src/jsr166e/ForkJoinWorkerThread.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/publicdomain/zero/1.0/
 */

package jsr166e;

/**
 * A thread managed by a {@link ForkJoinPool}, which executes
 * {@link ForkJoinTask}s.
 * This class is subclassable solely for the sake of adding
 * functionality -- there are no overridable methods dealing with
 * scheduling or execution.  However, you can override initialization
 * and termination methods surrounding the main task processing loop.
 * If you do create such a subclass, you will also need to supply a
 * custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to
 * {@linkplain ForkJoinPool#ForkJoinPool use it} in a {@code ForkJoinPool}.
 *
 * @since 1.7
 * @author Doug Lea
 */
public class ForkJoinWorkerThread extends Thread {
    /*
     * ForkJoinWorkerThreads are managed by ForkJoinPools and perform
     * ForkJoinTasks. For explanation, see the internal documentation
     * of class ForkJoinPool.
     *
     * This class just maintains links to its pool and WorkQueue.  The
     * pool field is set immediately upon construction, but the
     * workQueue field is not set until a call to registerWorker
     * completes. This leads to a visibility race, that is tolerated
     * by requiring that the workQueue field is only accessed by the
     * owning thread.
     */

    final ForkJoinPool pool;                // the pool this thread works in
    final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics

    /**
     * Creates a ForkJoinWorkerThread operating in the given pool.
     *
     * @param pool the pool this thread works in
     * @throws NullPointerException if pool is null
     */
    protected ForkJoinWorkerThread(ForkJoinPool pool) {
        // Use a placeholder until a useful name can be set in registerWorker
        super("aForkJoinWorkerThread");
        this.pool = pool;
        this.workQueue = pool.registerWorker(this);
    }

    /**
     * Returns the pool hosting this thread.
     *
     * @return the pool
     */
    public ForkJoinPool getPool() {
        return pool;
    }

    /**
     * Returns the unique index number of this thread in its pool.
     * The returned value ranges from zero to the maximum number of
     * threads (minus one) that may exist in the pool, and does not
     * change during the lifetime of the thread.  This method may be
     * useful for applications that track status or collect results
     * per-worker-thread rather than per-task.
     *
     * @return the index number
     */
    public int getPoolIndex() {
        return workQueue.poolIndex >>> 1; // ignore odd/even tag bit
    }

    /**
     * Initializes internal state after construction but before
     * processing any tasks. If you override this method, you must
     * invoke {@code super.onStart()} at the beginning of the method.
     * Initialization requires care: Most fields must have legal
     * default values, to ensure that attempted accesses from other
     * threads work correctly even before this thread starts
     * processing tasks.
     */
    protected void onStart() {
    }

    /**
     * Performs cleanup associated with termination of this worker
     * thread.  If you override this method, you must invoke
     * {@code super.onTermination} at the end of the overridden method.
     *
     * @param exception the exception causing this thread to abort due
     * to an unrecoverable error, or {@code null} if completed normally
     */
    protected void onTermination(Throwable exception) {
    }

