src/jsr166y/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 jsr166y;

/**
 * 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 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 index number of this thread in its pool.  The
     * returned value ranges from zero to the maximum number of
     * threads (minus one) that have ever been created in the pool.
     * This method may be useful for applications that track status or
     * collect results per-worker rather than per-task.
     *
     * @return the index number
     */
    public int getPoolIndex() {
        return workQueue.poolIndex;
    }

    /**
     * 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:	1.73
Committed:	Wed Nov 21 19:54:39 2012 UTC (11 years, 4 months ago) by dl
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.72:	+10 -27 lines
Log Message:	stabilize
#	Content
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 jsr166y;
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	* custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to use it
18	* in a {@code ForkJoinPool}.
19	*
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	*
29	* This class just maintains links to its pool and WorkQueue. The
30	* 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	*/
36
37	final ForkJoinPool pool; // the pool this thread works in
38	final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics
39
40	/**
41	* 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	// Use a placeholder until a useful name can be set in registerWorker
48	super("aForkJoinWorkerThread");
49	this.pool = pool;
50	this.workQueue = pool.registerWorker(this);
51	}
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	* Returns the index number of this thread in its pool. The
64	* returned value ranges from zero to the maximum number of
65	* threads (minus one) that have ever been created in the pool.
66	* This method may be useful for applications that track status or
67	* collect results per-worker rather than per-task.
68	*
69	* @return the index number
70	*/
71	public int getPoolIndex() {
72	return workQueue.poolIndex;
73	}
74
75	/**
76	* Initializes internal state after construction but before
77	* processing any tasks. If you override this method, you must
78	* invoke {@code super.onStart()} at the beginning of the method.
79	* Initialization requires care: Most fields must have legal
80	* default values, to ensure that attempted accesses from other
81	* threads work correctly even before this thread starts
82	* processing tasks.
83	*/
84	protected void onStart() {
85	}
86
87	/**
88	* Performs cleanup associated with termination of this worker
89	* thread. If you override this method, you must invoke
90	* {@code super.onTermination} at the end of the overridden method.
91	*
92	* @param exception the exception causing this thread to abort due
93	* to an unrecoverable error, or {@code null} if completed normally
94	*/
95	protected void onTermination(Throwable exception) {
96	}
97
98	/**
99	* This method is required to be public, but should never be
100	* called explicitly. It performs the main run loop to execute
101	* {@link ForkJoinTask}s.
102	*/
103	public void run() {
104	Throwable exception = null;
105	try {
106	onStart();
107	pool.runWorker(workQueue);
108	} catch (Throwable ex) {
109	exception = ex;
110	} finally {
111	try {
112	onTermination(exception);
113	} catch (Throwable ex) {
114	if (exception == null)
115	exception = ex;
116	} finally {
117	pool.deregisterWorker(this, exception);
118	}
119	}
120	}
121	}