util/concurrent/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 java.util.concurrent;

import java.security.AccessController;
import java.security.PrivilegedAction;

/**
 * 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(int, ForkJoinWorkerThreadFactory,
 * UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)
 * 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.
     */

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

    /**
     * Full nonpublic constructor.
     */
    ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool,
                         boolean useSystemClassLoader, boolean isInnocuous) {
        super(group, null, pool.nextWorkerThreadName(), 0L);
        UncaughtExceptionHandler handler = (this.pool = pool).ueh;
        this.workQueue = new ForkJoinPool.WorkQueue(this, isInnocuous);
        super.setDaemon(true);
        if (handler != null)
            super.setUncaughtExceptionHandler(handler);
        if (useSystemClassLoader)
            super.setContextClassLoader(ClassLoader.getSystemClassLoader());
    }

    /**
     * Creates a ForkJoinWorkerThread operating in the given thread group and
     * pool.
     *
     * @param group if non-null, the thread group for this thread
     * @param pool the pool this thread works in
     * @throws NullPointerException if pool is null
     */
    /* TODO: protected */ ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool) {
        this(group, pool, false, false);
    }

    /**
     * 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) {
        this(null, pool, false, false);
    }

    /**
     * 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.getPoolIndex();
    }

    /**
     * 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;
        ForkJoinPool p = pool;
        ForkJoinPool.WorkQueue w = workQueue;
        if (p != null && w != null) {   // skip on failed initialization
            try {
                p.registerWorker(w);
                onStart();
                p.runWorker(w);
            } catch (Throwable ex) {
                exception = ex;
            } finally {
                try {
                    onTermination(exception);
                } catch (Throwable ex) {
                    if (exception == null)
                        exception = ex;
                } finally {
                    p.deregisterWorker(this, exception);
                }
            }
        }
    }

    /**
     * A worker thread that has no permissions, is not a member of any
     * user-defined ThreadGroup, uses the system class loader as
     * thread context class loader, and erases all ThreadLocals after
     * running each top-level task.
     */
    static final class InnocuousForkJoinWorkerThread extends ForkJoinWorkerThread {
        /** The ThreadGroup for all InnocuousForkJoinWorkerThreads */
        private static final ThreadGroup innocuousThreadGroup =
            AccessController.doPrivileged(new PrivilegedAction<>() {
                public ThreadGroup run() {
                    ThreadGroup group = Thread.currentThread().getThreadGroup();
                    for (ThreadGroup p; (p = group.getParent()) != null; )
                        group = p;
                    return new ThreadGroup(
                        group, "InnocuousForkJoinWorkerThreadGroup");
                }});

        InnocuousForkJoinWorkerThread(ForkJoinPool pool) {
            super(innocuousThreadGroup, pool, true, true);
        }

        @Override // to silently fail
        public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { }

