	jsr166	1.36	if (g != generation)
217	dl	1.12	return index;
218
219	dl	1.23	if (timed && nanos <= 0L) {
220	dl	1.12	breakBarrier();
221	dl	1.2	throw new TimeoutException();
222			}
223			}
224	tim	1.9	} finally {
225	dl	1.2	lock.unlock();
226			}
227			}
228	tim	1.1
229			/**
230	dl	1.25	* Creates a new <tt>CyclicBarrier</tt> that will trip when the
231	tim	1.1	* given number of parties (threads) are waiting upon it, and which
232	dl	1.17	* will execute the given barrier action when the barrier is tripped,
233	dl	1.19	* performed by the last thread entering the barrier.
234	tim	1.1	*
235			* @param parties the number of threads that must invoke {@link #await}
236	jsr166	1.37	* before the barrier is tripped
237	tim	1.1	* @param barrierAction the command to execute when the barrier is
238	jsr166	1.37	* tripped, or {@code null} if there is no action
239			* @throws IllegalArgumentException if {@code parties} is less than 1
240	tim	1.1	*/
241			public CyclicBarrier(int parties, Runnable barrierAction) {
242	dl	1.2	if (parties <= 0) throw new IllegalArgumentException();
243	dl	1.28	this.parties = parties;
244	dl	1.2	this.count = parties;
245			this.barrierCommand = barrierAction;
246	tim	1.1	}
247
248			/**
249	dl	1.25	* Creates a new <tt>CyclicBarrier</tt> that will trip when the
250	dl	1.14	* given number of parties (threads) are waiting upon it, and
251	dl	1.31	* does not perform a predefined action when the barrier is tripped.
252	tim	1.1	*
253			* @param parties the number of threads that must invoke {@link #await}
254	jsr166	1.37	* before the barrier is tripped
255			* @throws IllegalArgumentException if {@code parties} is less than 1
256	tim	1.1	*/
257			public CyclicBarrier(int parties) {
258	dl	1.2	this(parties, null);
259	tim	1.1	}
260
261			/**
262	dl	1.25	* Returns the number of parties required to trip this barrier.
263	jsr166	1.37	*
264			* @return the number of parties required to trip this barrier
265	dl	1.31	*/
266	tim	1.1	public int getParties() {
267	dl	1.2	return parties;
268	tim	1.1	}
269
270			/**
271	jsr166	1.37	* Waits until all {@linkplain #getParties parties} have invoked
272			* <tt>await</tt> on this barrier.
273	tim	1.1	*
274			* <p>If the current thread is not the last to arrive then it is
275			* disabled for thread scheduling purposes and lies dormant until
276	jsr166	1.36	* one of the following things happens:
277	tim	1.1	* <ul>
278			* <li>The last thread arrives; or
279	jsr166	1.37	* <li>Some other thread {@linkplain Thread#interrupt interrupts}
280			* the current thread; or
281			* <li>Some other thread {@linkplain Thread#interrupt interrupts}
282			* one of the other waiting threads; or
283	dl	1.24	* <li>Some other thread times out while waiting for barrier; or
284	tim	1.1	* <li>Some other thread invokes {@link #reset} on this barrier.
285			* </ul>
286	jsr166	1.37	*
287	tim	1.1	* <p>If the current thread:
288			* <ul>
289			* <li>has its interrupted status set on entry to this method; or
290	jsr166	1.37	* <li>is {@linkplain Thread#interrupt interrupted} while waiting
291	tim	1.1	* </ul>
292			* then {@link InterruptedException} is thrown and the current thread's
293			* interrupted status is cleared.
294			*
295	jsr166	1.37	* <p>If the barrier is {@link #reset} while any thread is waiting,
296			* or if the barrier {@linkplain #isBroken is broken} when
297			* <tt>await</tt> is invoked, or while any thread is waiting, then
298			* {@link BrokenBarrierException} is thrown.
299	tim	1.1	*
300	jsr166	1.37	* <p>If any thread is {@linkplain Thread#interrupt interrupted} while waiting,
301	dl	1.28	* then all other waiting threads will throw
302	tim	1.1	* {@link BrokenBarrierException} and the barrier is placed in the broken
303			* state.
304			*
305			* <p>If the current thread is the last thread to arrive, and a
306			* non-null barrier action was supplied in the constructor, then the
307	dl	1.28	* current thread runs the action before allowing the other threads to
308	tim	1.1	* continue.
309			* If an exception occurs during the barrier action then that exception
310	dholmes	1.13	* will be propagated in the current thread and the barrier is placed in
311			* the broken state.
312	tim	1.1	*
313			* @return the arrival index of the current thread, where index
314	jsr166	1.37	* <tt>{@link #getParties()} - 1</tt> indicates the first
315			* to arrive and zero indicates the last to arrive
316	dl	1.28	* @throws InterruptedException if the current thread was interrupted
317	jsr166	1.37	* while waiting
318	tim	1.1	* @throws BrokenBarrierException if <em>another</em> thread was
319	jsr166	1.37	* interrupted or timed out while the current thread was
320			* waiting, or the barrier was reset, or the barrier was
321			* broken when {@code await} was called, or the barrier
322			* action (if present) failed due an exception.
323	tim	1.1	*/
324			public int await() throws InterruptedException, BrokenBarrierException {
325	dl	1.2	try {
326	dl	1.23	return dowait(false, 0L);
327	tim	1.9	} catch (TimeoutException toe) {
328	dl	1.2	throw new Error(toe); // cannot happen;
329			}
330			}
331
332			/**
333	jsr166	1.37	* Waits until all {@linkplain #getParties parties} have invoked
334			* <tt>await</tt> on this barrier, or the specified waiting time elapses.
