util/concurrent/CyclicBarrier.java

package java.util.concurrent;

/**
 * A <tt>CyclicBarrier</tt> allows a set threads to all wait for each 
 * other to reach a common barrier point.  They are useful in programs
 * involving a fixed sized party of threads that must occasionally
 * wait for each other. The barrier is <em>cyclic</em> because it can
 * be re-used after the waiting threads are released. 
 *
 * <p>A <tt>CyclicBarrier</tt> supports an optional {@link Runnable} command
 * that is run once per barrier point, after the last thread in the party
 * arrives, but before any threads are released. 
 * This <em>barrier action</em> is useful
 * for updating shared-state before any of the parties continue.
 * 
 * <p><b>Sample usage:</b> Here is a code sketch of 
 *  using a barrier in a parallel decomposition design:
 * <pre>
 * class Solver {
 *   final int N;
 *   final float[][] data;
 *   final CyclicBarrier barrier;
 *   
 *   class Worker implements Runnable {
 *     int myRow;
 *     Worker(int row) { myRow = row; }
 *     public void run() {
 *       while (!done()) {
 *         processRow(myRow);
 *
 *         try {
 *           barrier.await(); 
 *         }
 *         catch (InterruptedException ex) { return; }
 *         catch (BrokenBarrierException ex) { return; }
 *       }
 *     }
 *   }
 *
 *   public Solver(float[][] matrix) {
 *     data = matrix;
 *     N = matrix.length;
 *     barrier = new CyclicBarrier(N, 
 *                                 new Runnable() {
 *                                   public void run() { 
 *                                     mergeRows(...); 
 *                                   }
 *                                 });
 *     for (int i = 0; i < N; ++i) 
 *       new Thread(new Worker(i)).start();
 *
 *     waitUntilDone();
 *   }
 * }
 * </pre>
 * Here, each worker thread processes a row of the matrix then waits at the 
 * barrier until all rows have been processed. When all rows are processed
 * the supplied {@link Runnable} barrier action is executed and merges the 
 * rows. If the merger
 * determines that a solution has been found then <tt>done()</tt> will return
 * <tt>true</tt> and each worker will terminate.
 *
 * <p>If the barrier action does not rely on the parties being suspended when
 * it is executed, then any of the threads in the party could execute that
 * action when it is released. To facilitate this, each invocation of
 * {@link #await} returns the arrival index of that thread at the barrier.
 * You can then choose which thread should execute the barrier action, for 
 * example:
 * <pre>  if (barrier.await() == 0) {
 *     // log the completion of this iteration
 *   }</pre>
 *
 * <p>The <tt>CyclicBarrier</tt> uses an all-or-none breakage model for failed
 * synchronization attempts: If a thread leaves a barrier point
 * prematurely because of interruption, all others will also
 * leave abnormally (via {@link BrokenBarrierException}), until the barrier is
 * {@link #reset}. This is usually the simplest and best
 * strategy for sharing knowledge about failures among cooperating
 * threads in the most common usage contexts of barriers.  
 *
 * <h3>Implementation Considerations</h3>
 * <p>This implementation has the property that interruptions among newly
 * arriving threads can cause as-yet-unresumed threads from a previous
 * barrier cycle to return out as broken. This transmits breakage as
 * early as possible, but with the possible byproduct that only some
 * threads returning out of a barrier will realize that it is newly
 * broken. (Others will not realize this until a future cycle.)
 *
 *
 *
 * @since 1.5
 * @spec JSR-166
 * @revised $Date: 2003/04/25 13:27:07 $
 * @editor $Author: dl $
 *
 * @fixme Is the above property actually true in this implementation?
 * @fixme Should we have a timeout version of await()?
 */
public class CyclicBarrier {

    /**
     * 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) {
    }

    /**
     * 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) {
    }

    /**
     * Return the number of parties required to trip this barrier.
     * @return the number of parties required to trip this barrier.
     **/
    public int getParties() {
        return 0; // for now
    }

    /**
     * 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 four 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 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 {
        return 0; // for now
    }

    /**
     * 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 since construction or the last reset;
     * and <tt>false</tt> otherwise.
     */
    public boolean isBroken() {
        return false; // for now
    }

    /**
     * Reset the barrier to its initial state.  If any parties are
     * currently waiting at the barrier, they will return with a
     * {@link BrokenBarrierException}.
     */
    public void reset() {
        // for now
    }

