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).
 *
 * @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;
        boolean tripped = 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
        generation.tripped = true;
        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) {
                    breakBarrier();
                    throw ie;
                }

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

                if (g.tripped)
                    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 <tt>null</tt> if there is no action.
     *
     * @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;
    }

    /**
     * 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 <tt>parties</tt> 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 {@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,
     * or while any thread is waiting,
     * 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 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
     * <tt>await</tt> 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 {@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 specified 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 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 {@link #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 {@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 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
     * <tt>await</tt> 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 <tt>true</tt> 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;
     * <tt>false</tt> 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:	1.32
Committed:	Tue Apr 26 01:55:35 2005 UTC (19 years, 1 month ago) by jsr166
Branch:	MAIN
Changes since 1.31:	+1 -1 lines
Log Message:	doc fixes
#	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			* @since 1.5
92	brian	1.4	* @see CountDownLatch
93	tim	1.1	*
94	dl	1.5	* @author Doug Lea
95	tim	1.1	*/
96			public class CyclicBarrier {
97	dl	1.28	/**
98			* Each use of the barrier is represented as a generation instance.
99			* The generation changes whenever the barrier is tripped, or
100			* is reset. There can be many generations associated with threads
101			* using the barrier - due to the non-deterministic way the lock
102			* may be allocated to waiting threads - but only one of these
103			* can be active at a time (the one to which <tt>count</tt> applies)
104			* and all the rest are either broken or tripped.
105			* There need not be an active generation if there has been a break
106			* but no subsequent reset.
107			*/
108			private static class Generation {
109			boolean broken = false;
110			boolean tripped = false;
111			}
112
113	dl	1.5	/** The lock for guarding barrier entry */
114	dl	1.2	private final ReentrantLock lock = new ReentrantLock();
115	dl	1.5	/** Condition to wait on until tripped */
116	dl	1.21	private final Condition trip = lock.newCondition();
117	dl	1.5	/** The number of parties */
118	dl	1.2	private final int parties;
119	dl	1.5	/* The command to run when tripped */
120	dl	1.12	private final Runnable barrierCommand;
121	dl	1.28	/** The current generation */
122			private Generation generation = new Generation();
123	dl	1.2
124			/**
125			* Number of parties still waiting. Counts down from parties to 0
126	dl	1.31	* on each generation. It is reset to parties on each new
127			* generation or when broken.
128	dl	1.2	*/
129	dl	1.28	private int count;
130	dl	1.2
131			/**
132	jsr166	1.29	* Updates state on barrier trip and wakes up everyone.
133	dl	1.28	* Called only while holding lock.
134			*/
135	dl	1.2	private void nextGeneration() {
136	dl	1.28	// signal completion of last generation
137			generation.tripped = true;
138			trip.signalAll();
139			// set up next generation
140	dl	1.2	count = parties;
141	dl	1.28	generation = new Generation();
142	dl	1.12	}
143
144			/**
145	jsr166	1.29	* Sets current barrier generation as broken and wakes up everyone.
146	dl	1.28	* Called only while holding lock.
147	dl	1.12	*/
148			private void breakBarrier() {
149	dl	1.28	generation.broken = true;
150	dl	1.31	count = parties;
151	dl	1.12	trip.signalAll();
152	dl	1.2	}
153
154	dl	1.5	/**
155	dl	1.7	* Main barrier code, covering the various policies.
