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.  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) {
            if (cl != null && !ClassLoader.getSystemClassLoader().equals(cl))
                throw new SecurityException("setContextClassLoader");
        }
    }
}
Revision:	1.77
Committed:	Thu Dec 13 14:17:33 2018 UTC (5 years, 5 months ago) by dl
Branch:	MAIN
Changes since 1.76:	+2 -1 lines
Log Message:	don't throw needless exception in InnocuousForkJoinWorkerThread.setContextClassLoader
#	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	jsr166	1.76	* {@linkplain ForkJoinPool#ForkJoinPool(int, ForkJoinWorkerThreadFactory,
24			* UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)
25			* use it} in a {@code ForkJoinPool}.
26	jsr166	1.1	*
27			* @since 1.7
28			* @author Doug Lea
29			*/
30			public class ForkJoinWorkerThread extends Thread {
31			/*
32	dl	1.14	* ForkJoinWorkerThreads are managed by ForkJoinPools and perform
33	dl	1.52	* ForkJoinTasks. For explanation, see the internal documentation
34			* of class ForkJoinPool.
35	dl	1.55	*
36			* This class just maintains links to its pool and WorkQueue. The
37	dl	1.56	* pool field is set immediately upon construction, but the
38			* workQueue field is not set until a call to registerWorker
39			* completes. This leads to a visibility race, that is tolerated
40			* by requiring that the workQueue field is only accessed by the
41			* owning thread.
42	dl	1.60	*
43			* Support for (non-public) subclass InnocuousForkJoinWorkerThread
44	dl	1.70	* requires that we break quite a lot of encapsulation (via helper
45	jsr166	1.72	* methods in ThreadLocalRandom) both here and in the subclass to
46	dl	1.70	* access and set Thread fields.
47	jsr166	1.1	*/
48
49	dl	1.52	final ForkJoinPool pool; // the pool this thread works in
50	dl	1.56	final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics
51	dl	1.54
52			/**
53	jsr166	1.1	* Creates a ForkJoinWorkerThread operating in the given pool.
54			*
55			* @param pool the pool this thread works in
56			* @throws NullPointerException if pool is null
57			*/
58			protected ForkJoinWorkerThread(ForkJoinPool pool) {
59	dl	1.56	// Use a placeholder until a useful name can be set in registerWorker
60			super("aForkJoinWorkerThread");
61	dl	1.55	this.pool = pool;
62	dl	1.56	this.workQueue = pool.registerWorker(this);
63	dl	1.14	}
64
65	jsr166	1.1	/**
66	jsr166	1.74	* Version for use by the default pool. Supports setting the
67			* context class loader. This is a separate constructor to avoid
68			* affecting the protected constructor.
69			*/
70			ForkJoinWorkerThread(ForkJoinPool pool, ClassLoader ccl) {
71			super("aForkJoinWorkerThread");
72			super.setContextClassLoader(ccl);
73			this.pool = pool;
74			this.workQueue = pool.registerWorker(this);
75			}
76
77			/**
78	jsr166	1.68	* Version for InnocuousForkJoinWorkerThread.
79	dl	1.60	*/
80	jsr166	1.74	ForkJoinWorkerThread(ForkJoinPool pool,
81			ClassLoader ccl,
82			ThreadGroup threadGroup,
83	dl	1.60	AccessControlContext acc) {
84			super(threadGroup, null, "aForkJoinWorkerThread");
85	jsr166	1.74	super.setContextClassLoader(ccl);
86	jsr166	1.71	ThreadLocalRandom.setInheritedAccessControlContext(this, acc);
87	dl	1.70	ThreadLocalRandom.eraseThreadLocals(this); // clear before registering
88	dl	1.60	this.pool = pool;
89			this.workQueue = pool.registerWorker(this);
90			}
91
92			/**
93	jsr166	1.1	* Returns the pool hosting this thread.
94			*
95			* @return the pool
96			*/
97			public ForkJoinPool getPool() {
98			return pool;
99			}
100
101			/**
102	jsr166	1.59	* Returns the unique index number of this thread in its pool.
103			* The returned value ranges from zero to the maximum number of
104			* threads (minus one) that may exist in the pool, and does not
105			* change during the lifetime of the thread. This method may be
106			* useful for applications that track status or collect results
107			* per-worker-thread rather than per-task.
