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.AccessControlContext;
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, !isInnocuous);
        UncaughtExceptionHandler handler = (this.pool = pool).ueh;
        this.workQueue = new ForkJoinPool.WorkQueue(this, 0);
        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, and with the given policy for preserving ThreadLocals.
     *
     * @param group if non-null, the thread group for this thread
     * @param pool the pool this thread works in
     * @param preserveThreadLocals if true, always preserve the values of
     * ThreadLocal variables across tasks; otherwise they may be cleared.
     * @throws NullPointerException if pool is null
     * @since 19
     */
    protected ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool,
                                   boolean preserveThreadLocals) {
        this(group, pool, false, !preserveThreadLocals);
    }

    /**
     * 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;
        @SuppressWarnings("removal")
        private static final AccessControlContext innocuousACC;
        InnocuousForkJoinWorkerThread(ForkJoinPool pool) {
            super(innocuousThreadGroup, pool, true, true);
        }

        @Override @SuppressWarnings("removal")
        protected void onStart() {
            ForkJoinPool.WorkQueue w = workQueue;
            if (w != null)
                w.setInnocuous();
            Thread t = Thread.currentThread();
            ThreadLocalRandom.setInheritedAccessControlContext(t, innocuousACC);
        }

        @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");
        }

        @SuppressWarnings("removal")
        static AccessControlContext createACC() {
            return new AccessControlContext(
                new ProtectionDomain[] { new ProtectionDomain(null, null) });
        }
        static ThreadGroup createGroup() {
            ThreadGroup group = Thread.currentThread().getThreadGroup();
            for (ThreadGroup p; (p = group.getParent()) != null; )
                group = p;
            return new ThreadGroup(group, "InnocuousForkJoinWorkerThreadGroup");
        }
        static {
            @SuppressWarnings("removal")
            SecurityManager sm = System.getSecurityManager();
            @SuppressWarnings("removal")
            ThreadGroup g = innocuousThreadGroup =
                (sm == null) ? createGroup() :
                AccessController.doPrivileged(new PrivilegedAction<>() {
                        public ThreadGroup run() {
                            return createGroup(); }});
            @SuppressWarnings("removal")
            AccessControlContext a = innocuousACC =
                (sm == null) ? createACC() :
                AccessController.doPrivileged(new PrivilegedAction<>() {
                        public AccessControlContext run() {
                            return createACC(); }});
        }
    }
}
Revision:	1.84
Committed:	Fri Apr 29 17:00:36 2022 UTC (2 years, 1 month ago) by dl
Branch:	MAIN
Changes since 1.83:	+11 -8 lines
Log Message:	Misc touchups
#	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	jsr166	1.74	import java.security.AccessController;
10	dl	1.83	import java.security.AccessControlContext;
11	jsr166	1.74	import java.security.PrivilegedAction;
12	dl	1.83	import java.security.ProtectionDomain;
13	dl	1.60
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	dl	1.79	* This class just maintains links to its pool and WorkQueue.
37	jsr166	1.1	*/
38
39	dl	1.52	final ForkJoinPool pool; // the pool this thread works in
40	dl	1.56	final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics
41	dl	1.54
42			/**
43	dl	1.79	* Full nonpublic constructor.
44	jsr166	1.1	*/
45	dl	1.79	ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool,
46	dl	1.84	boolean useSystemClassLoader, boolean isInnocuous) {
47			super(group, null, pool.nextWorkerThreadName(), 0L, !isInnocuous);
48	dl	1.79	UncaughtExceptionHandler handler = (this.pool = pool).ueh;
49	dl	1.83	this.workQueue = new ForkJoinPool.WorkQueue(this, 0);
50	dl	1.79	super.setDaemon(true);
51			if (handler != null)
52			super.setUncaughtExceptionHandler(handler);
53			if (useSystemClassLoader)
54			super.setContextClassLoader(ClassLoader.getSystemClassLoader());
55	dl	1.14	}
56
57	jsr166	1.1	/**
58	dl	1.79	* Creates a ForkJoinWorkerThread operating in the given thread group and
59	dl	1.84	* pool, and with the given policy for preserving ThreadLocals.
60	dl	1.79	*
61			* @param group if non-null, the thread group for this thread
62			* @param pool the pool this thread works in
63	dl	1.84	* @param preserveThreadLocals if true, always preserve the values of
64			* ThreadLocal variables across tasks; otherwise they may be cleared.
65	dl	1.79	* @throws NullPointerException if pool is null
66	dl	1.84	* @since 19
67	jsr166	1.74	*/
68	dl	1.84	protected ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool,
69			boolean preserveThreadLocals) {
70			this(group, pool, false, !preserveThreadLocals);
71	jsr166	1.74	}
72
73			/**
74	dl	1.79	* Creates a ForkJoinWorkerThread operating in the given pool.
75			*
76			* @param pool the pool this thread works in
77			* @throws NullPointerException if pool is null