    /**
     * 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() {
        return 0; // for now
    }

}


Revision:	1.1
Committed:	Wed May 14 21:30:46 2003 UTC (21 years ago) by tim
Branch:	MAIN
Log Message:	Moved main source rooted at . to ./src/main Moved test source rooted at ./etc/testcases to ./src/test
#	User	Rev	Content
1	tim	1.1	package java.util.concurrent;
2
3			/**
4			* A <tt>CyclicBarrier</tt> allows a set threads to all wait for each
5			* other to reach a common barrier point. They are useful in programs
6			* involving a fixed sized party of threads that must occasionally
7			* wait for each other. The barrier is <em>cyclic</em> because it can
8			* be re-used after the waiting threads are released.
9			*
10			* <p>A <tt>CyclicBarrier</tt> supports an optional {@link Runnable} command
11			* that is run once per barrier point, after the last thread in the party
12			* arrives, but before any threads are released.
13			* This <em>barrier action</em> is useful
14			* for updating shared-state before any of the parties continue.
15			*
16			* <p><b>Sample usage:</b> Here is a code sketch of
17			* using a barrier in a parallel decomposition design:
18			* <pre>
19			* class Solver {
20			* final int N;
21			* final float[][] data;
22			* final CyclicBarrier barrier;
23			*
24			* class Worker implements Runnable {
25			* int myRow;
26			* Worker(int row) { myRow = row; }
27			* public void run() {
28			* while (!done()) {
29			* processRow(myRow);
30			*
31			* try {
32			* barrier.await();
33			* }
34			* catch (InterruptedException ex) { return; }
35			* catch (BrokenBarrierException ex) { return; }
36			* }
37			* }
38			* }
39			*
40			* public Solver(float[][] matrix) {
41			* data = matrix;
42			* N = matrix.length;
43			* barrier = new CyclicBarrier(N,
44			* new Runnable() {
45			* public void run() {
46			* mergeRows(...);
47			* }
48			* });
49			* for (int i = 0; i < N; ++i)
50			* new Thread(new Worker(i)).start();
51			*
52			* waitUntilDone();
53			* }
54			* }
55			* </pre>
56			* Here, each worker thread processes a row of the matrix then waits at the
57			* barrier until all rows have been processed. When all rows are processed
58			* the supplied {@link Runnable} barrier action is executed and merges the
59			* rows. If the merger
60			* determines that a solution has been found then <tt>done()</tt> will return
61			* <tt>true</tt> and each worker will terminate.
62			*
63			* <p>If the barrier action does not rely on the parties being suspended when
64			* it is executed, then any of the threads in the party could execute that
65			* action when it is released. To facilitate this, each invocation of
66			* {@link #await} returns the arrival index of that thread at the barrier.
67			* You can then choose which thread should execute the barrier action, for
68			* example:
69			* <pre> if (barrier.await() == 0) {
70			* // log the completion of this iteration
71			* }</pre>
72			*
73			* <p>The <tt>CyclicBarrier</tt> uses an all-or-none breakage model for failed
74			* synchronization attempts: If a thread leaves a barrier point
75			* prematurely because of interruption, all others will also
76			* leave abnormally (via {@link BrokenBarrierException}), until the barrier is
77			* {@link #reset}. This is usually the simplest and best
78			* strategy for sharing knowledge about failures among cooperating
79			* threads in the most common usage contexts of barriers.
80			*
81			* <h3>Implementation Considerations</h3>
82			* <p>This implementation has the property that interruptions among newly
83			* arriving threads can cause as-yet-unresumed threads from a previous
84			* barrier cycle to return out as broken. This transmits breakage as
85			* early as possible, but with the possible byproduct that only some
86			* threads returning out of a barrier will realize that it is newly
87			* broken. (Others will not realize this until a future cycle.)
88			*
89			*
90			*
91			* @since 1.5
92			* @spec JSR-166
93			* @revised $Date: 2003/04/25 13:27:07 $
94			* @editor $Author: dl $
95			*
96			* @fixme Is the above property actually true in this implementation?
97			* @fixme Should we have a timeout version of await()?
98			*/
99			public class CyclicBarrier {
100
101			/**
102			* Create a new <tt>CyclicBarrier</tt> that will trip when the
103			* given number of parties (threads) are waiting upon it, and which
104			* will execute the given barrier action when the barrier is tripped.
