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
#	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. The
37	* 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	*
43	* Support for (non-public) subclass InnocuousForkJoinWorkerThread
44	* requires that we break quite a lot of encapsulation (via helper
45	* methods in ThreadLocalRandom) both here and in the subclass to
46	* access and set Thread fields.
47	*/
48
49	final ForkJoinPool pool; // the pool this thread works in
50	final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics
51
52	/**
53	* 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	// Use a placeholder until a useful name can be set in registerWorker
60	super("aForkJoinWorkerThread");
61	this.pool = pool;
62	this.workQueue = pool.registerWorker(this);
63	}
64
65	/**
66	* 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	* Version for InnocuousForkJoinWorkerThread.
79	*/
80	ForkJoinWorkerThread(ForkJoinPool pool,
81	ClassLoader ccl,
82	ThreadGroup threadGroup,
83	AccessControlContext acc) {
84	super(threadGroup, null, "aForkJoinWorkerThread");
85	super.setContextClassLoader(ccl);
86	ThreadLocalRandom.setInheritedAccessControlContext(this, acc);
87	ThreadLocalRandom.eraseThreadLocals(this); // clear before registering
88	this.pool = pool;
89	this.workQueue = pool.registerWorker(this);
90	}
91
92	/**
93	* Returns the pool hosting this thread.
94	*
95	* @return the pool
96	*/
97	public ForkJoinPool getPool() {
98	return pool;
99	}
100
101	/**
102	* 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	*
109	* @return the index number
110	*/
111	public int getPoolIndex() {
112	return workQueue.getPoolIndex();
113	}
114
115	/**
116	* Initializes internal state after construction but before
117	* processing any tasks. If you override this method, you must
118	* invoke {@code super.onStart()} at the beginning of the method.
119	* 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	*/
124	protected void onStart() {
125	}
126
127	/**
128	* 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	*
132	* @param exception the exception causing this thread to abort due
133	* to an unrecoverable error, or {@code null} if completed normally
134	*/
135	protected void onTermination(Throwable exception) {
136	}
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	* {@link ForkJoinTask}s.
142	*/
143	public void run() {
144	if (workQueue.array == null) { // only run once
145	Throwable exception = null;
146	try {
147	onStart();
148	pool.runWorker(workQueue);
149	} catch (Throwable ex) {
150	exception = ex;
151	} finally {
152	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	* Non-public hook method for InnocuousForkJoinWorkerThread.
166	*/
167	void afterTopLevelExec() {
168	}
169
170	/**
171	* A worker thread that has no permissions, is not a member of any
172	* user-defined ThreadGroup, uses the system class loader as
173	* thread context class loader, and erases all ThreadLocals after
174	* 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	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
188	/** An AccessControlContext supporting no privileges */
189	private static final AccessControlContext INNOCUOUS_ACC =
190	new AccessControlContext(
191	new ProtectionDomain[] { new ProtectionDomain(null, null) });
192
193	InnocuousForkJoinWorkerThread(ForkJoinPool pool) {
194	super(pool,
195	ClassLoader.getSystemClassLoader(),
196	innocuousThreadGroup,
197	INNOCUOUS_ACC);
198	}
199
200	@Override // to erase ThreadLocals
201	void afterTopLevelExec() {
202	ThreadLocalRandom.eraseThreadLocals(this);
203	}
204
205	@Override // to silently fail
206	public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { }
207
208	@Override // paranoically
209	public void setContextClassLoader(ClassLoader cl) {
210	if (cl != null && !ClassLoader.getSystemClassLoader().equals(cl))
211	throw new SecurityException("setContextClassLoader");
212	}
213	}
214	}