335	dl	1.2	*
336			* <p>If the current thread is not the last to arrive then it is
337			* disabled for thread scheduling purposes and lies dormant until
338			* one of the following things happens:
339			* <ul>
340			* <li>The last thread arrives; or
341	dholmes	1.13	* <li>The specified timeout elapses; or
342	jsr166	1.37	* <li>Some other thread {@linkplain Thread#interrupt interrupts}
343			* the current thread; or
344			* <li>Some other thread {@linkplain Thread#interrupt interrupts}
345			* one of the other waiting threads; or
346	dl	1.24	* <li>Some other thread times out while waiting for barrier; or
347	dl	1.2	* <li>Some other thread invokes {@link #reset} on this barrier.
348			* </ul>
349	jsr166	1.37	*
350	dl	1.2	* <p>If the current thread:
351			* <ul>
352			* <li>has its interrupted status set on entry to this method; or
353	jsr166	1.37	* <li>is {@linkplain Thread#interrupt interrupted} while waiting
354	dl	1.2	* </ul>
355			* then {@link InterruptedException} is thrown and the current thread's
356			* interrupted status is cleared.
357			*
358	dl	1.26	* <p>If the specified waiting time elapses then {@link TimeoutException}
359			* is thrown. If the time is less than or equal to zero, the
360			* method will not wait at all.
361			*
362	jsr166	1.37	* <p>If the barrier is {@link #reset} while any thread is waiting,
363			* or if the barrier {@linkplain #isBroken is broken} when
364			* <tt>await</tt> is invoked, or while any thread is waiting, then
365			* {@link BrokenBarrierException} is thrown.
366			*
367			* <p>If any thread is {@linkplain Thread#interrupt interrupted} while
368			* waiting, then all other waiting threads will throw {@link
369			* BrokenBarrierException} and the barrier is placed in the broken
370	dl	1.2	* state.
371			*
372			* <p>If the current thread is the last thread to arrive, and a
373			* non-null barrier action was supplied in the constructor, then the
374	dl	1.28	* current thread runs the action before allowing the other threads to
375	dl	1.2	* continue.
376			* If an exception occurs during the barrier action then that exception
377	dholmes	1.13	* will be propagated in the current thread and the barrier is placed in
378			* the broken state.
379	dl	1.2	*
380	dl	1.5	* @param timeout the time to wait for the barrier
381			* @param unit the time unit of the timeout parameter
382	dl	1.2	* @return the arrival index of the current thread, where index
383	jsr166	1.37	* <tt>{@link #getParties()} - 1</tt> indicates the first
384			* to arrive and zero indicates the last to arrive
385	dl	1.28	* @throws InterruptedException if the current thread was interrupted
386	jsr166	1.37	* while waiting
387			* @throws TimeoutException if the specified timeout elapses
388	dl	1.2	* @throws BrokenBarrierException if <em>another</em> thread was
389	jsr166	1.37	* interrupted or timed out while the current thread was
390			* waiting, or the barrier was reset, or the barrier was broken
391			* when {@code await} was called, or the barrier action (if
392			* present) failed due an exception
393	dl	1.28	*/
394			public int await(long timeout, TimeUnit unit)
395			throws InterruptedException,
396			BrokenBarrierException,
397			TimeoutException {
398	dl	1.2	return dowait(true, unit.toNanos(timeout));
399	tim	1.1	}
400
401			/**
402	dl	1.25	* Queries if this barrier is in a broken state.
403	jsr166	1.37	*
404			* @return {@code true} if one or more parties broke out of this
405			* barrier due to interruption or timeout since
406			* construction or the last reset, or a barrier action
407			* failed due to an exception; {@code false} otherwise.
408	tim	1.1	*/
409			public boolean isBroken() {
410	dl	1.20	final ReentrantLock lock = this.lock;
411	dl	1.2	lock.lock();
412			try {
413	dl	1.28	return generation.broken;
414	tim	1.9	} finally {
415	dl	1.2	lock.unlock();
416			}
417	tim	1.1	}
418
419			/**
420	dl	1.25	* Resets the barrier to its initial state. If any parties are
421	tim	1.1	* currently waiting at the barrier, they will return with a
422	dl	1.8	* {@link BrokenBarrierException}. Note that resets <em>after</em>
423	dl	1.12	* a breakage has occurred for other reasons can be complicated to
424			* carry out; threads need to re-synchronize in some other way,
425			* and choose one to perform the reset. It may be preferable to
426			* instead create a new barrier for subsequent use.
427	tim	1.1	*/
428			public void reset() {
429	dl	1.20	final ReentrantLock lock = this.lock;
430	dl	1.2	lock.lock();
431			try {
432	dl	1.28	breakBarrier(); // break the current generation
433			nextGeneration(); // start a new generation
434	tim	1.9	} finally {
435	dl	1.2	lock.unlock();
436			}
437	tim	1.1	}
438
439			/**
440	dl	1.25	* Returns the number of parties currently waiting at the barrier.
441	tim	1.1	* This method is primarily useful for debugging and assertions.
442			*
443	jsr166	1.37	* @return the number of parties currently blocked in {@link #await}
444	jsr166	1.32	*/
445	tim	1.1	public int getNumberWaiting() {
446	dl	1.20	final ReentrantLock lock = this.lock;
447	dl	1.2	lock.lock();
448			try {
449	dl	1.31	return parties - count;
450	tim	1.9	} finally {
451	dl	1.2	lock.unlock();
452			}
453	tim	1.1	}
454			}