156	dl	1.5	*/
157	dl	1.28	private int dowait(boolean timed, long nanos)
158			throws InterruptedException, BrokenBarrierException,
159			TimeoutException {
160	dl	1.20	final ReentrantLock lock = this.lock;
161	dl	1.2	lock.lock();
162			try {
163	dl	1.30	final Generation g = generation;
164	dl	1.2
165	dl	1.28	if (g.broken)
166	dl	1.2	throw new BrokenBarrierException();
167
168			if (Thread.interrupted()) {
169	dl	1.12	breakBarrier();
170	dl	1.2	throw new InterruptedException();
171			}
172
173	dl	1.30	int index = --count;
174			if (index == 0) { // tripped
175			boolean ranAction = false;
176			try {
177	dl	1.31	final Runnable command = barrierCommand;
178			if (command != null)
179			command.run();
180	dl	1.30	ranAction = true;
181			nextGeneration();
182			return 0;
183			} finally {
184			if (!ranAction)
185			breakBarrier();
186			}
187			}
188	dl	1.2
189	dl	1.28	// loop until tripped, broken, interrupted, or timed out
190	dl	1.12	for (;;) {
191	dl	1.2	try {
192	dl	1.28	if (!timed)
193	dl	1.2	trip.await();
194	dl	1.23	else if (nanos > 0L)
195	dl	1.2	nanos = trip.awaitNanos(nanos);
196	dl	1.12	} catch (InterruptedException ie) {
197			breakBarrier();
198			throw ie;
199	dl	1.2	}
200	dl	1.28
201	dl	1.30	if (g.broken)
202	dl	1.12	throw new BrokenBarrierException();
203
204	dl	1.28	if (g.tripped)
205	dl	1.12	return index;
206
207	dl	1.23	if (timed && nanos <= 0L) {
208	dl	1.12	breakBarrier();
209	dl	1.2	throw new TimeoutException();
210			}
211			}
212	tim	1.9	} finally {
213	dl	1.2	lock.unlock();
214			}
215			}
216	tim	1.1
217			/**
218	dl	1.25	* Creates a new <tt>CyclicBarrier</tt> that will trip when the
219	tim	1.1	* given number of parties (threads) are waiting upon it, and which
220	dl	1.17	* will execute the given barrier action when the barrier is tripped,
221	dl	1.19	* performed by the last thread entering the barrier.
222	tim	1.1	*
223			* @param parties the number of threads that must invoke {@link #await}
224			* before the barrier is tripped.
225			* @param barrierAction the command to execute when the barrier is
226	dl	1.15	* tripped, or <tt>null</tt> if there is no action.
227	tim	1.1	*
228			* @throws IllegalArgumentException if <tt>parties</tt> is less than 1.
229			*/
230			public CyclicBarrier(int parties, Runnable barrierAction) {
231	dl	1.2	if (parties <= 0) throw new IllegalArgumentException();
232	dl	1.28	this.parties = parties;
233	dl	1.2	this.count = parties;
234			this.barrierCommand = barrierAction;
235	tim	1.1	}
236
237			/**
238	dl	1.25	* Creates a new <tt>CyclicBarrier</tt> that will trip when the
239	dl	1.14	* given number of parties (threads) are waiting upon it, and
240	dl	1.31	* does not perform a predefined action when the barrier is tripped.
241	tim	1.1	*
242			* @param parties the number of threads that must invoke {@link #await}
243			* before the barrier is tripped.
244			*
245			* @throws IllegalArgumentException if <tt>parties</tt> is less than 1.
246			*/
247			public CyclicBarrier(int parties) {
248	dl	1.2	this(parties, null);
249	tim	1.1	}
250
251			/**
252	dl	1.25	* Returns the number of parties required to trip this barrier.
253	tim	1.1	* @return the number of parties required to trip this barrier.
254	dl	1.31	*/
255	tim	1.1	public int getParties() {
256	dl	1.2	return parties;
257	tim	1.1	}
258
259			/**
260	dl	1.25	* Waits until all {@link #getParties parties} have invoked <tt>await</tt>
261	tim	1.1	* on this barrier.
262			*
263			* <p>If the current thread is not the last to arrive then it is
264			* disabled for thread scheduling purposes and lies dormant until
265	dl	1.2	* one of following things happens:
266	tim	1.1	* <ul>
267			* <li>The last thread arrives; or
268			* <li>Some other thread {@link Thread#interrupt interrupts} the current
269			* thread; or
270			* <li>Some other thread {@link Thread#interrupt interrupts} one of the
271			* other waiting threads; or
272	dl	1.24	* <li>Some other thread times out while waiting for barrier; or
273	tim	1.1	* <li>Some other thread invokes {@link #reset} on this barrier.
