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.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 Unsafe)
     * 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 InnocuousForkJoinWorkerThread.
     */
    ForkJoinWorkerThread(ForkJoinPool pool, ThreadGroup threadGroup,
                         AccessControlContext acc) {
        super(threadGroup, null, "aForkJoinWorkerThread");
        U.putOrderedObject(this, INHERITEDACCESSCONTROLCONTEXT, acc);
        eraseThreadLocals(); // 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);
                }
            }
        }
    }

    /**
     * Erases ThreadLocals by nulling out Thread maps.
     */
    final void eraseThreadLocals() {
        U.putObject(this, THREADLOCALS, null);
        U.putObject(this, INHERITABLETHREADLOCALS, null);
    }

    /**
     * Non-public hook method for InnocuousForkJoinWorkerThread.
     */
    void afterTopLevelExec() {
    }

    // Set up to allow setting thread fields in constructor
    private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe();
    private static final long THREADLOCALS;
    private static final long INHERITABLETHREADLOCALS;
    private static final long INHERITEDACCESSCONTROLCONTEXT;
    static {
        try {
            THREADLOCALS = U.objectFieldOffset
                (Thread.class.getDeclaredField("threadLocals"));
            INHERITABLETHREADLOCALS = U.objectFieldOffset
                (Thread.class.getDeclaredField("inheritableThreadLocals"));
            INHERITEDACCESSCONTROLCONTEXT = U.objectFieldOffset
                (Thread.class.getDeclaredField("inheritedAccessControlContext"));
        } catch (ReflectiveOperationException e) {
            throw new Error(e);
        }
    }

    /**
     * A worker thread that has no permissions, is not a member of any
     * user-defined ThreadGroup, 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 =
            createThreadGroup();

        /** An AccessControlContext supporting no privileges */
        private static final AccessControlContext INNOCUOUS_ACC =
            new AccessControlContext(
                new ProtectionDomain[] {
                    new ProtectionDomain(null, null)
                });

        InnocuousForkJoinWorkerThread(ForkJoinPool pool) {
            super(pool, innocuousThreadGroup, INNOCUOUS_ACC);
        }

        @Override // to erase ThreadLocals
        void afterTopLevelExec() {
            eraseThreadLocals();
        }

        @Override // to always report system loader
        public ClassLoader getContextClassLoader() {
            return ClassLoader.getSystemClassLoader();
        }

        @Override // to silently fail
        public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { }

        @Override // paranoically
        public void setContextClassLoader(ClassLoader cl) {
            throw new SecurityException("setContextClassLoader");
        }

        /**
         * Returns a new group with the system ThreadGroup (the
         * topmost, parent-less group) as parent.  Uses Unsafe to
         * traverse Thread.group and ThreadGroup.parent fields.
         */
        private static ThreadGroup createThreadGroup() {
            try {
                sun.misc.Unsafe u = sun.misc.Unsafe.getUnsafe();
                long tg = u.objectFieldOffset
                    (Thread.class.getDeclaredField("group"));
                long gp = u.objectFieldOffset
                    (ThreadGroup.class.getDeclaredField("parent"));
                ThreadGroup group = (ThreadGroup)
                    u.getObject(Thread.currentThread(), tg);
                while (group != null) {
                    ThreadGroup parent = (ThreadGroup)u.getObject(group, gp);
                    if (parent == null)
                        return new ThreadGroup(group,
                                               "InnocuousForkJoinWorkerThreadGroup");
                    group = parent;
                }
            } catch (ReflectiveOperationException e) {
                throw new Error(e);
            }
            // fall through if null as cannot-happen safeguard
            throw new Error("Cannot create ThreadGroup");
        }
    }

