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;

import java.util.concurrent.atomic.AtomicInteger;

/**
 * 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 upon construction, but the workQueue field is
     * not set until the thread has started (unless forced early by a
     * subclass constructor call to poolIndex()).  This provides
     * better memory placement (because this thread allocates queue
     * and bookkeeping fields) but because the field is non-final, we
     * require that it never be accessed except by the owning thread.
     */

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

    /**
     * Sequence number for creating worker Names
     */
    private static final AtomicInteger threadNumber = new AtomicInteger();

    /**
     * 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) {
        super(pool.workerNamePrefix.concat(Integer.toString(threadNumber.incrementAndGet())));
        setDaemon(true);
        this.pool = pool;
        Thread.UncaughtExceptionHandler ueh = pool.ueh;
        if (ueh != null)
            setUncaughtExceptionHandler(ueh);
    }

    /**
     * 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() {
        // force early registration if called before started
        ForkJoinPool.WorkQueue q;
        if ((q = workQueue) == null) {
            pool.registerWorker(this);
            q = workQueue;
        }
        return q.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 {
            pool.registerWorker(this);
            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:	1.3
Committed:	Mon Nov 19 18:12:28 2012 UTC (11 years, 5 months ago) by dl
Branch:	MAIN
Changes since 1.2:	+24 -15 lines
Log Message:	better memory positioning
#	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 jsr166e;
8
9	import java.util.concurrent.atomic.AtomicInteger;
10
11	/**
12	* A thread managed by a {@link ForkJoinPool}, which executes
13	* {@link ForkJoinTask}s.
14	* This class is subclassable solely for the sake of adding
15	* functionality -- there are no overridable methods dealing with
16	* scheduling or execution. However, you can override initialization
17	* and termination methods surrounding the main task processing loop.
18	* If you do create such a subclass, you will also need to supply a
19	* custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to use it
20	* in a {@code ForkJoinPool}.
21	*
22	* @since 1.7
23	* @author Doug Lea
24	*/
25	public class ForkJoinWorkerThread extends Thread {
26	/*
27	* ForkJoinWorkerThreads are managed by ForkJoinPools and perform
28	* ForkJoinTasks. For explanation, see the internal documentation
29	* of class ForkJoinPool.
30	*
31	* This class just maintains links to its pool and WorkQueue. The
32	* pool field is set upon construction, but the workQueue field is
33	* not set until the thread has started (unless forced early by a
34	* subclass constructor call to poolIndex()). This provides
35	* better memory placement (because this thread allocates queue
36	* and bookkeeping fields) but because the field is non-final, we
37	* require that it never be accessed except by the owning thread.
38	*/
39
40	final ForkJoinPool pool; // the pool this thread works in
41	ForkJoinPool.WorkQueue workQueue; // Work-stealing mechanics
42
43	/**
44	* Sequence number for creating worker Names
45	*/
46	private static final AtomicInteger threadNumber = new AtomicInteger();
47
48	/**
49	* Creates a ForkJoinWorkerThread operating in the given pool.
50	*
51	* @param pool the pool this thread works in
52	* @throws NullPointerException if pool is null
53	*/
54	protected ForkJoinWorkerThread(ForkJoinPool pool) {
55	super(pool.workerNamePrefix.concat(Integer.toString(threadNumber.incrementAndGet())));
56	setDaemon(true);
57	this.pool = pool;
58	Thread.UncaughtExceptionHandler ueh = pool.ueh;
59	if (ueh != null)
60	setUncaughtExceptionHandler(ueh);
61	}
62
63	/**
64	* Returns the pool hosting this thread.
65	*
66	* @return the pool
67	*/
68	public ForkJoinPool getPool() {
69	return pool;
70	}
71
72	/**
73	* Returns the index number of this thread in its pool. The
74	* returned value ranges from zero to the maximum number of
75	* threads (minus one) that have ever been created in the pool.
76	* This method may be useful for applications that track status or
77	* collect results per-worker rather than per-task.
78	*
79	* @return the index number
80	*/
81	public int getPoolIndex() {
82	// force early registration if called before started
83	ForkJoinPool.WorkQueue q;
84	if ((q = workQueue) == null) {
85	pool.registerWorker(this);
86	q = workQueue;
87	}
88	return q.poolIndex;
89	}
90
91	/**
92	* Initializes internal state after construction but before
93	* processing any tasks. If you override this method, you must
94	* invoke {@code super.onStart()} at the beginning of the method.
95	* Initialization requires care: Most fields must have legal
96	* default values, to ensure that attempted accesses from other
97	* threads work correctly even before this thread starts
98	* processing tasks.
99	*/
100	protected void onStart() {
101	}
102
103	/**
104	* Performs cleanup associated with termination of this worker
105	* thread. If you override this method, you must invoke
106	* {@code super.onTermination} at the end of the overridden method.
107	*
108	* @param exception the exception causing this thread to abort due
109	* to an unrecoverable error, or {@code null} if completed normally
110	*/
111	protected void onTermination(Throwable exception) {
112	}
113
114	/**
115	* This method is required to be public, but should never be
116	* called explicitly. It performs the main run loop to execute
117	* {@link ForkJoinTask}s.
118	*/
119	public void run() {
120	Throwable exception = null;
121	try {
122	pool.registerWorker(this);
123	onStart();
124	pool.runWorker(workQueue);
125	} catch (Throwable ex) {
126	exception = ex;
127	} finally {
128	try {
129	onTermination(exception);
130	} catch (Throwable ex) {
131	if (exception == null)
132	exception = ex;
133	} finally {
134	pool.deregisterWorker(this, exception);
135	}
136	}
137	}
138	}