274			* </ul>
275			* <p>If the current thread:
276			* <ul>
277			* <li>has its interrupted status set on entry to this method; or
278			* <li>is {@link Thread#interrupt interrupted} while waiting
279			* </ul>
280			* then {@link InterruptedException} is thrown and the current thread's
281			* interrupted status is cleared.
282			*
283	dl	1.28	* <p>If the barrier is {@link #reset} while any thread is waiting, or if
284	dholmes	1.13	* the barrier {@link #isBroken is broken} when <tt>await</tt> is invoked,
285	dl	1.16	* or while any thread is waiting,
286	tim	1.1	* then {@link BrokenBarrierException} is thrown.
287			*
288			* <p>If any thread is {@link Thread#interrupt interrupted} while waiting,
289	dl	1.28	* then all other waiting threads will throw
290	tim	1.1	* {@link BrokenBarrierException} and the barrier is placed in the broken
291			* state.
292			*
293			* <p>If the current thread is the last thread to arrive, and a
294			* non-null barrier action was supplied in the constructor, then the
295	dl	1.28	* current thread runs the action before allowing the other threads to
296	tim	1.1	* continue.
297			* If an exception occurs during the barrier action then that exception
298	dholmes	1.13	* will be propagated in the current thread and the barrier is placed in
299			* the broken state.
300	tim	1.1	*
301			* @return the arrival index of the current thread, where index
302	dl	1.28	* <tt>{@link #getParties()} - 1</tt> indicates the first to arrive and
303	tim	1.1	* zero indicates the last to arrive.
304			*
305	dl	1.28	* @throws InterruptedException if the current thread was interrupted
306	jsr166	1.29	* while waiting.
307	tim	1.1	* @throws BrokenBarrierException if <em>another</em> thread was
308	dl	1.28	* interrupted or timed out while the current thread was waiting,
309			* or the barrier was reset, or the barrier was broken when
310			* <tt>await</tt> was called, or the barrier action (if present)
311			* failed due an exception.
312	tim	1.1	*/
313			public int await() throws InterruptedException, BrokenBarrierException {
314	dl	1.2	try {
315	dl	1.23	return dowait(false, 0L);
316	tim	1.9	} catch (TimeoutException toe) {
317	dl	1.2	throw new Error(toe); // cannot happen;
318			}
319			}
320
321			/**
322	dl	1.25	* Waits until all {@link #getParties parties} have invoked <tt>await</tt>
323	dl	1.2	* on this barrier.
324			*
325			* <p>If the current thread is not the last to arrive then it is
326			* disabled for thread scheduling purposes and lies dormant until
327			* one of the following things happens:
328			* <ul>
329			* <li>The last thread arrives; or
330	dholmes	1.13	* <li>The specified timeout elapses; or
331	dl	1.2	* <li>Some other thread {@link Thread#interrupt interrupts} the current
332			* thread; or
333			* <li>Some other thread {@link Thread#interrupt interrupts} one of the
334			* other waiting threads; or
335	dl	1.24	* <li>Some other thread times out while waiting for barrier; or
336	dl	1.2	* <li>Some other thread invokes {@link #reset} on this barrier.
337			* </ul>
338			* <p>If the current thread:
339			* <ul>
340			* <li>has its interrupted status set on entry to this method; or
341			* <li>is {@link Thread#interrupt interrupted} while waiting
342			* </ul>
343			* then {@link InterruptedException} is thrown and the current thread's
344			* interrupted status is cleared.
345			*
346	dl	1.26	* <p>If the specified waiting time elapses then {@link TimeoutException}
347			* is thrown. If the time is less than or equal to zero, the
348			* method will not wait at all.
349			*
350	dl	1.28	* <p>If the barrier is {@link #reset} while any thread is waiting, or if
351	dholmes	1.13	* the barrier {@link #isBroken is broken} when <tt>await</tt> is invoked,
352	dl	1.16	* or while any thread is waiting,
353	dl	1.2	* then {@link BrokenBarrierException} is thrown.
