util/concurrent/Executors.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain. Use, modify, and
 * redistribute this code in any way without acknowledgement.
 */

package java.util.concurrent;
import java.util.*;
import java.util.concurrent.atomic.AtomicInteger;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.PrivilegedExceptionAction;

/**
 * Factory and utility methods for {@link Executor}, {@link
 * ExecutorService}, {@link ThreadFactory}, {@link Future}, and {@link
 * Cancellable} classes defined in this package.
 *
 * @since 1.5
 * @author Doug Lea
 */
public class Executors {

    /**
     * A wrapper class that exposes only the ExecutorService methods
     * of an implementation.
     */
    private static class DelegatedExecutorService implements ExecutorService {
        private final ExecutorService e;
        DelegatedExecutorService(ExecutorService executor) { e = executor; }
        public void execute(Runnable command) { e.execute(command); }
        public void shutdown() { e.shutdown(); }
        public List shutdownNow() { return e.shutdownNow(); }
        public boolean isShutdown() { return e.isShutdown(); }
        public boolean isTerminated() { return e.isTerminated(); }
        public boolean awaitTermination(long timeout, TimeUnit unit)
            throws InterruptedException {
            return e.awaitTermination(timeout, unit);
        }
    }

    /**
     * Creates a thread pool that reuses a fixed set of threads
     * operating off a shared unbounded queue. If any thread
     * terminates due to a failure during execution prior to shutdown,
     * a new one will take its place if needed to execute subsequent
     * tasks.
     *
     * @param nThreads the number of threads in the pool
     * @return the newly created thread pool
     */
    public static ExecutorService newFixedThreadPool(int nThreads) {
        return new DelegatedExecutorService
            (new ThreadPoolExecutor(nThreads, nThreads,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>()));
    }

    /**
     * Creates a thread pool that reuses a fixed set of threads
     * operating off a shared unbounded queue, using the provided
     * ThreadFactory to create new threads when needed.
     *
     * @param nThreads the number of threads in the pool
     * @param threadFactory the factory to use when creating new threads
     * @return the newly created thread pool
     */
    public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
        return new DelegatedExecutorService
            (new ThreadPoolExecutor(nThreads, nThreads,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>(),
                                    threadFactory));
    }

    /**
     * Creates an Executor that uses a single worker thread operating
     * off an unbounded queue. (Note however that if this single
     * thread terminates due to a failure during execution prior to
     * shutdown, a new one will take its place if needed to execute
     * subsequent tasks.)  Tasks are guaranteed to execute
     * sequentially, and no more than one task will be active at any
     * given time. This method is equivalent in effect to
     *<tt>new FixedThreadPool(1)</tt>.
     *
     * @return the newly-created single-threaded Executor
     */
    public static ExecutorService newSingleThreadExecutor() {
        return new DelegatedExecutorService
            (new ThreadPoolExecutor(1, 1,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>()));
    }

    /**
     * Creates an Executor that uses a single worker thread operating
     * off an unbounded queue, and uses the provided ThreadFactory to
     * create new threads when needed.
     * @param threadFactory the factory to use when creating new
     * threads
     *
     * @return the newly-created single-threaded Executor
     */
    public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {
        return new DelegatedExecutorService
            (new ThreadPoolExecutor(1, 1,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>(),
                                    threadFactory));
    }

    /**
     * Creates a thread pool that creates new threads as needed, but
     * will reuse previously constructed threads when they are
     * available.  These pools will typically improve the performance
     * of programs that execute many short-lived asynchronous tasks.
     * Calls to <tt>execute</tt> will reuse previously constructed
     * threads if available. If no existing thread is available, a new
     * thread will be created and added to the pool. Threads that have
     * not been used for sixty seconds are terminated and removed from
     * the cache. Thus, a pool that remains idle for long enough will
     * not consume any resources. Note that pools with similar
     * properties but different details (for example, timeout parameters)
     * may be created using {@link ThreadPoolExecutor} constructors.
     *
     * @return the newly created thread pool
     */
    public static ExecutorService newCachedThreadPool() {
        return new DelegatedExecutorService
            (new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                    60, TimeUnit.SECONDS,
                                    new SynchronousQueue<Runnable>()));
    }

