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;
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:	1.80
Committed:	Tue Aug 11 20:56:30 2020 UTC (3 years, 9 months ago) by jsr166
Branch:	MAIN
Changes since 1.79:	+0 -1 lines
Log Message:	fix errorprone [RemoveUnusedImports]
#	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.AccessController;
10	import java.security.PrivilegedAction;
11	import java.security.ProtectionDomain;
12
13	/**
14	* A thread managed by a {@link ForkJoinPool}, which executes
15	* {@link ForkJoinTask}s.
16	* This class is subclassable solely for the sake of adding
17	* functionality -- there are no overridable methods dealing with
18	* scheduling or execution. However, you can override initialization
19	* and termination methods surrounding the main task processing loop.
20	* If you do create such a subclass, you will also need to supply a
21	* custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to
22	* {@linkplain ForkJoinPool#ForkJoinPool(int, ForkJoinWorkerThreadFactory,
23	* UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)
24	* use it} in a {@code ForkJoinPool}.
25	*
26	* @since 1.7
27	* @author Doug Lea
28	*/
29	public class ForkJoinWorkerThread extends Thread {
30	/*
31	* ForkJoinWorkerThreads are managed by ForkJoinPools and perform
32	* ForkJoinTasks. For explanation, see the internal documentation
33	* of class ForkJoinPool.
34	*
35	* This class just maintains links to its pool and WorkQueue.
36	*/
37
38	final ForkJoinPool pool; // the pool this thread works in
39	final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics
40
41	/**
42	* Full nonpublic constructor.
43	*/
44	ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool,
45	boolean useSystemClassLoader, boolean isInnocuous) {
46	super(group, null, pool.nextWorkerThreadName(), 0L);
47	UncaughtExceptionHandler handler = (this.pool = pool).ueh;
48	this.workQueue = new ForkJoinPool.WorkQueue(this, isInnocuous);
49	super.setDaemon(true);
50	if (handler != null)
51	super.setUncaughtExceptionHandler(handler);
52	if (useSystemClassLoader)
53	super.setContextClassLoader(ClassLoader.getSystemClassLoader());
54	}
55
56	/**
57	* Creates a ForkJoinWorkerThread operating in the given thread group and
58	* pool.
59	*
60	* @param group if non-null, the thread group for this thread
61	* @param pool the pool this thread works in
62	* @throws NullPointerException if pool is null
63	*/
64	protected ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool) {
65	this(group, pool, false, false);
66	}
67
68	/**
69	* Creates a ForkJoinWorkerThread operating in the given pool.
70	*
71	* @param pool the pool this thread works in
72	* @throws NullPointerException if pool is null
73	*/
74	protected ForkJoinWorkerThread(ForkJoinPool pool) {
75	this(null, pool, false, false);
76	}
77
78	/**
79	* Returns the pool hosting this thread.
80	*
81	* @return the pool
82	*/
83	public ForkJoinPool getPool() {
84	return pool;
85	}
86
87	/**
88	* Returns the unique index number of this thread in its pool.
89	* The returned value ranges from zero to the maximum number of
90	* threads (minus one) that may exist in the pool, and does not
91	* change during the lifetime of the thread. This method may be
92	* useful for applications that track status or collect results
93	* per-worker-thread rather than per-task.
94	*
95	* @return the index number
96	*/
97	public int getPoolIndex() {
98	return workQueue.getPoolIndex();
99	}
100
101	/**
102	* Initializes internal state after construction but before
103	* processing any tasks. If you override this method, you must
104	* invoke {@code super.onStart()} at the beginning of the method.
105	* Initialization requires care: Most fields must have legal
106	* default values, to ensure that attempted accesses from other
107	* threads work correctly even before this thread starts
108	* processing tasks.
109	*/
110	protected void onStart() {
111	}
112
113	/**
114	* Performs cleanup associated with termination of this worker
115	* thread. If you override this method, you must invoke
116	* {@code super.onTermination} at the end of the overridden method.
117	*
118	* @param exception the exception causing this thread to abort due
119	* to an unrecoverable error, or {@code null} if completed normally
120	*/
121	protected void onTermination(Throwable exception) {
122	}
123
124	/**
125	* This method is required to be public, but should never be
126	* called explicitly. It performs the main run loop to execute
127	* {@link ForkJoinTask}s.
128	*/
129	public void run() {
130	Throwable exception = null;
131	ForkJoinPool p = pool;
132	ForkJoinPool.WorkQueue w = workQueue;
133	if (p != null && w != null) { // skip on failed initialization
134	try {
135	p.registerWorker(w);
136	onStart();
137	p.runWorker(w);
138	} catch (Throwable ex) {
139	exception = ex;
140	} finally {
141	try {
142	onTermination(exception);
143	} catch (Throwable ex) {
144	if (exception == null)
145	exception = ex;
146	} finally {
147	p.deregisterWorker(this, exception);
148	}
149	}
150	}
151	}
152
153	/**
154	* A worker thread that has no permissions, is not a member of any
155	* user-defined ThreadGroup, uses the system class loader as
156	* thread context class loader, and erases all ThreadLocals after
157	* running each top-level task.
158	*/
159	static final class InnocuousForkJoinWorkerThread extends ForkJoinWorkerThread {
160	/** The ThreadGroup for all InnocuousForkJoinWorkerThreads */
161	private static final ThreadGroup innocuousThreadGroup =
162	AccessController.doPrivileged(new PrivilegedAction<>() {
163	public ThreadGroup run() {
164	ThreadGroup group = Thread.currentThread().getThreadGroup();
165	for (ThreadGroup p; (p = group.getParent()) != null; )
166	group = p;
167	return new ThreadGroup(
168	group, "InnocuousForkJoinWorkerThreadGroup");
169	}});
170
171	InnocuousForkJoinWorkerThread(ForkJoinPool pool) {
172	super(innocuousThreadGroup, pool, true, true);
173	}
174
175	@Override // to silently fail
176	public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { }
177
178	@Override // paranoically
179	public void setContextClassLoader(ClassLoader cl) {
180	if (cl != null && ClassLoader.getSystemClassLoader() != cl)
181	throw new SecurityException("setContextClassLoader");
182	}
183	}
184	}