108	jsr166	1.1	*
109			* @return the index number
110			*/
111			public int getPoolIndex() {
112	dl	1.65	return workQueue.getPoolIndex();
113	dl	1.45	}
114
115	jsr166	1.1	/**
116	dl	1.14	* Initializes internal state after construction but before
117			* processing any tasks. If you override this method, you must
118	jsr166	1.39	* invoke {@code super.onStart()} at the beginning of the method.
119	dl	1.14	* Initialization requires care: Most fields must have legal
120			* default values, to ensure that attempted accesses from other
121			* threads work correctly even before this thread starts
122			* processing tasks.
123	jsr166	1.1	*/
124	dl	1.14	protected void onStart() {
125			}
126	jsr166	1.1
127			/**
128	dl	1.14	* Performs cleanup associated with termination of this worker
129			* thread. If you override this method, you must invoke
130			* {@code super.onTermination} at the end of the overridden method.
131	jsr166	1.4	*
132	dl	1.14	* @param exception the exception causing this thread to abort due
133			* to an unrecoverable error, or {@code null} if completed normally
134	jsr166	1.1	*/
135	dl	1.14	protected void onTermination(Throwable exception) {
136	jsr166	1.1	}
137
138			/**
139			* This method is required to be public, but should never be
140			* called explicitly. It performs the main run loop to execute
141	jsr166	1.40	* {@link ForkJoinTask}s.
142	jsr166	1.1	*/
143			public void run() {
144	dl	1.60	if (workQueue.array == null) { // only run once
145			Throwable exception = null;
146	dl	1.52	try {
147	dl	1.60	onStart();
148			pool.runWorker(workQueue);
149	dl	1.52	} catch (Throwable ex) {
150	dl	1.60	exception = ex;
151	dl	1.52	} finally {
152	dl	1.60	try {
153			onTermination(exception);
154			} catch (Throwable ex) {
155			if (exception == null)
156			exception = ex;
157			} finally {
158			pool.deregisterWorker(this, exception);
159			}
160			}
161			}
162			}
163
164			/**
165	jsr166	1.68	* Non-public hook method for InnocuousForkJoinWorkerThread.
166	dl	1.60	*/
167			void afterTopLevelExec() {
168			}
169
170			/**
171			* A worker thread that has no permissions, is not a member of any
172	jsr166	1.74	* user-defined ThreadGroup, uses the system class loader as
173			* thread context class loader, and erases all ThreadLocals after
174	dl	1.60	* running each top-level task.
175			*/
176			static final class InnocuousForkJoinWorkerThread extends ForkJoinWorkerThread {
177			/** The ThreadGroup for all InnocuousForkJoinWorkerThreads */
178			private static final ThreadGroup innocuousThreadGroup =
179	jsr166	1.75	AccessController.doPrivileged(new PrivilegedAction<>() {
180			public ThreadGroup run() {
181			ThreadGroup group = Thread.currentThread().getThreadGroup();
182			for (ThreadGroup p; (p = group.getParent()) != null; )
183			group = p;
184			return new ThreadGroup(
185			group, "InnocuousForkJoinWorkerThreadGroup");
186			}});
187	dl	1.60
188			/** An AccessControlContext supporting no privileges */
189			private static final AccessControlContext INNOCUOUS_ACC =
190			new AccessControlContext(
191	jsr166	1.75	new ProtectionDomain[] { new ProtectionDomain(null, null) });
192	dl	1.60
193			InnocuousForkJoinWorkerThread(ForkJoinPool pool) {
194	jsr166	1.74	super(pool,
195			ClassLoader.getSystemClassLoader(),
196			innocuousThreadGroup,
197			INNOCUOUS_ACC);
198	dl	1.60	}
199
200			@Override // to erase ThreadLocals
201			void afterTopLevelExec() {
202	dl	1.70	ThreadLocalRandom.eraseThreadLocals(this);
203	dl	1.60	}
204
205			@Override // to silently fail
206			public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { }
207
208			@Override // paranoically
209			public void setContextClassLoader(ClassLoader cl) {
210	dl	1.77	if (cl != null && !ClassLoader.getSystemClassLoader().equals(cl))
211			throw new SecurityException("setContextClassLoader");
212	dl	1.60	}
213	jsr166	1.1	}
214			}