    /**
     * Creates a thread pool that creates new threads as needed, but
     * will reuse previously constructed threads when they are
     * available, and uses the provided
     * ThreadFactory to create new threads when needed.
     * @param threadFactory the factory to use when creating new threads
     * @return the newly created thread pool
     */
    public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
        return new DelegatedExecutorService
            (new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                    60, TimeUnit.SECONDS,
                                    new SynchronousQueue<Runnable>(),
                                    threadFactory));
    }

    /**
     * Executes a Runnable task and returns a Cancellable representing that
     * task.
     *
     * @param executor the Executor to which the task will be submitted
     * @param task the task to submit
     * @return a Cancellable representing pending completion of the task
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution
     */
    public static Cancellable execute(Executor executor, Runnable task) {
        FutureTask<Boolean> ftask = new FutureTask<Boolean>(task, Boolean.TRUE);
        executor.execute(ftask);
        return ftask;
    }

    /**
     * Executes a Runnable task and returns a Future representing that
     * task.
     *
     * @param executor the Executor to which the task will be submitted
     * @param task the task to submit
     * @param value the value which will become the return value of
     * the task upon task completion
     * @return a Future representing pending completion of the task
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution
     */
    public static <T> Future<T> execute(Executor executor, Runnable task, T value) {
        FutureTask<T> ftask = new FutureTask<T>(task, value);
        executor.execute(ftask);
        return ftask;
    }

    /**
     * Executes a value-returning task and returns a Future
     * representing the pending results of the task.
     *
     * @param executor the Executor to which the task will be submitted
     * @param task the task to submit
     * @return a Future representing pending completion of the task
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution
     */
    public static <T> Future<T> execute(Executor executor, Callable<T> task) {
        FutureTask<T> ftask = new FutureTask<T>(task);
        executor.execute(ftask);
        return ftask;
    }

    /**
     * Executes a Runnable task and blocks until it completes normally
     * or throws an exception.
     *
     * @param executor the Executor to which the task will be submitted
     * @param task the task to submit
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution
     * @throws ExecutionException if the task encountered an exception
     * while executing
     */
    public static void invoke(Executor executor, Runnable task)
            throws ExecutionException, InterruptedException {
        FutureTask<Boolean> ftask = new FutureTask<Boolean>(task, Boolean.TRUE);
        executor.execute(ftask);
        ftask.get();
    }

    /**
     * Executes a value-returning task and blocks until it returns a
     * value or throws an exception.
     *
     * @param executor the Executor to which the task will be submitted
     * @param task the task to submit
     * @return a Future representing pending completion of the task
     * @throws RejectedExecutionException if task cannot be scheduled
     * for execution
     * @throws InterruptedException if interrupted while waiting for
     * completion
     * @throws ExecutionException if the task encountered an exception
     * while executing
     */
    public static <T> T invoke(Executor executor, Callable<T> task)
            throws ExecutionException, InterruptedException {
        FutureTask<T> ftask = new FutureTask<T>(task);
        executor.execute(ftask);
        return ftask.get();
    }


    /**
     * Executes a privileged action under the current access control 
     * context and returns a Future representing the pending result 
     * object of that action.
     *
     * @param executor the Executor to which the task will be submitted
     * @param action the action to submit
     * @return a Future representing pending completion of the action
     * @throws RejectedExecutionException if action cannot be scheduled
     * for execution
     */
    public static Future<Object> execute(Executor executor, PrivilegedAction action) {
        Callable<Object> task = new PrivilegedActionAdapter(action);
        FutureTask<Object> future = new PrivilegedFutureTask<Object>(task);
        executor.execute(future);
        return future;
    }

