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 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.
     *
     * Support for (non-public) subclass InnocuousForkJoinWorkerThread
     * requires that we break quite a lot of encapsulation (via helper
     * methods in ThreadLocalRandom) both here and in the subclass to
     * access and set Thread fields.
     */

    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);
    }

    /**
     * Version for use by the default pool.  Supports setting the
     * context class loader.  This is a separate constructor to avoid
     * affecting the protected constructor.
     */
    ForkJoinWorkerThread(ForkJoinPool pool, ClassLoader ccl) {
        super("aForkJoinWorkerThread");
        super.setContextClassLoader(ccl);
        this.pool = pool;
        this.workQueue = pool.registerWorker(this);
    }

    /**
     * Version for InnocuousForkJoinWorkerThread.
     */
    ForkJoinWorkerThread(ForkJoinPool pool,
                         ClassLoader ccl,
                         ThreadGroup threadGroup,
                         AccessControlContext acc) {
        super(threadGroup, null, "aForkJoinWorkerThread");
        super.setContextClassLoader(ccl);
        ThreadLocalRandom.setInheritedAccessControlContext(this, acc);
        ThreadLocalRandom.eraseThreadLocals(this); // clear before registering
        this.pool = pool;
        this.workQueue = pool.registerWorker(this);
    }

    /**
     * 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() {
        if (workQueue.array == null) { // only run once
            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);
                }
            }
        }
    }

    /**
     * Non-public hook method for InnocuousForkJoinWorkerThread.
     */
    void afterTopLevelExec() {
    }

    /**
     * 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");
                }});

        /** An AccessControlContext supporting no privileges */
        private static final AccessControlContext INNOCUOUS_ACC =
            new AccessControlContext(
                new ProtectionDomain[] { new ProtectionDomain(null, null) });

        InnocuousForkJoinWorkerThread(ForkJoinPool pool) {
            super(pool,
                  ClassLoader.getSystemClassLoader(),
                  innocuousThreadGroup,
                  INNOCUOUS_ACC);
        }

        @Override // to erase ThreadLocals
        void afterTopLevelExec() {
            ThreadLocalRandom.eraseThreadLocals(this);
        }