        @Override // paranoically
        public void setContextClassLoader(ClassLoader cl) {
            if (cl != null && ClassLoader.getSystemClassLoader() != cl)
                throw new SecurityException("setContextClassLoader");
        }
    }
}
Revision:	1.82
Committed:	Sun Dec 6 18:10:00 2020 UTC (3 years, 5 months ago) by jsr166
Branch:	MAIN
Changes since 1.81:	+1 -1 lines
Log Message:	ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool): demote to package-private, for now
#	User	Rev	Content
1	jsr166	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	jsr166	1.46	* http://creativecommons.org/publicdomain/zero/1.0/
5	jsr166	1.1	*/
6
7			package java.util.concurrent;
8
9	jsr166	1.74	import java.security.AccessController;
10			import java.security.PrivilegedAction;
11	dl	1.60
12	jsr166	1.1	/**
13	jsr166	1.40	* A thread managed by a {@link ForkJoinPool}, which executes
14			* {@link ForkJoinTask}s.
15			* This class is subclassable solely for the sake of adding
16			* functionality -- there are no overridable methods dealing with
17			* scheduling or execution. However, you can override initialization
18			* and termination methods surrounding the main task processing loop.
19			* If you do create such a subclass, you will also need to supply a
20	jsr166	1.57	* custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to
21	jsr166	1.76	* {@linkplain ForkJoinPool#ForkJoinPool(int, ForkJoinWorkerThreadFactory,
22			* UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)
23			* use it} in a {@code ForkJoinPool}.
24	jsr166	1.1	*
25			* @since 1.7
26			* @author Doug Lea
27			*/
28			public class ForkJoinWorkerThread extends Thread {
29			/*
30	dl	1.14	* ForkJoinWorkerThreads are managed by ForkJoinPools and perform
31	dl	1.52	* ForkJoinTasks. For explanation, see the internal documentation
32			* of class ForkJoinPool.
33	dl	1.55	*
34	dl	1.79	* This class just maintains links to its pool and WorkQueue.
35	jsr166	1.1	*/
36
37	dl	1.52	final ForkJoinPool pool; // the pool this thread works in
38	dl	1.56	final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics
39	dl	1.54
40			/**
41	dl	1.79	* Full nonpublic constructor.
42	jsr166	1.1	*/
43	dl	1.79	ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool,
44			boolean useSystemClassLoader, boolean isInnocuous) {
45			super(group, null, pool.nextWorkerThreadName(), 0L);
46			UncaughtExceptionHandler handler = (this.pool = pool).ueh;
47			this.workQueue = new ForkJoinPool.WorkQueue(this, isInnocuous);
48			super.setDaemon(true);
49			if (handler != null)
50			super.setUncaughtExceptionHandler(handler);
51			if (useSystemClassLoader)
52			super.setContextClassLoader(ClassLoader.getSystemClassLoader());
53	dl	1.14	}
54
55	jsr166	1.1	/**
56	dl	1.79	* Creates a ForkJoinWorkerThread operating in the given thread group and
57			* pool.
58			*
59			* @param group if non-null, the thread group for this thread
60			* @param pool the pool this thread works in
61			* @throws NullPointerException if pool is null
62	jsr166	1.74	*/
63	jsr166	1.82	/* TODO: protected */ ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool) {
64	dl	1.79	this(group, pool, false, false);
65	jsr166	1.74	}
66
67			/**
68	dl	1.79	* Creates a ForkJoinWorkerThread operating in the given pool.
69			*
70			* @param pool the pool this thread works in
71			* @throws NullPointerException if pool is null
72	dl	1.60	*/
73	dl	1.79	protected ForkJoinWorkerThread(ForkJoinPool pool) {
74			this(null, pool, false, false);
75	dl	1.60	}
76
77			/**
78	jsr166	1.1	* Returns the pool hosting this thread.
79			*
80			* @return the pool
81			*/
82			public ForkJoinPool getPool() {
83			return pool;
84			}
85
86			/**
87	jsr166	1.59	* Returns the unique index number of this thread in its pool.
88			* The returned value ranges from zero to the maximum number of
89			* threads (minus one) that may exist in the pool, and does not
90			* change during the lifetime of the thread. This method may be
91			* useful for applications that track status or collect results
92			* per-worker-thread rather than per-task.
93	jsr166	1.1	*
94			* @return the index number
95			*/
96			public int getPoolIndex() {
97	dl	1.65	return workQueue.getPoolIndex();
98	dl	1.45	}
99
100	jsr166	1.1	/**
101	dl	1.14	* Initializes internal state after construction but before
102			* processing any tasks. If you override this method, you must
103	jsr166	1.39	* invoke {@code super.onStart()} at the beginning of the method.
104	dl	1.14	* Initialization requires care: Most fields must have legal
105			* default values, to ensure that attempted accesses from other
106			* threads work correctly even before this thread starts
107			* processing tasks.
108	jsr166	1.1	*/
109	dl	1.14	protected void onStart() {
110			}
111	jsr166	1.1
112			/**
113	dl	1.14	* Performs cleanup associated with termination of this worker
114			* thread. If you override this method, you must invoke
115			* {@code super.onTermination} at the end of the overridden method.
116	jsr166	1.4	*
117	dl	1.14	* @param exception the exception causing this thread to abort due
118			* to an unrecoverable error, or {@code null} if completed normally
119	jsr166	1.1	*/
120	dl	1.14	protected void onTermination(Throwable exception) {
121	jsr166	1.1	}
122
123			/**
124			* This method is required to be public, but should never be
125			* called explicitly. It performs the main run loop to execute
126	jsr166	1.40	* {@link ForkJoinTask}s.
127	jsr166	1.1	*/
128			public void run() {
129	dl	1.79	Throwable exception = null;
130			ForkJoinPool p = pool;
131			ForkJoinPool.WorkQueue w = workQueue;
132			if (p != null && w != null) { // skip on failed initialization
133	dl	1.52	try {
134	dl	1.79	p.registerWorker(w);
135	dl	1.60	onStart();
136	dl	1.79	p.runWorker(w);
137	dl	1.52	} catch (Throwable ex) {
138	dl	1.60	exception = ex;
139	dl	1.52	} finally {
140	dl	1.60	try {
141			onTermination(exception);
142			} catch (Throwable ex) {
143			if (exception == null)
144			exception = ex;
145			} finally {
146	dl	1.79	p.deregisterWorker(this, exception);
147	dl	1.60	}
148			}
149			}
150			}
151
152			/**
153			* A worker thread that has no permissions, is not a member of any
154	jsr166	1.74	* user-defined ThreadGroup, uses the system class loader as
155			* thread context class loader, and erases all ThreadLocals after
156	dl	1.60	* running each top-level task.
157			*/
158			static final class InnocuousForkJoinWorkerThread extends ForkJoinWorkerThread {
159			/** The ThreadGroup for all InnocuousForkJoinWorkerThreads */
160			private static final ThreadGroup innocuousThreadGroup =
161	jsr166	1.75	AccessController.doPrivileged(new PrivilegedAction<>() {
162			public ThreadGroup run() {
163			ThreadGroup group = Thread.currentThread().getThreadGroup();
164			for (ThreadGroup p; (p = group.getParent()) != null; )
165			group = p;
166			return new ThreadGroup(
167			group, "InnocuousForkJoinWorkerThreadGroup");
168			}});
169	dl	1.60
170			InnocuousForkJoinWorkerThread(ForkJoinPool pool) {
171	dl	1.79	super(innocuousThreadGroup, pool, true, true);
172	dl	1.60	}
173
174			@Override // to silently fail
175			public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { }
176
177			@Override // paranoically
178			public void setContextClassLoader(ClassLoader cl) {
179	dl	1.78	if (cl != null && ClassLoader.getSystemClassLoader() != cl)
180	dl	1.77	throw new SecurityException("setContextClassLoader");
181	dl	1.60	}
182	jsr166	1.1	}
183			}