    /**
     * Executes a privileged exception action under the current access control 
     * context and returns a Future representing the pending result 
     * object of that action.
     *
     * @param executor the Executor to which the task will be submitted
     * @param action the action to submit
     * @return a Future representing pending completion of the action
     * @throws RejectedExecutionException if action cannot be scheduled
     * for execution
     */
    public static Future<Object> execute(Executor executor, PrivilegedExceptionAction action) {
        Callable<Object> task = new PrivilegedExceptionActionAdapter(action);
        FutureTask<Object> future = new PrivilegedFutureTask<Object>(task);
        executor.execute(future);
        return future;
    }

    private static class PrivilegedActionAdapter implements Callable<Object> {
        PrivilegedActionAdapter(PrivilegedAction action) {
            this.action = action;
        }
        public Object call () {
            return action.run();
        }
        private final PrivilegedAction action;
    }
    
    private static class PrivilegedExceptionActionAdapter implements Callable<Object> {
        PrivilegedExceptionActionAdapter(PrivilegedExceptionAction action) {
            this.action = action;
        }
        public Object call () throws Exception {
            return action.run();
        }
        private final PrivilegedExceptionAction action;
    }
        
    /**
     * Return a default thread factory used to create new threads.
     * This factory creates all new threads used by an Executor in the
     * same {@link ThreadGroup}. If there is a {@link
     * java.lang.SecurityManager}, it uses the group of {@link
     * System#getSecurityManager}, else the group of the thread
     * invoking this <tt>defaultThreadFactory</tt> method. Each new
     * thread is created as a non-daemon thread with priority
     * <tt>Thread.NORM_PRIORITY</tt>. New threads have names
     * accessible via {@link Thread#getName} of
     * <em>pool-N-thread-M</em>, where <em>N</em> is the sequence
     * number of this factory, and <em>M</em> is the sequence number
     * of the thread created by this factory.
     * @return the thread factory
     */
    public static ThreadFactory defaultThreadFactory() {
        return new DefaultThreadFactory();
    }

    /**
     * Return a default thread factory used to create new threads.
     * This factory creates threads with the same settings as {@link
     * Executors#defaultThreadFactory}, additionally setting the
     * AccessControlContext and contextClassLoader of new threads to
     * be the same as the thread invoking this
     * <tt>privilegedThreadFactory</tt> method.  A new
     * <tt>privilegedThreadFactory</tt> can be created within an
     * {@link AccessController#doPrivileged} action setting the
     * current threads access control context to create threads with
     * the selected permission settings holding within that action.
     *
     * <p> Note that while tasks running within such threads will have
     * the same access control and class loader settings as the
     * current thread, they need not have the same {@link
     * java.lang.ThreadLocal} or {@link
     * java.lang.InheritableThreadLocal} values. If necessary,
     * particular values of thread locals can be set or reset before
     * any task runs in {@link ThreadPoolExecutor} subclasses using
     * {@link ThreadPoolExecutor#beforeExecute}. Also, if it is
     * necessary to initialize worker threads to have the same
     * InheritableThreadLocal settings as some other designated
     * thread, you can create a custom ThreadFactory in which that
     * thread waits for and services requests to create others that
     * will inherit its values.
     *
     * @return the thread factory
     * @throws AccessControlException if the current access control
     * context does not have permission to both get and set context
     * class loader.
     * @see PrivilegedFutureTask
     */
    public static ThreadFactory privilegedThreadFactory() {
        return new PrivilegedThreadFactory();
    }

    static class DefaultThreadFactory implements ThreadFactory {
        static final AtomicInteger poolNumber = new AtomicInteger(1);
        final ThreadGroup group;
        final AtomicInteger threadNumber = new AtomicInteger(1);
        final String namePrefix;

        DefaultThreadFactory() {
            SecurityManager s = System.getSecurityManager();
            group = (s != null)? s.getThreadGroup() :
                                 Thread.currentThread().getThreadGroup();
            namePrefix = "pool-" + 
                          poolNumber.getAndIncrement() + 
                         "-thread-";
        }

        public Thread newThread(Runnable r) {
            Thread t = new Thread(group, r, 
                                  namePrefix + threadNumber.getAndIncrement(),
                                  0);
            if (t.isDaemon())
                t.setDaemon(false);
            if (t.getPriority() != Thread.NORM_PRIORITY)
                t.setPriority(Thread.NORM_PRIORITY);
            return t;
        }
    }

    static class PrivilegedThreadFactory extends DefaultThreadFactory {
        private final ClassLoader ccl;
        private final AccessControlContext acc;