}
Revision:	1.1
Committed:	Sat Mar 26 06:22:50 2016 UTC (8 years, 2 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Log Message:	fork jdk8 maintenance branch for source and jtreg tests
#	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.ProtectionDomain;
11
12	/**
13	* A thread managed by a {@link ForkJoinPool}, which executes
14	* {@link ForkJoinTask}s.
15	* This class is subclassable solely for the sake of adding
16	* functionality -- there are no overridable methods dealing with
17	* scheduling or execution. However, you can override initialization
18	* and termination methods surrounding the main task processing loop.
19	* If you do create such a subclass, you will also need to supply a
20	* custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to
21	* {@linkplain ForkJoinPool#ForkJoinPool use it} in a {@code ForkJoinPool}.
22	*
23	* @since 1.7
24	* @author Doug Lea
25	*/
26	public class ForkJoinWorkerThread extends Thread {
27	/*
28	* ForkJoinWorkerThreads are managed by ForkJoinPools and perform
29	* ForkJoinTasks. For explanation, see the internal documentation
30	* of class ForkJoinPool.
31	*
32	* This class just maintains links to its pool and WorkQueue. The
33	* pool field is set immediately upon construction, but the
34	* workQueue field is not set until a call to registerWorker
35	* completes. This leads to a visibility race, that is tolerated
36	* by requiring that the workQueue field is only accessed by the
37	* owning thread.
38	*
39	* Support for (non-public) subclass InnocuousForkJoinWorkerThread
40	* requires that we break quite a lot of encapsulation (via Unsafe)
41	* both here and in the subclass to access and set Thread fields.
42	*/
43
44	final ForkJoinPool pool; // the pool this thread works in
45	final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics
46
47	/**
48	* Creates a ForkJoinWorkerThread operating in the given pool.
49	*
50	* @param pool the pool this thread works in
51	* @throws NullPointerException if pool is null
52	*/
53	protected ForkJoinWorkerThread(ForkJoinPool pool) {
54	// Use a placeholder until a useful name can be set in registerWorker
55	super("aForkJoinWorkerThread");
56	this.pool = pool;
57	this.workQueue = pool.registerWorker(this);
58	}
59
60	/**
61	* Version for InnocuousForkJoinWorkerThread.
62	*/
63	ForkJoinWorkerThread(ForkJoinPool pool, ThreadGroup threadGroup,
64	AccessControlContext acc) {
65	super(threadGroup, null, "aForkJoinWorkerThread");
66	U.putOrderedObject(this, INHERITEDACCESSCONTROLCONTEXT, acc);
67	eraseThreadLocals(); // clear before registering
68	this.pool = pool;
69	this.workQueue = pool.registerWorker(this);
70	}
71
72	/**
73	* Returns the pool hosting this thread.
74	*
75	* @return the pool
76	*/
77	public ForkJoinPool getPool() {
78	return pool;
79	}
80
81	/**
82	* Returns the unique index number of this thread in its pool.
83	* The returned value ranges from zero to the maximum number of
84	* threads (minus one) that may exist in the pool, and does not
85	* change during the lifetime of the thread. This method may be
86	* useful for applications that track status or collect results
87	* per-worker-thread rather than per-task.
88	*
89	* @return the index number
90	*/
91	public int getPoolIndex() {
92	return workQueue.getPoolIndex();
93	}
94
95	/**
96	* Initializes internal state after construction but before
97	* processing any tasks. If you override this method, you must
98	* invoke {@code super.onStart()} at the beginning of the method.
99	* Initialization requires care: Most fields must have legal
100	* default values, to ensure that attempted accesses from other
101	* threads work correctly even before this thread starts
102	* processing tasks.
103	*/
104	protected void onStart() {
105	}
106
107	/**
108	* Performs cleanup associated with termination of this worker
109	* thread. If you override this method, you must invoke
110	* {@code super.onTermination} at the end of the overridden method.
