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.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.ProtectionDomain;

/**
 * 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
     */
    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:	1.79
Committed:	Fri Jan 17 18:12:07 2020 UTC (4 years, 4 months ago) by dl
Branch:	MAIN
Changes since 1.78:	+34 -63 lines
Log Message:	FJ 1/20 refresh
#	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 java.util.concurrent;
8
9	import java.security.AccessControlContext;
10	import java.security.AccessController;
11	import java.security.PrivilegedAction;
12	import java.security.ProtectionDomain;
13
14	/**
15	* A thread managed by a {@link ForkJoinPool}, which executes
16	* {@link ForkJoinTask}s.
17	* This class is subclassable solely for the sake of adding
18	* functionality -- there are no overridable methods dealing with
19	* scheduling or execution. However, you can override initialization
20	* and termination methods surrounding the main task processing loop.
21	* If you do create such a subclass, you will also need to supply a
22	* custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to
23	* {@linkplain ForkJoinPool#ForkJoinPool(int, ForkJoinWorkerThreadFactory,
24	* UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)
25	* use it} in a {@code ForkJoinPool}.
26	*
27	* @since 1.7
28	* @author Doug Lea
29	*/
30	public class ForkJoinWorkerThread extends Thread {
31	/*
32	* ForkJoinWorkerThreads are managed by ForkJoinPools and perform
33	* ForkJoinTasks. For explanation, see the internal documentation
34	* of class ForkJoinPool.
35	*
36	* This class just maintains links to its pool and WorkQueue.
37	*/
38
39	final ForkJoinPool pool; // the pool this thread works in
40	final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics
41
42	/**
43	* Full nonpublic constructor.
44	*/
45	ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool,
46	boolean useSystemClassLoader, boolean isInnocuous) {
47	super(group, null, pool.nextWorkerThreadName(), 0L);
48	UncaughtExceptionHandler handler = (this.pool = pool).ueh;
49	this.workQueue = new ForkJoinPool.WorkQueue(this, isInnocuous);
50	super.setDaemon(true);
51	if (handler != null)
52	super.setUncaughtExceptionHandler(handler);
53	if (useSystemClassLoader)
54	super.setContextClassLoader(ClassLoader.getSystemClassLoader());
55	}
56
57	/**
58	* Creates a ForkJoinWorkerThread operating in the given thread group and
59	* pool.
60	*
61	* @param group if non-null, the thread group for this thread
62	* @param pool the pool this thread works in
63	* @throws NullPointerException if pool is null
64	*/
65	protected ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool) {
66	this(group, pool, false, false);
67	}
68
69	/**
70	* Creates a ForkJoinWorkerThread operating in the given pool.
71	*
72	* @param pool the pool this thread works in
73	* @throws NullPointerException if pool is null
74	*/
75	protected ForkJoinWorkerThread(ForkJoinPool pool) {
76	this(null, pool, false, false);
77	}
78
79	/**
80	* Returns the pool hosting this thread.
81	*
82	* @return the pool
83	*/
84	public ForkJoinPool getPool() {
85	return pool;
86	}
87
88	/**
89	* Returns the unique index number of this thread in its pool.
90	* The returned value ranges from zero to the maximum number of
91	* threads (minus one) that may exist in the pool, and does not
92	* change during the lifetime of the thread. This method may be
93	* useful for applications that track status or collect results
94	* per-worker-thread rather than per-task.
95	*
96	* @return the index number
97	*/
98	public int getPoolIndex() {
99	return workQueue.getPoolIndex();
100	}
101
102	/**
103	* Initializes internal state after construction but before
104	* processing any tasks. If you override this method, you must
105	* invoke {@code super.onStart()} at the beginning of the method.
106	* Initialization requires care: Most fields must have legal
107	* default values, to ensure that attempted accesses from other
108	* threads work correctly even before this thread starts
109	* processing tasks.
110	*/
111	protected void onStart() {
112	}
113
114	/**
115	* Performs cleanup associated with termination of this worker
116	* thread. If you override this method, you must invoke
117	* {@code super.onTermination} at the end of the overridden method.
118	*
119	* @param exception the exception causing this thread to abort due
120	* to an unrecoverable error, or {@code null} if completed normally
121	*/
122	protected void onTermination(Throwable exception) {
123	}
124
125	/**
126	* This method is required to be public, but should never be
127	* called explicitly. It performs the main run loop to execute
128	* {@link ForkJoinTask}s.
129	*/
130	public void run() {
131	Throwable exception = null;
132	ForkJoinPool p = pool;
133	ForkJoinPool.WorkQueue w = workQueue;
134	if (p != null && w != null) { // skip on failed initialization
135	try {
136	p.registerWorker(w);
137	onStart();
138	p.runWorker(w);
139	} catch (Throwable ex) {
140	exception = ex;
141	} finally {
142	try {
143	onTermination(exception);
144	} catch (Throwable ex) {
145	if (exception == null)
146	exception = ex;
147	} finally {
148	p.deregisterWorker(this, exception);
149	}
150	}
151	}
152	}
153
154	/**
155	* A worker thread that has no permissions, is not a member of any
156	* user-defined ThreadGroup, uses the system class loader as
157	* thread context class loader, and erases all ThreadLocals after
158	* running each top-level task.
159	*/
160	static final class InnocuousForkJoinWorkerThread extends ForkJoinWorkerThread {
161	/** The ThreadGroup for all InnocuousForkJoinWorkerThreads */
162	private static final ThreadGroup innocuousThreadGroup =
163	AccessController.doPrivileged(new PrivilegedAction<>() {
164	public ThreadGroup run() {
165	ThreadGroup group = Thread.currentThread().getThreadGroup();
166	for (ThreadGroup p; (p = group.getParent()) != null; )
167	group = p;
168	return new ThreadGroup(
169	group, "InnocuousForkJoinWorkerThreadGroup");
170	}});
171
172	InnocuousForkJoinWorkerThread(ForkJoinPool pool) {
173	super(innocuousThreadGroup, pool, true, true);
174	}
175
176	@Override // to silently fail
177	public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { }
178
179	@Override // paranoically
180	public void setContextClassLoader(ClassLoader cl) {
181	if (cl != null && ClassLoader.getSystemClassLoader() != cl)
182	throw new SecurityException("setContextClassLoader");
183	}
184	}
185	}