        PrivilegedThreadFactory() {
            super();
            this.ccl = Thread.currentThread().getContextClassLoader();
            this.acc = AccessController.getContext();
            acc.checkPermission(new RuntimePermission("setContextClassLoader"));
        }
        
        public Thread newThread(final Runnable r) {
            return super.newThread(new Runnable() {
                public void run() {
                    AccessController.doPrivileged(new PrivilegedAction() {
                        public Object run() { 
                            Thread.currentThread().setContextClassLoader(ccl);
                            r.run();
                            return null; 
                        }
                    }, acc);
                }
            });
        }
        
    }

        
    /** Cannot instantiate. */
    private Executors() {}
}
Revision:	1.23
Committed:	Fri Nov 7 12:19:35 2003 UTC (20 years, 6 months ago) by dl
Branch:	MAIN
Changes since 1.22:	+3 -6 lines
Log Message:	Clarified PFT documentation
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain. Use, modify, and
4	* redistribute this code in any way without acknowledgement.
5	*/
6
7	package java.util.concurrent;
8	import java.util.*;
9	import java.util.concurrent.atomic.AtomicInteger;
10	import java.security.AccessControlContext;
11	import java.security.AccessController;
12	import java.security.PrivilegedAction;
13	import java.security.PrivilegedExceptionAction;
14
15	/**
16	* Factory and utility methods for {@link Executor}, {@link
17	* ExecutorService}, {@link ThreadFactory}, {@link Future}, and {@link
18	* Cancellable} classes defined in this package.
19	*
20	* @since 1.5
21	* @author Doug Lea
22	*/
23	public class Executors {
24
25	/**
26	* A wrapper class that exposes only the ExecutorService methods
27	* of an implementation.
28	*/
29	private static class DelegatedExecutorService implements ExecutorService {
30	private final ExecutorService e;
31	DelegatedExecutorService(ExecutorService executor) { e = executor; }
32	public void execute(Runnable command) { e.execute(command); }
33	public void shutdown() { e.shutdown(); }
34	public List shutdownNow() { return e.shutdownNow(); }
35	public boolean isShutdown() { return e.isShutdown(); }
36	public boolean isTerminated() { return e.isTerminated(); }
37	public boolean awaitTermination(long timeout, TimeUnit unit)
38	throws InterruptedException {
39	return e.awaitTermination(timeout, unit);
40	}
41	}
42
43	/**
44	* Creates a thread pool that reuses a fixed set of threads
45	* operating off a shared unbounded queue. If any thread
46	* terminates due to a failure during execution prior to shutdown,
47	* a new one will take its place if needed to execute subsequent
48	* tasks.
49	*
50	* @param nThreads the number of threads in the pool
51	* @return the newly created thread pool
52	*/
53	public static ExecutorService newFixedThreadPool(int nThreads) {
54	return new DelegatedExecutorService
55	(new ThreadPoolExecutor(nThreads, nThreads,
56	0L, TimeUnit.MILLISECONDS,
57	new LinkedBlockingQueue<Runnable>()));
58	}
59
60	/**
61	* Creates a thread pool that reuses a fixed set of threads
62	* operating off a shared unbounded queue, using the provided
63	* ThreadFactory to create new threads when needed.
64	*
65	* @param nThreads the number of threads in the pool
66	* @param threadFactory the factory to use when creating new threads
67	* @return the newly created thread pool
68	*/
69	public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
70	return new DelegatedExecutorService
71	(new ThreadPoolExecutor(nThreads, nThreads,
72	0L, TimeUnit.MILLISECONDS,
73	new LinkedBlockingQueue<Runnable>(),
74	threadFactory));
75	}
76
77	/**
78	* Creates an Executor that uses a single worker thread operating
79	* off an unbounded queue. (Note however that if this single
80	* thread terminates due to a failure during execution prior to
81	* shutdown, a new one will take its place if needed to execute
82	* subsequent tasks.) Tasks are guaranteed to execute
83	* sequentially, and no more than one task will be active at any