105			*
106			* @param parties the number of threads that must invoke {@link #await}
107			* before the barrier is tripped.
108			* @param barrierAction the command to execute when the barrier is
109			* tripped.
110			*
111			* @throws IllegalArgumentException if <tt>parties</tt> is less than 1.
112			*/
113			public CyclicBarrier(int parties, Runnable barrierAction) {
114			}
115
116			/**
117			* Create a new <tt>CyclicBarrier</tt> that will trip when the
118			* given number of parties (threads) are waiting upon it.
119			*
120			* <p>This is equivalent to <tt>CyclicBarrier(parties, null)</tt>.
121			*
122			* @param parties the number of threads that must invoke {@link #await}
123			* before the barrier is tripped.
124			*
125			* @throws IllegalArgumentException if <tt>parties</tt> is less than 1.
126			*/
127			public CyclicBarrier(int parties) {
128			}
129
130			/**
131			* Return the number of parties required to trip this barrier.
132			* @return the number of parties required to trip this barrier.
133			**/
134			public int getParties() {
135			return 0; // for now
136			}
137
138			/**
139			* Wait until all {@link #getParties parties} have invoked <tt>await</tt>
140			* on this barrier.
141			*
142			* <p>If the current thread is not the last to arrive then it is
143			* disabled for thread scheduling purposes and lies dormant until
144			* one of four things happens:
145			* <ul>
146			* <li>The last thread arrives; or
147			* <li>Some other thread {@link Thread#interrupt interrupts} the current
148			* thread; or
149			* <li>Some other thread {@link Thread#interrupt interrupts} one of the
150			* other waiting threads; or
151			* <li>Some other thread invokes {@link #reset} on this barrier.
152			* </ul>
153			* <p>If the current thread:
154			* <ul>
155			* <li>has its interrupted status set on entry to this method; or
156			* <li>is {@link Thread#interrupt interrupted} while waiting
157			* </ul>
158			* then {@link InterruptedException} is thrown and the current thread's
159			* interrupted status is cleared.
160			*
161			* <p>If the barrier is {@link #reset} while any thread is waiting, or if
162			* the barrier {@link #isBroken is broken} when <tt>await</tt> is invoked
163			* then {@link BrokenBarrierException} is thrown.
164			*
165			* <p>If any thread is {@link Thread#interrupt interrupted} while waiting,
166			* then all other waiting threads will throw
167			* {@link BrokenBarrierException} and the barrier is placed in the broken
168			* state.
169			*
170			* <p>If the current thread is the last thread to arrive, and a
171			* non-null barrier action was supplied in the constructor, then the
172			* current thread runs the action before allowing the other threads to
173			* continue.
174			* If an exception occurs during the barrier action then that exception
175			* will be propagated in the current thread.
176			*
177			* @return the arrival index of the current thread, where index
178			* <tt>{@link #getParties()} - 1</tt> indicates the first to arrive and
179			* zero indicates the last to arrive.
180			*
181			* @throws InterruptedException if the current thread was interrupted
182			* while waiting
183			* @throws BrokenBarrierException if <em>another</em> thread was
184			* interrupted while the current thread was waiting, or the barrier was
185			* reset, or the barrier was broken when <tt>await</tt> was called.
186			*/
187			public int await() throws InterruptedException, BrokenBarrierException {
188			return 0; // for now
189			}
190
191			/**
192			* Query if this barrier is in a broken state.
193			* @return <tt>true</tt> if one or more parties broke out of this
194			* barrier due to interruption since construction or the last reset;
195			* and <tt>false</tt> otherwise.
196			*/
197			public boolean isBroken() {
198			return false; // for now
199			}
200
201			/**
202			* Reset the barrier to its initial state. If any parties are
203			* currently waiting at the barrier, they will return with a
204			* {@link BrokenBarrierException}.
205			*/
206			public void reset() {
207			// for now
208			}
209
210			/**
211			* Return the number of parties currently waiting at the barrier.
212			* This method is primarily useful for debugging and assertions.
213			*
214			* @return the number of parties currently blocked in {@link #await}
215			**/
216			public int getNumberWaiting() {
217			return 0; // for now
218			}
219
220			}
221
222