1 /*
2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation. Oracle designates this
7 * particular file as subject to the "Classpath" exception as provided
8 * by Oracle in the LICENSE file that accompanied this code.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 */
24
25 /*
26 * This file is available under and governed by the GNU General Public
27 * License version 2 only, as published by the Free Software Foundation.
28 * However, the following notice accompanied the original version of this
29 * file:
30 *
31 * Written by Doug Lea with assistance from members of JCP JSR-166
32 * Expert Group and released to the public domain, as explained at
33 * http://creativecommons.org/publicdomain/zero/1.0/
34 */
35
36 package java.util.concurrent;
37
38 import java.security.AccessController;
39 import java.security.PrivilegedAction;
40
41 /**
42 * A thread managed by a {@link ForkJoinPool}, which executes
43 * {@link ForkJoinTask}s.
44 * This class is subclassable solely for the sake of adding
45 * functionality -- there are no overridable methods dealing with
46 * scheduling or execution. However, you can override initialization
47 * and termination methods surrounding the main task processing loop.
48 * If you do create such a subclass, you will also need to supply a
49 * custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to
50 * {@linkplain ForkJoinPool#ForkJoinPool(int, ForkJoinWorkerThreadFactory,
51 * UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)
52 * use it} in a {@code ForkJoinPool}.
53 *
54 * @since 1.7
55 * @author Doug Lea
56 */
57 public class ForkJoinWorkerThread extends Thread {
58 /*
59 * ForkJoinWorkerThreads are managed by ForkJoinPools and perform
60 * ForkJoinTasks. For explanation, see the internal documentation
61 * of class ForkJoinPool.
62 *
63 * This class just maintains links to its pool and WorkQueue.
64 */
65
66 final ForkJoinPool pool; // the pool this thread works in
67 final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics
68
69 /**
70 * Full nonpublic constructor.
71 */
72 ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool,
73 boolean useSystemClassLoader, boolean isInnocuous) {
74 super(group, null, pool.nextWorkerThreadName(), 0L);
75 UncaughtExceptionHandler handler = (this.pool = pool).ueh;
76 this.workQueue = new ForkJoinPool.WorkQueue(this, isInnocuous);
77 super.setDaemon(true);
78 if (handler != null)
79 super.setUncaughtExceptionHandler(handler);
80 if (useSystemClassLoader)
81 super.setContextClassLoader(ClassLoader.getSystemClassLoader());
82 }
83
84 /**
85 * Creates a ForkJoinWorkerThread operating in the given thread group and
86 * pool.
87 *
88 * @param group if non-null, the thread group for this thread
89 * @param pool the pool this thread works in
90 * @throws NullPointerException if pool is null
91 */
92 /* TODO: protected */ ForkJoinWorkerThread(ThreadGroup group, ForkJoinPool pool) {
93 this(group, pool, false, false);
94 }
95
96 /**
97 * Creates a ForkJoinWorkerThread operating in the given pool.
98 *
99 * @param pool the pool this thread works in
100 * @throws NullPointerException if pool is null
101 */
102 protected ForkJoinWorkerThread(ForkJoinPool pool) {
103 this(null, pool, false, false);
104 }
105
106 /**
107 * Returns the pool hosting this thread.
108 *
109 * @return the pool
110 */
111 public ForkJoinPool getPool() {
112 return pool;
113 }
114
115 /**
116 * Returns the unique index number of this thread in its pool.
117 * The returned value ranges from zero to the maximum number of
118 * threads (minus one) that may exist in the pool, and does not
119 * change during the lifetime of the thread. This method may be
120 * useful for applications that track status or collect results
121 * per-worker-thread rather than per-task.
122 *
123 * @return the index number
124 */
125 public int getPoolIndex() {
126 return workQueue.getPoolIndex();
127 }
128
129 /**
130 * Initializes internal state after construction but before
131 * processing any tasks. If you override this method, you must
132 * invoke {@code super.onStart()} at the beginning of the method.
133 * Initialization requires care: Most fields must have legal
134 * default values, to ensure that attempted accesses from other
135 * threads work correctly even before this thread starts
136 * processing tasks.
137 */
138 protected void onStart() {
139 }
140
141 /**
142 * Performs cleanup associated with termination of this worker
143 * thread. If you override this method, you must invoke
144 * {@code super.onTermination} at the end of the overridden method.
145 *
146 * @param exception the exception causing this thread to abort due
147 * to an unrecoverable error, or {@code null} if completed normally
148 */
149 protected void onTermination(Throwable exception) {
150 }
151
152 /**
153 * This method is required to be public, but should never be
154 * called explicitly. It performs the main run loop to execute
155 * {@link ForkJoinTask}s.
156 */
157 public void run() {
158 Throwable exception = null;
159 ForkJoinPool p = pool;
160 ForkJoinPool.WorkQueue w = workQueue;
161 if (p != null && w != null) { // skip on failed initialization
162 try {
163 p.registerWorker(w);
164 onStart();
165 p.runWorker(w);
166 } catch (Throwable ex) {
167 exception = ex;
168 } finally {
169 try {
170 onTermination(exception);
171 } catch (Throwable ex) {
172 if (exception == null)
173 exception = ex;
174 } finally {
175 p.deregisterWorker(this, exception);
176 }
177 }
178 }
179 }
180
181 /**
182 * A worker thread that has no permissions, is not a member of any
183 * user-defined ThreadGroup, uses the system class loader as
184 * thread context class loader, and erases all ThreadLocals after
185 * running each top-level task.
186 */
187 static final class InnocuousForkJoinWorkerThread extends ForkJoinWorkerThread {
188 /** The ThreadGroup for all InnocuousForkJoinWorkerThreads */
189 private static final ThreadGroup innocuousThreadGroup =
190 AccessController.doPrivileged(new PrivilegedAction<>() {
191 public ThreadGroup run() {
192 ThreadGroup group = Thread.currentThread().getThreadGroup();
193 for (ThreadGroup p; (p = group.getParent()) != null; )
194 group = p;
195 return new ThreadGroup(
196 group, "InnocuousForkJoinWorkerThreadGroup");
197 }});
198
199 InnocuousForkJoinWorkerThread(ForkJoinPool pool) {
200 super(innocuousThreadGroup, pool, true, true);
201 }
202
203 @Override // to silently fail
204 public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { }
205
206 @Override // paranoically
207 public void setContextClassLoader(ClassLoader cl) {
208 if (cl != null && ClassLoader.getSystemClassLoader() != cl)
209 throw new SecurityException("setContextClassLoader");
210 }
211 }
212 }