84	* given time. This method is equivalent in effect to
85	*<tt>new FixedThreadPool(1)</tt>.
86	*
87	* @return the newly-created single-threaded Executor
88	*/
89	public static ExecutorService newSingleThreadExecutor() {
90	return new DelegatedExecutorService
91	(new ThreadPoolExecutor(1, 1,
92	0L, TimeUnit.MILLISECONDS,
93	new LinkedBlockingQueue<Runnable>()));
94	}
95
96	/**
97	* Creates an Executor that uses a single worker thread operating
98	* off an unbounded queue, and uses the provided ThreadFactory to
99	* create new threads when needed.
100	* @param threadFactory the factory to use when creating new
101	* threads
102	*
103	* @return the newly-created single-threaded Executor
104	*/
105	public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {
106	return new DelegatedExecutorService
107	(new ThreadPoolExecutor(1, 1,
108	0L, TimeUnit.MILLISECONDS,
109	new LinkedBlockingQueue<Runnable>(),
110	threadFactory));
111	}
112
113	/**
114	* Creates a thread pool that creates new threads as needed, but
115	* will reuse previously constructed threads when they are
116	* available. These pools will typically improve the performance
117	* of programs that execute many short-lived asynchronous tasks.
118	* Calls to <tt>execute</tt> will reuse previously constructed
119	* threads if available. If no existing thread is available, a new
120	* thread will be created and added to the pool. Threads that have
121	* not been used for sixty seconds are terminated and removed from
122	* the cache. Thus, a pool that remains idle for long enough will
123	* not consume any resources. Note that pools with similar
124	* properties but different details (for example, timeout parameters)
125	* may be created using {@link ThreadPoolExecutor} constructors.
126	*
127	* @return the newly created thread pool
128	*/
129	public static ExecutorService newCachedThreadPool() {
130	return new DelegatedExecutorService
131	(new ThreadPoolExecutor(0, Integer.MAX_VALUE,
132	60, TimeUnit.SECONDS,
133	new SynchronousQueue<Runnable>()));
134	}
135
136	/**
137	* Creates a thread pool that creates new threads as needed, but
138	* will reuse previously constructed threads when they are
139	* available, and uses the provided
140	* ThreadFactory to create new threads when needed.
141	* @param threadFactory the factory to use when creating new threads
142	* @return the newly created thread pool
143	*/
144	public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
145	return new DelegatedExecutorService
146	(new ThreadPoolExecutor(0, Integer.MAX_VALUE,
147	60, TimeUnit.SECONDS,
148	new SynchronousQueue<Runnable>(),
149	threadFactory));
150	}
151
152	/**
153	* Executes a Runnable task and returns a Cancellable representing that
154	* task.
155	*
156	* @param executor the Executor to which the task will be submitted
157	* @param task the task to submit
158	* @return a Cancellable representing pending completion of the task
159	* @throws RejectedExecutionException if task cannot be scheduled
160	* for execution
161	*/
162	public static Cancellable execute(Executor executor, Runnable task) {
163	FutureTask<Boolean> ftask = new FutureTask<Boolean>(task, Boolean.TRUE);
164	executor.execute(ftask);
165	return ftask;
166	}
167
168	/**
169	* Executes a Runnable task and returns a Future representing that
170	* task.
171	*
172	* @param executor the Executor to which the task will be submitted
173	* @param task the task to submit
174	* @param value the value which will become the return value of
175	* the task upon task completion
176	* @return a Future representing pending completion of the task
177	* @throws RejectedExecutionException if task cannot be scheduled
178	* for execution
179	*/
180	public static <T> Future<T> execute(Executor executor, Runnable task, T value) {
181	FutureTask<T> ftask = new FutureTask<T>(task, value);
182	executor.execute(ftask);
183	return ftask;
184	}
185
186	/**
187	* Executes a value-returning task and returns a Future
188	* representing the pending results of the task.
189	*
190	* @param executor the Executor to which the task will be submitted