354			*
355			* <p>If any thread is {@link Thread#interrupt interrupted} while waiting,
356	dl	1.28	* then all other waiting threads will throw
357	dl	1.2	* {@link BrokenBarrierException} and the barrier is placed in the broken
358			* state.
359			*
360			* <p>If the current thread is the last thread to arrive, and a
361			* non-null barrier action was supplied in the constructor, then the
362	dl	1.28	* current thread runs the action before allowing the other threads to
363	dl	1.2	* continue.
364			* If an exception occurs during the barrier action then that exception
365	dholmes	1.13	* will be propagated in the current thread and the barrier is placed in
366			* the broken state.
367	dl	1.2	*
368	dl	1.5	* @param timeout the time to wait for the barrier
369			* @param unit the time unit of the timeout parameter
370	dl	1.2	* @return the arrival index of the current thread, where index
371	jsr166	1.29	* <tt>{@link #getParties()} - 1</tt> indicates the first to arrive and
372	dl	1.2	* zero indicates the last to arrive.
373			*
374	dl	1.28	* @throws InterruptedException if the current thread was interrupted
375	jsr166	1.29	* while waiting.
376	dl	1.2	* @throws TimeoutException if the specified timeout elapses.
377			* @throws BrokenBarrierException if <em>another</em> thread was
378	dl	1.28	* interrupted or timed out while the current thread was waiting,
379			* or the barrier was reset, or the barrier was broken when
380			* <tt>await</tt> was called, or the barrier action (if present)
381			* failed due an exception.
382			*/
383			public int await(long timeout, TimeUnit unit)
384			throws InterruptedException,
385			BrokenBarrierException,
386			TimeoutException {
387	dl	1.2	return dowait(true, unit.toNanos(timeout));
388	tim	1.1	}
389
390			/**
391	dl	1.25	* Queries if this barrier is in a broken state.
392	tim	1.1	* @return <tt>true</tt> if one or more parties broke out of this
393	dl	1.2	* barrier due to interruption or timeout since construction or
394	dl	1.28	* the last reset, or a barrier action failed due to an exception;
395	jsr166	1.29	* <tt>false</tt> otherwise.
396	tim	1.1	*/
397			public boolean isBroken() {
398	dl	1.20	final ReentrantLock lock = this.lock;
399	dl	1.2	lock.lock();
400			try {
401	dl	1.28	return generation.broken;
402	tim	1.9	} finally {
403	dl	1.2	lock.unlock();
404			}
405	tim	1.1	}
406
407			/**
408	dl	1.25	* Resets the barrier to its initial state. If any parties are
409	tim	1.1	* currently waiting at the barrier, they will return with a
410	dl	1.8	* {@link BrokenBarrierException}. Note that resets <em>after</em>
411	dl	1.12	* a breakage has occurred for other reasons can be complicated to
412			* carry out; threads need to re-synchronize in some other way,
413			* and choose one to perform the reset. It may be preferable to
414			* instead create a new barrier for subsequent use.
415	tim	1.1	*/
416			public void reset() {
417	dl	1.20	final ReentrantLock lock = this.lock;
418	dl	1.2	lock.lock();
419			try {
420	dl	1.28	breakBarrier(); // break the current generation
421			nextGeneration(); // start a new generation
422	tim	1.9	} finally {
423	dl	1.2	lock.unlock();
424			}
425	tim	1.1	}
426
427			/**
428	dl	1.25	* Returns the number of parties currently waiting at the barrier.
429	tim	1.1	* This method is primarily useful for debugging and assertions.
430			*
431	jsr166	1.29	* @return the number of parties currently blocked in {@link #await}.
432	jsr166	1.32	*/
433	tim	1.1	public int getNumberWaiting() {
434	dl	1.20	final ReentrantLock lock = this.lock;
435	dl	1.2	lock.lock();
436			try {
437	dl	1.31	return parties - count;
438	tim	1.9	} finally {
439	dl	1.2	lock.unlock();
440			}
441	tim	1.1	}
442			}