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 =
            java.security.AccessController.doPrivileged(
                new java.security.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:	1.74
Committed:	Tue Jan 31 01:44:39 2017 UTC (7 years, 4 months ago) by jsr166
Branch:	MAIN
Changes since 1.73:	+32 -16 lines
Log Message:	JDK-8172726: ForkJoin common pool retains a reference to the thread context class loader
#	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 use it} in a {@code ForkJoinPool}.
24	*
25	* @since 1.7
26	* @author Doug Lea
27	*/
28	public class ForkJoinWorkerThread extends Thread {
29	/*
30	* ForkJoinWorkerThreads are managed by ForkJoinPools and perform
31	* ForkJoinTasks. For explanation, see the internal documentation
32	* of class ForkJoinPool.
33	*
34	* This class just maintains links to its pool and WorkQueue. The
35	* 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	*
41	* Support for (non-public) subclass InnocuousForkJoinWorkerThread
42	* requires that we break quite a lot of encapsulation (via helper
43	* methods in ThreadLocalRandom) both here and in the subclass to
44	* access and set Thread fields.
45	*/
46
47	final ForkJoinPool pool; // the pool this thread works in
48	final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics
49
50	/**
51	* 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	// Use a placeholder until a useful name can be set in registerWorker
58	super("aForkJoinWorkerThread");
59	this.pool = pool;
60	this.workQueue = pool.registerWorker(this);
61	}
62
63	/**
64	* 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	* Version for InnocuousForkJoinWorkerThread.
77	*/
78	ForkJoinWorkerThread(ForkJoinPool pool,
79	ClassLoader ccl,
80	ThreadGroup threadGroup,
81	AccessControlContext acc) {
82	super(threadGroup, null, "aForkJoinWorkerThread");
83	super.setContextClassLoader(ccl);
84	ThreadLocalRandom.setInheritedAccessControlContext(this, acc);
85	ThreadLocalRandom.eraseThreadLocals(this); // clear before registering
86	this.pool = pool;
87	this.workQueue = pool.registerWorker(this);
88	}
89
90	/**
91	* Returns the pool hosting this thread.
92	*
93	* @return the pool
94	*/
95	public ForkJoinPool getPool() {
96	return pool;
97	}
98
99	/**
100	* 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	*
107	* @return the index number
108	*/
109	public int getPoolIndex() {
110	return workQueue.getPoolIndex();
111	}
112
113	/**
114	* Initializes internal state after construction but before
115	* processing any tasks. If you override this method, you must
116	* invoke {@code super.onStart()} at the beginning of the method.
117	* 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	*/
122	protected void onStart() {
123	}
124
125	/**
126	* 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	*
130	* @param exception the exception causing this thread to abort due
131	* to an unrecoverable error, or {@code null} if completed normally
132	*/
133	protected void onTermination(Throwable exception) {
134	}
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	* {@link ForkJoinTask}s.
140	*/
141	public void run() {
142	if (workQueue.array == null) { // only run once
143	Throwable exception = null;
144	try {
145	onStart();
146	pool.runWorker(workQueue);
147	} catch (Throwable ex) {
148	exception = ex;
149	} finally {
150	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	* Non-public hook method for InnocuousForkJoinWorkerThread.
164	*/
165	void afterTopLevelExec() {
166	}
167
168	/**
169	* A worker thread that has no permissions, is not a member of any
170	* user-defined ThreadGroup, uses the system class loader as
171	* thread context class loader, and erases all ThreadLocals after
172	* 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	java.security.AccessController.doPrivileged(
178	new java.security.PrivilegedAction<>() {
179	public ThreadGroup run() {
180	ThreadGroup group = Thread.currentThread().getThreadGroup();
181	for (ThreadGroup p; (p = group.getParent()) != null; )
182	group = p;
183	return new ThreadGroup(group, "InnocuousForkJoinWorkerThreadGroup");
184	}});
185
186	/** An AccessControlContext supporting no privileges */
187	private static final AccessControlContext INNOCUOUS_ACC =
188	new AccessControlContext(
189	new ProtectionDomain[] {
190	new ProtectionDomain(null, null)
191	});
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	throw new SecurityException("setContextClassLoader");
211	}
212	}
213	}