191	* @param task the task to submit
192	* @return a Future representing pending completion of the task
193	* @throws RejectedExecutionException if task cannot be scheduled
194	* for execution
195	*/
196	public static <T> Future<T> execute(Executor executor, Callable<T> task) {
197	FutureTask<T> ftask = new FutureTask<T>(task);
198	executor.execute(ftask);
199	return ftask;
200	}
201
202	/**
203	* Executes a Runnable task and blocks until it completes normally
204	* or throws an exception.
205	*
206	* @param executor the Executor to which the task will be submitted
207	* @param task the task to submit
208	* @throws RejectedExecutionException if task cannot be scheduled
209	* for execution
210	* @throws ExecutionException if the task encountered an exception
211	* while executing
212	*/
213	public static void invoke(Executor executor, Runnable task)
214	throws ExecutionException, InterruptedException {
215	FutureTask<Boolean> ftask = new FutureTask<Boolean>(task, Boolean.TRUE);
216	executor.execute(ftask);
217	ftask.get();
218	}
219
220	/**
221	* Executes a value-returning task and blocks until it returns a
222	* value or throws an exception.
223	*
224	* @param executor the Executor to which the task will be submitted
225	* @param task the task to submit
226	* @return a Future representing pending completion of the task
227	* @throws RejectedExecutionException if task cannot be scheduled
228	* for execution
229	* @throws InterruptedException if interrupted while waiting for
230	* completion
231	* @throws ExecutionException if the task encountered an exception
232	* while executing
233	*/
234	public static <T> T invoke(Executor executor, Callable<T> task)
235	throws ExecutionException, InterruptedException {
236	FutureTask<T> ftask = new FutureTask<T>(task);
237	executor.execute(ftask);
238	return ftask.get();
239	}
240
241
242	/**
243	* Executes a privileged action under the current access control
244	* context and returns a Future representing the pending result
245	* object of that action.
246	*
247	* @param executor the Executor to which the task will be submitted
248	* @param action the action to submit
249	* @return a Future representing pending completion of the action
250	* @throws RejectedExecutionException if action cannot be scheduled
251	* for execution
252	*/
253	public static Future<Object> execute(Executor executor, PrivilegedAction action) {
254	Callable<Object> task = new PrivilegedActionAdapter(action);
255	FutureTask<Object> future = new PrivilegedFutureTask<Object>(task);
256	executor.execute(future);
257	return future;
258	}
259
260	/**
261	* Executes a privileged exception action under the current access control
262	* context and returns a Future representing the pending result
263	* object of that action.
264	*
265	* @param executor the Executor to which the task will be submitted
266	* @param action the action to submit
267	* @return a Future representing pending completion of the action
268	* @throws RejectedExecutionException if action cannot be scheduled
269	* for execution
270	*/
271	public static Future<Object> execute(Executor executor, PrivilegedExceptionAction action) {
272	Callable<Object> task = new PrivilegedExceptionActionAdapter(action);
273	FutureTask<Object> future = new PrivilegedFutureTask<Object>(task);
274	executor.execute(future);
275	return future;
276	}
277
278	private static class PrivilegedActionAdapter implements Callable<Object> {
279	PrivilegedActionAdapter(PrivilegedAction action) {
280	this.action = action;
281	}
282	public Object call () {
283	return action.run();
284	}
285	private final PrivilegedAction action;
286	}
287
288	private static class PrivilegedExceptionActionAdapter implements Callable<Object> {
289	PrivilegedExceptionActionAdapter(PrivilegedExceptionAction action) {
290	this.action = action;
291	}
292	public Object call () throws Exception {
293	return action.run();
294	}
295	private final PrivilegedExceptionAction action;
296	}
297
298	/**
299	* Return a default thread factory used to create new threads.
300	* This factory creates all new threads used by an Executor in the