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

        @Override // paranoically
        public void setContextClassLoader(ClassLoader cl) {
            throw new SecurityException("setContextClassLoader");
        }
    }
}
Revision:	1.75
Committed:	Sat Mar 18 16:32:29 2017 UTC (7 years, 2 months ago) by jsr166
Branch:	MAIN
Changes since 1.74:	+9 -11 lines
Log Message:	coding style
#	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	dl	1.60	import java.security.AccessControlContext;
10	jsr166	1.74	import java.security.AccessController;
11			import java.security.PrivilegedAction;
12	dl	1.60	import java.security.ProtectionDomain;
13
14	jsr166	1.1	/**
15	jsr166	1.40	* 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	jsr166	1.57	* custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to
23			* {@linkplain ForkJoinPool#ForkJoinPool 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			* This class just maintains links to its pool and WorkQueue. The
35	dl	1.56	* pool field is set immediately upon construction, but the
36			* workQueue field is not set until a call to registerWorker
37			* completes. This leads to a visibility race, that is tolerated
38			* by requiring that the workQueue field is only accessed by the
39			* owning thread.
40	dl	1.60	*
41			* Support for (non-public) subclass InnocuousForkJoinWorkerThread
42	dl	1.70	* requires that we break quite a lot of encapsulation (via helper
43	jsr166	1.72	* methods in ThreadLocalRandom) both here and in the subclass to
44	dl	1.70	* access and set Thread fields.
45	jsr166	1.1	*/
46
47	dl	1.52	final ForkJoinPool pool; // the pool this thread works in
48	dl	1.56	final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics
49	dl	1.54
50			/**
51	jsr166	1.1	* Creates a ForkJoinWorkerThread operating in the given pool.
52			*
53			* @param pool the pool this thread works in
54			* @throws NullPointerException if pool is null
55			*/
56			protected ForkJoinWorkerThread(ForkJoinPool pool) {
57	dl	1.56	// Use a placeholder until a useful name can be set in registerWorker
58			super("aForkJoinWorkerThread");
59	dl	1.55	this.pool = pool;
60	dl	1.56	this.workQueue = pool.registerWorker(this);
61	dl	1.14	}
62
63	jsr166	1.1	/**
64	jsr166	1.74	* Version for use by the default pool. Supports setting the
65			* context class loader. This is a separate constructor to avoid
66			* affecting the protected constructor.
67			*/
68			ForkJoinWorkerThread(ForkJoinPool pool, ClassLoader ccl) {
69			super("aForkJoinWorkerThread");
70			super.setContextClassLoader(ccl);
71			this.pool = pool;
72			this.workQueue = pool.registerWorker(this);
73			}
74
75			/**
76	jsr166	1.68	* Version for InnocuousForkJoinWorkerThread.
77	dl	1.60	*/
78	jsr166	1.74	ForkJoinWorkerThread(ForkJoinPool pool,
79			ClassLoader ccl,
80			ThreadGroup threadGroup,
81	dl	1.60	AccessControlContext acc) {
82			super(threadGroup, null, "aForkJoinWorkerThread");
83	jsr166	1.74	super.setContextClassLoader(ccl);
84	jsr166	1.71	ThreadLocalRandom.setInheritedAccessControlContext(this, acc);
85	dl	1.70	ThreadLocalRandom.eraseThreadLocals(this); // clear before registering
86	dl	1.60	this.pool = pool;
87			this.workQueue = pool.registerWorker(this);
88			}
89
90			/**
91	jsr166	1.1	* Returns the pool hosting this thread.
92			*
93			* @return the pool
94			*/
95			public ForkJoinPool getPool() {
96			return pool;
97			}
98
99			/**
100	jsr166	1.59	* Returns the unique index number of this thread in its pool.
101			* The returned value ranges from zero to the maximum number of
102			* threads (minus one) that may exist in the pool, and does not
103			* change during the lifetime of the thread. This method may be
104			* useful for applications that track status or collect results
105			* per-worker-thread rather than per-task.
106	jsr166	1.1	*
107			* @return the index number
108			*/
109			public int getPoolIndex() {
110	dl	1.65	return workQueue.getPoolIndex();
111	dl	1.45	}
112
113	jsr166	1.1	/**
114	dl	1.14	* Initializes internal state after construction but before
115			* processing any tasks. If you override this method, you must
116	jsr166	1.39	* invoke {@code super.onStart()} at the beginning of the method.
117	dl	1.14	* Initialization requires care: Most fields must have legal
118			* default values, to ensure that attempted accesses from other
119			* threads work correctly even before this thread starts
120			* processing tasks.
121	jsr166	1.1	*/
122	dl	1.14	protected void onStart() {
123			}
124	jsr166	1.1
125			/**
126	dl	1.14	* Performs cleanup associated with termination of this worker
127			* thread. If you override this method, you must invoke
128			* {@code super.onTermination} at the end of the overridden method.
129	jsr166	1.4	*
130	dl	1.14	* @param exception the exception causing this thread to abort due
131			* to an unrecoverable error, or {@code null} if completed normally
132	jsr166	1.1	*/
133	dl	1.14	protected void onTermination(Throwable exception) {
134	jsr166	1.1	}
135
136			/**
137			* This method is required to be public, but should never be
138			* called explicitly. It performs the main run loop to execute
139	jsr166	1.40	* {@link ForkJoinTask}s.
140	jsr166	1.1	*/
141			public void run() {
142	dl	1.60	if (workQueue.array == null) { // only run once
143			Throwable exception = null;
144	dl	1.52	try {
145	dl	1.60	onStart();
146			pool.runWorker(workQueue);
147	dl	1.52	} catch (Throwable ex) {
148	dl	1.60	exception = ex;
149	dl	1.52	} finally {
150	dl	1.60	try {
151			onTermination(exception);
152			} catch (Throwable ex) {
153			if (exception == null)
154			exception = ex;
155			} finally {
156			pool.deregisterWorker(this, exception);
157			}
158			}
159			}
160			}
161
162			/**
163	jsr166	1.68	* Non-public hook method for InnocuousForkJoinWorkerThread.
164	dl	1.60	*/
165			void afterTopLevelExec() {
166			}
167
168			/**
169			* A worker thread that has no permissions, is not a member of any
170	jsr166	1.74	* user-defined ThreadGroup, uses the system class loader as
171			* thread context class loader, and erases all ThreadLocals after
172	dl	1.60	* running each top-level task.
173			*/
174			static final class InnocuousForkJoinWorkerThread extends ForkJoinWorkerThread {
175			/** The ThreadGroup for all InnocuousForkJoinWorkerThreads */
176			private static final ThreadGroup innocuousThreadGroup =
177	jsr166	1.75	AccessController.doPrivileged(new PrivilegedAction<>() {
178			public ThreadGroup run() {
179			ThreadGroup group = Thread.currentThread().getThreadGroup();
180			for (ThreadGroup p; (p = group.getParent()) != null; )
181			group = p;
182			return new ThreadGroup(
183			group, "InnocuousForkJoinWorkerThreadGroup");
184			}});
185	dl	1.60
186			/** An AccessControlContext supporting no privileges */
187			private static final AccessControlContext INNOCUOUS_ACC =
188			new AccessControlContext(
189	jsr166	1.75	new ProtectionDomain[] { new ProtectionDomain(null, null) });
190	dl	1.60
191			InnocuousForkJoinWorkerThread(ForkJoinPool pool) {
192	jsr166	1.74	super(pool,
193			ClassLoader.getSystemClassLoader(),
194			innocuousThreadGroup,
195			INNOCUOUS_ACC);
196	dl	1.60	}
197
198			@Override // to erase ThreadLocals
199			void afterTopLevelExec() {
200	dl	1.70	ThreadLocalRandom.eraseThreadLocals(this);
201	dl	1.60	}
202
203			@Override // to silently fail
204			public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { }
205
206			@Override // paranoically
207			public void setContextClassLoader(ClassLoader cl) {
208			throw new SecurityException("setContextClassLoader");
209			}
210	jsr166	1.1	}
211			}