78	dl	1.60	*/
79	dl	1.79	protected ForkJoinWorkerThread(ForkJoinPool pool) {
80	dl	1.84	this(null, pool, false, false);
81	dl	1.60	}
82
83			/**
84	jsr166	1.1	* Returns the pool hosting this thread.
85			*
86			* @return the pool
87			*/
88			public ForkJoinPool getPool() {
89			return pool;
90			}
91
92			/**
93	jsr166	1.59	* Returns the unique index number of this thread in its pool.
94			* The returned value ranges from zero to the maximum number of
95			* threads (minus one) that may exist in the pool, and does not
96			* change during the lifetime of the thread. This method may be
97			* useful for applications that track status or collect results
98			* per-worker-thread rather than per-task.
99	jsr166	1.1	*
100			* @return the index number
101			*/
102			public int getPoolIndex() {
103	dl	1.65	return workQueue.getPoolIndex();
104	dl	1.45	}
105
106	jsr166	1.1	/**
107	dl	1.14	* Initializes internal state after construction but before
108			* processing any tasks. If you override this method, you must
109	jsr166	1.39	* invoke {@code super.onStart()} at the beginning of the method.
110	dl	1.14	* Initialization requires care: Most fields must have legal
111			* default values, to ensure that attempted accesses from other
112			* threads work correctly even before this thread starts
113			* processing tasks.
114	jsr166	1.1	*/
115	dl	1.14	protected void onStart() {
116			}
117	jsr166	1.1
118			/**
119	dl	1.14	* Performs cleanup associated with termination of this worker
120			* thread. If you override this method, you must invoke
121			* {@code super.onTermination} at the end of the overridden method.
122	jsr166	1.4	*
123	dl	1.14	* @param exception the exception causing this thread to abort due
124			* to an unrecoverable error, or {@code null} if completed normally
125	jsr166	1.1	*/
126	dl	1.14	protected void onTermination(Throwable exception) {
127	jsr166	1.1	}
128
129			/**
130			* This method is required to be public, but should never be
131			* called explicitly. It performs the main run loop to execute
132	jsr166	1.40	* {@link ForkJoinTask}s.
133	jsr166	1.1	*/
134			public void run() {
135	dl	1.79	Throwable exception = null;
136			ForkJoinPool p = pool;
137			ForkJoinPool.WorkQueue w = workQueue;
138			if (p != null && w != null) { // skip on failed initialization
139	dl	1.52	try {
140	dl	1.79	p.registerWorker(w);
141	dl	1.60	onStart();
142	dl	1.79	p.runWorker(w);
143	dl	1.52	} catch (Throwable ex) {
144	dl	1.60	exception = ex;
145	dl	1.52	} finally {
146	dl	1.60	try {
147			onTermination(exception);
148			} catch (Throwable ex) {
149			if (exception == null)
150			exception = ex;
151			} finally {
152	dl	1.79	p.deregisterWorker(this, exception);
153	dl	1.60	}
154			}
155			}
156			}
157
158			/**
159			* A worker thread that has no permissions, is not a member of any
160	jsr166	1.74	* user-defined ThreadGroup, uses the system class loader as
161			* thread context class loader, and erases all ThreadLocals after
162	dl	1.60	* running each top-level task.
163			*/
164			static final class InnocuousForkJoinWorkerThread extends ForkJoinWorkerThread {
165			/** The ThreadGroup for all InnocuousForkJoinWorkerThreads */
166	dl	1.83	private static final ThreadGroup innocuousThreadGroup;
167			@SuppressWarnings("removal")
168			private static final AccessControlContext innocuousACC;
169			InnocuousForkJoinWorkerThread(ForkJoinPool pool) {
170	dl	1.84	super(innocuousThreadGroup, pool, true, true);
171	dl	1.83	}
172	dl	1.60
173	dl	1.83	@Override @SuppressWarnings("removal")
174			protected void onStart() {
175			ForkJoinPool.WorkQueue w = workQueue;
176			if (w != null)
177			w.setInnocuous();
178			Thread t = Thread.currentThread();
179			ThreadLocalRandom.setInheritedAccessControlContext(t, innocuousACC);
180	dl	1.60	}
181
182			@Override // to silently fail
183			public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { }
184
185			@Override // paranoically
186			public void setContextClassLoader(ClassLoader cl) {
187	dl	1.78	if (cl != null && ClassLoader.getSystemClassLoader() != cl)
188	dl	1.77	throw new SecurityException("setContextClassLoader");
189	dl	1.60	}
190	dl	1.83
191			@SuppressWarnings("removal")
192			static AccessControlContext createACC() {
193			return new AccessControlContext(
194			new ProtectionDomain[] { new ProtectionDomain(null, null) });
195			}
196			static ThreadGroup createGroup() {
197			ThreadGroup group = Thread.currentThread().getThreadGroup();
198			for (ThreadGroup p; (p = group.getParent()) != null; )
199			group = p;
200			return new ThreadGroup(group, "InnocuousForkJoinWorkerThreadGroup");
201			}
202			static {
203			@SuppressWarnings("removal")
204			SecurityManager sm = System.getSecurityManager();
205			@SuppressWarnings("removal")
206			ThreadGroup g = innocuousThreadGroup =
207			(sm == null) ? createGroup() :
208			AccessController.doPrivileged(new PrivilegedAction<>() {
209			public ThreadGroup run() {
210			return createGroup(); }});
211			@SuppressWarnings("removal")
212			AccessControlContext a = innocuousACC =
213			(sm == null) ? createACC() :
214			AccessController.doPrivileged(new PrivilegedAction<>() {
215			public AccessControlContext run() {
216			return createACC(); }});
217			}
218	jsr166	1.1	}
219			}