111	*
112	* @param exception the exception causing this thread to abort due
113	* to an unrecoverable error, or {@code null} if completed normally
114	*/
115	protected void onTermination(Throwable exception) {
116	}
117
118	/**
119	* This method is required to be public, but should never be
120	* called explicitly. It performs the main run loop to execute
121	* {@link ForkJoinTask}s.
122	*/
123	public void run() {
124	if (workQueue.array == null) { // only run once
125	Throwable exception = null;
126	try {
127	onStart();
128	pool.runWorker(workQueue);
129	} catch (Throwable ex) {
130	exception = ex;
131	} finally {
132	try {
133	onTermination(exception);
134	} catch (Throwable ex) {
135	if (exception == null)
136	exception = ex;
137	} finally {
138	pool.deregisterWorker(this, exception);
139	}
140	}
141	}
142	}
143
144	/**
145	* Erases ThreadLocals by nulling out Thread maps.
146	*/
147	final void eraseThreadLocals() {
148	U.putObject(this, THREADLOCALS, null);
149	U.putObject(this, INHERITABLETHREADLOCALS, null);
150	}
151
152	/**
153	* Non-public hook method for InnocuousForkJoinWorkerThread.
154	*/
155	void afterTopLevelExec() {
156	}
157
158	// Set up to allow setting thread fields in constructor
159	private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe();
160	private static final long THREADLOCALS;
161	private static final long INHERITABLETHREADLOCALS;
162	private static final long INHERITEDACCESSCONTROLCONTEXT;
163	static {
164	try {
165	THREADLOCALS = U.objectFieldOffset
166	(Thread.class.getDeclaredField("threadLocals"));
167	INHERITABLETHREADLOCALS = U.objectFieldOffset
168	(Thread.class.getDeclaredField("inheritableThreadLocals"));
169	INHERITEDACCESSCONTROLCONTEXT = U.objectFieldOffset
170	(Thread.class.getDeclaredField("inheritedAccessControlContext"));
171	} catch (ReflectiveOperationException e) {
172	throw new Error(e);
173	}
174	}
175
176	/**
177	* A worker thread that has no permissions, is not a member of any
178	* user-defined ThreadGroup, and erases all ThreadLocals after
179	* running each top-level task.
180	*/
181	static final class InnocuousForkJoinWorkerThread extends ForkJoinWorkerThread {
182	/** The ThreadGroup for all InnocuousForkJoinWorkerThreads */
183	private static final ThreadGroup innocuousThreadGroup =
184	createThreadGroup();
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, innocuousThreadGroup, INNOCUOUS_ACC);
195	}
196
197	@Override // to erase ThreadLocals
198	void afterTopLevelExec() {
199	eraseThreadLocals();
200	}
201
202	@Override // to always report system loader
203	public ClassLoader getContextClassLoader() {
204	return ClassLoader.getSystemClassLoader();
205	}
206
207	@Override // to silently fail
208	public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { }
209
210	@Override // paranoically
211	public void setContextClassLoader(ClassLoader cl) {
212	throw new SecurityException("setContextClassLoader");
213	}
214
215	/**
216	* Returns a new group with the system ThreadGroup (the
217	* topmost, parent-less group) as parent. Uses Unsafe to
218	* traverse Thread.group and ThreadGroup.parent fields.
219	*/
220	private static ThreadGroup createThreadGroup() {
221	try {
222	sun.misc.Unsafe u = sun.misc.Unsafe.getUnsafe();
223	long tg = u.objectFieldOffset
224	(Thread.class.getDeclaredField("group"));
225	long gp = u.objectFieldOffset
226	(ThreadGroup.class.getDeclaredField("parent"));
227	ThreadGroup group = (ThreadGroup)
228	u.getObject(Thread.currentThread(), tg);
229	while (group != null) {
230	ThreadGroup parent = (ThreadGroup)u.getObject(group, gp);
231	if (parent == null)
232	return new ThreadGroup(group,
233	"InnocuousForkJoinWorkerThreadGroup");
234	group = parent;
235	}
236	} catch (ReflectiveOperationException e) {
237	throw new Error(e);
238	}
239	// fall through if null as cannot-happen safeguard
240	throw new Error("Cannot create ThreadGroup");
241	}
242	}
243
244	}