    /**
     * This method is required to be public, but should never be
     * called explicitly. It performs the main run loop to execute
     * {@link ForkJoinTask}s.
     */
    public void run() {
        Throwable exception = null;
        try {
            onStart();
            pool.runWorker(workQueue);
        } catch (Throwable ex) {
            exception = ex;
        } finally {
            try {
                onTermination(exception);
            } catch (Throwable ex) {
                if (exception == null)
                    exception = ex;
            } finally {
                pool.deregisterWorker(this, exception);
            }
        }
    }
}
Revision:	1.6
Committed:	Sun Jan 18 20:17:33 2015 UTC (9 years, 3 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.5:	+0 -1 lines
Log Message:	exactly one blank line before and after package statements
#	User	Rev	Content
1	dl	1.1	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain, as explained at
4			* http://creativecommons.org/publicdomain/zero/1.0/
5			*/
6
7			package jsr166e;
8
9			/**
10			* A thread managed by a {@link ForkJoinPool}, which executes
11			* {@link ForkJoinTask}s.
12			* This class is subclassable solely for the sake of adding
13			* functionality -- there are no overridable methods dealing with
14			* scheduling or execution. However, you can override initialization
15			* and termination methods surrounding the main task processing loop.
16			* If you do create such a subclass, you will also need to supply a
17	dl	1.5	* custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to
18			* {@linkplain ForkJoinPool#ForkJoinPool use it} in a {@code ForkJoinPool}.
19	dl	1.1	*
20			* @since 1.7
21			* @author Doug Lea
22			*/
23			public class ForkJoinWorkerThread extends Thread {
24			/*
25			* ForkJoinWorkerThreads are managed by ForkJoinPools and perform
26			* ForkJoinTasks. For explanation, see the internal documentation
27			* of class ForkJoinPool.
28	dl	1.3	*
29			* This class just maintains links to its pool and WorkQueue. The
30	dl	1.4	* pool field is set immediately upon construction, but the
31			* workQueue field is not set until a call to registerWorker
32			* completes. This leads to a visibility race, that is tolerated
33			* by requiring that the workQueue field is only accessed by the
34			* owning thread.
35	dl	1.1	*/
36
37			final ForkJoinPool pool; // the pool this thread works in
38	dl	1.4	final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics
39	dl	1.2
40			/**
41	dl	1.1	* Creates a ForkJoinWorkerThread operating in the given pool.
42			*
43			* @param pool the pool this thread works in
44			* @throws NullPointerException if pool is null
45			*/
46			protected ForkJoinWorkerThread(ForkJoinPool pool) {
47	dl	1.4	// Use a placeholder until a useful name can be set in registerWorker
48			super("aForkJoinWorkerThread");
49	dl	1.3	this.pool = pool;
50	dl	1.4	this.workQueue = pool.registerWorker(this);
51	dl	1.1	}
52
53			/**
54			* Returns the pool hosting this thread.
55			*
56			* @return the pool
57			*/
58			public ForkJoinPool getPool() {
59			return pool;
60			}
61
62			/**
63	dl	1.5	* Returns the unique index number of this thread in its pool.
64			* The returned value ranges from zero to the maximum number of
65			* threads (minus one) that may exist in the pool, and does not
66			* change during the lifetime of the thread. This method may be
67			* useful for applications that track status or collect results
68			* per-worker-thread rather than per-task.
69	dl	1.1	*
70			* @return the index number
71			*/
72			public int getPoolIndex() {
73	dl	1.5	return workQueue.poolIndex >>> 1; // ignore odd/even tag bit
74	dl	1.1	}
75
76			/**
77			* Initializes internal state after construction but before
78			* processing any tasks. If you override this method, you must
79			* invoke {@code super.onStart()} at the beginning of the method.
80			* Initialization requires care: Most fields must have legal
81			* default values, to ensure that attempted accesses from other
82			* threads work correctly even before this thread starts
83			* processing tasks.
84			*/
85			protected void onStart() {
86			}
87
88			/**
89			* Performs cleanup associated with termination of this worker
90			* thread. If you override this method, you must invoke
91			* {@code super.onTermination} at the end of the overridden method.
92			*
93			* @param exception the exception causing this thread to abort due
94			* to an unrecoverable error, or {@code null} if completed normally
95			*/
96			protected void onTermination(Throwable exception) {
97			}
98
99			/**
100			* This method is required to be public, but should never be
101			* called explicitly. It performs the main run loop to execute
102			* {@link ForkJoinTask}s.
103			*/
104			public void run() {
105			Throwable exception = null;
106			try {
107			onStart();
108			pool.runWorker(workQueue);
109			} catch (Throwable ex) {
110			exception = ex;
111			} finally {
112			try {
113			onTermination(exception);
114			} catch (Throwable ex) {
115			if (exception == null)
116			exception = ex;
117			} finally {
118			pool.deregisterWorker(this, exception);
119			}
120			}
121			}
122			}