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) {
        super(group, null, pool.nextWorkerThreadName(), 0L);
        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.
     *
     * @param group if non-null, the thread group for this thread
     * @param pool the pool this thread works in
     * @throws NullPointerException if pool is null
     */
    ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool) {
        this(group, pool, false);
    }

    /**
     * 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);
    }

    /**
     * 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);
        }

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

        @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:	1.83
Committed:	Fri Mar 18 16:01:42 2022 UTC (2 years, 2 months ago) by dl
Branch:	MAIN
Changes since 1.82:	+49 -16 lines
Log Message:	jdk17+ suppressWarnings, FJ updates
#	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	1.83	boolean useSystemClassLoader) {
47	dl	1.79	super(group, null, pool.nextWorkerThreadName(), 0L);
48			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			* pool.
60			*
61			* @param group if non-null, the thread group for this thread
62			* @param pool the pool this thread works in
63			* @throws NullPointerException if pool is null
64	jsr166	1.74	*/
65	dl	1.83	ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool) {
66			this(group, pool, false);
67	jsr166	1.74	}
68
69			/**
70	dl	1.79	* Creates a ForkJoinWorkerThread operating in the given pool.
71			*
72			* @param pool the pool this thread works in
73			* @throws NullPointerException if pool is null
74	dl	1.60	*/
75	dl	1.79	protected ForkJoinWorkerThread(ForkJoinPool pool) {
76	dl	1.83	this(null, pool, false);
77	dl	1.60	}
78
79			/**
80	jsr166	1.1	* Returns the pool hosting this thread.
81			*
82			* @return the pool
83			*/
84			public ForkJoinPool getPool() {
85			return pool;
86			}
87
88			/**
89	jsr166	1.59	* Returns the unique index number of this thread in its pool.
90			* The returned value ranges from zero to the maximum number of
91			* threads (minus one) that may exist in the pool, and does not
92			* change during the lifetime of the thread. This method may be
93			* useful for applications that track status or collect results
94			* per-worker-thread rather than per-task.
95	jsr166	1.1	*
96			* @return the index number
97			*/
98			public int getPoolIndex() {
99	dl	1.65	return workQueue.getPoolIndex();
100	dl	1.45	}
101
102	jsr166	1.1	/**
103	dl	1.14	* Initializes internal state after construction but before
104			* processing any tasks. If you override this method, you must
105	jsr166	1.39	* invoke {@code super.onStart()} at the beginning of the method.
106	dl	1.14	* Initialization requires care: Most fields must have legal
107			* default values, to ensure that attempted accesses from other
108			* threads work correctly even before this thread starts
109			* processing tasks.
110	jsr166	1.1	*/
111	dl	1.14	protected void onStart() {
112			}
113	jsr166	1.1
114			/**
115	dl	1.14	* Performs cleanup associated with termination of this worker
116			* thread. If you override this method, you must invoke
117			* {@code super.onTermination} at the end of the overridden method.
118	jsr166	1.4	*
119	dl	1.14	* @param exception the exception causing this thread to abort due
120			* to an unrecoverable error, or {@code null} if completed normally
121	jsr166	1.1	*/
122	dl	1.14	protected void onTermination(Throwable exception) {
123	jsr166	1.1	}
124
125			/**
126			* This method is required to be public, but should never be
127			* called explicitly. It performs the main run loop to execute
128	jsr166	1.40	* {@link ForkJoinTask}s.
129	jsr166	1.1	*/
130			public void run() {
131	dl	1.79	Throwable exception = null;
132			ForkJoinPool p = pool;
133			ForkJoinPool.WorkQueue w = workQueue;
134			if (p != null && w != null) { // skip on failed initialization
135	dl	1.52	try {
136	dl	1.79	p.registerWorker(w);
137	dl	1.60	onStart();
138	dl	1.79	p.runWorker(w);
139	dl	1.52	} catch (Throwable ex) {
140	dl	1.60	exception = ex;
141	dl	1.52	} finally {
142	dl	1.60	try {
143			onTermination(exception);
144			} catch (Throwable ex) {
145			if (exception == null)
146			exception = ex;
147			} finally {
148	dl	1.79	p.deregisterWorker(this, exception);
149	dl	1.60	}
150			}
151			}
152			}
153
154			/**
155			* A worker thread that has no permissions, is not a member of any
156	jsr166	1.74	* user-defined ThreadGroup, uses the system class loader as
157			* thread context class loader, and erases all ThreadLocals after
158	dl	1.60	* running each top-level task.
159			*/
160			static final class InnocuousForkJoinWorkerThread extends ForkJoinWorkerThread {
161			/** The ThreadGroup for all InnocuousForkJoinWorkerThreads */
162	dl	1.83	private static final ThreadGroup innocuousThreadGroup;
163			@SuppressWarnings("removal")
164			private static final AccessControlContext innocuousACC;
165			InnocuousForkJoinWorkerThread(ForkJoinPool pool) {
166			super(innocuousThreadGroup, pool, true);
167			}
168	dl	1.60
169	dl	1.83	@Override @SuppressWarnings("removal")
170			protected void onStart() {
171			ForkJoinPool.WorkQueue w = workQueue;
172			if (w != null)
173			w.setInnocuous();
174			Thread t = Thread.currentThread();
175			ThreadLocalRandom.setInheritedAccessControlContext(t, innocuousACC);
176			ThreadLocalRandom.eraseThreadLocals(t);
177	dl	1.60	}
178
179			@Override // to silently fail
180			public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { }
181
182			@Override // paranoically
183			public void setContextClassLoader(ClassLoader cl) {
184	dl	1.78	if (cl != null && ClassLoader.getSystemClassLoader() != cl)
185	dl	1.77	throw new SecurityException("setContextClassLoader");
186	dl	1.60	}
187	dl	1.83
188			@SuppressWarnings("removal")
189			static AccessControlContext createACC() {
190			return new AccessControlContext(
191			new ProtectionDomain[] { new ProtectionDomain(null, null) });
192			}
193			static ThreadGroup createGroup() {
194			ThreadGroup group = Thread.currentThread().getThreadGroup();
195			for (ThreadGroup p; (p = group.getParent()) != null; )
196			group = p;
197			return new ThreadGroup(group, "InnocuousForkJoinWorkerThreadGroup");
198			}
199			static {
200			@SuppressWarnings("removal")
201			SecurityManager sm = System.getSecurityManager();
202			@SuppressWarnings("removal")
203			ThreadGroup g = innocuousThreadGroup =
204			(sm == null) ? createGroup() :
205			AccessController.doPrivileged(new PrivilegedAction<>() {
206			public ThreadGroup run() {
207			return createGroup(); }});
208			@SuppressWarnings("removal")
209			AccessControlContext a = innocuousACC =
210			(sm == null) ? createACC() :
211			AccessController.doPrivileged(new PrivilegedAction<>() {
212			public AccessControlContext run() {
213			return createACC(); }});
214			}
215	jsr166	1.1	}
216			}