301	* same {@link ThreadGroup}. If there is a {@link
302	* java.lang.SecurityManager}, it uses the group of {@link
303	* System#getSecurityManager}, else the group of the thread
304	* invoking this <tt>defaultThreadFactory</tt> method. Each new
305	* thread is created as a non-daemon thread with priority
306	* <tt>Thread.NORM_PRIORITY</tt>. New threads have names
307	* accessible via {@link Thread#getName} of
308	* <em>pool-N-thread-M</em>, where <em>N</em> is the sequence
309	* number of this factory, and <em>M</em> is the sequence number
310	* of the thread created by this factory.
311	* @return the thread factory
312	*/
313	public static ThreadFactory defaultThreadFactory() {
314	return new DefaultThreadFactory();
315	}
316
317	/**
318	* Return a default thread factory used to create new threads.
319	* This factory creates threads with the same settings as {@link
320	* Executors#defaultThreadFactory}, additionally setting the
321	* AccessControlContext and contextClassLoader of new threads to
322	* be the same as the thread invoking this
323	* <tt>privilegedThreadFactory</tt> method. A new
324	* <tt>privilegedThreadFactory</tt> can be created within an
325	* {@link AccessController#doPrivileged} action setting the
326	* current threads access control context to create threads with
327	* the selected permission settings holding within that action.
328	*
329	* <p> Note that while tasks running within such threads will have
330	* the same access control and class loader settings as the
331	* current thread, they need not have the same {@link
332	* java.lang.ThreadLocal} or {@link
333	* java.lang.InheritableThreadLocal} values. If necessary,
334	* particular values of thread locals can be set or reset before
335	* any task runs in {@link ThreadPoolExecutor} subclasses using
336	* {@link ThreadPoolExecutor#beforeExecute}. Also, if it is
337	* necessary to initialize worker threads to have the same
338	* InheritableThreadLocal settings as some other designated
339	* thread, you can create a custom ThreadFactory in which that
340	* thread waits for and services requests to create others that
341	* will inherit its values.
342	*
343	* @return the thread factory
344	* @throws AccessControlException if the current access control
345	* context does not have permission to both get and set context
346	* class loader.
347	* @see PrivilegedFutureTask
348	*/
349	public static ThreadFactory privilegedThreadFactory() {
350	return new PrivilegedThreadFactory();
351	}
352
353	static class DefaultThreadFactory implements ThreadFactory {
354	static final AtomicInteger poolNumber = new AtomicInteger(1);
355	final ThreadGroup group;
356	final AtomicInteger threadNumber = new AtomicInteger(1);
357	final String namePrefix;
358
359	DefaultThreadFactory() {
360	SecurityManager s = System.getSecurityManager();
361	group = (s != null)? s.getThreadGroup() :
362	Thread.currentThread().getThreadGroup();
363	namePrefix = "pool-" +
364	poolNumber.getAndIncrement() +
365	"-thread-";
366	}
367
368	public Thread newThread(Runnable r) {
369	Thread t = new Thread(group, r,
370	namePrefix + threadNumber.getAndIncrement(),
371	0);
372	if (t.isDaemon())
373	t.setDaemon(false);
374	if (t.getPriority() != Thread.NORM_PRIORITY)
375	t.setPriority(Thread.NORM_PRIORITY);
376	return t;
377	}
378	}
379
380	static class PrivilegedThreadFactory extends DefaultThreadFactory {
381	private final ClassLoader ccl;
382	private final AccessControlContext acc;
383
384	PrivilegedThreadFactory() {
385	super();
386	this.ccl = Thread.currentThread().getContextClassLoader();
387	this.acc = AccessController.getContext();
388	acc.checkPermission(new RuntimePermission("setContextClassLoader"));
389	}
390
391	public Thread newThread(final Runnable r) {
392	return super.newThread(new Runnable() {
393	public void run() {
394	AccessController.doPrivileged(new PrivilegedAction() {
395	public Object run() {
396	Thread.currentThread().setContextClassLoader(ccl);
397	r.run();
398	return null;
399	}
400	}, acc);
401	}
402	});
403	}
404
405	}
406
407
408	/** Cannot instantiate. */
409	private Executors() {}
410	}