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.*;

/**
 * Factory and utility methods for the <tt>Executor</tt> classes
 * defined in <tt>java.util.concurrent</tt>.
 *
 * <p>An Executor is a framework for executing Runnables.  The
 * Executor manages queueing and scheduling of tasks, and creation and
 * teardown of threads.  Depending on which concrete Executor class is
 * being used, tasks may execute in a newly created thread, an
 * existing task-execution thread, or the thread calling execute(),
 * and may execute sequentially or concurrently.
 *
 * @since 1.5
 * @see Executor
 * @see ExecutorService
 * @see Future
 *
 * @spec JSR-166
 * @revised $Date: 2003/02/28 03:53:49 $
 * @editor $Author: brian $
 */
public class Executors {

    /**
     * A wrapper class that exposes only the ExecutorService methods
     * of an implementation.
     */ 
    static private 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.
     *
     * @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()));
    }

    /**
     * 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(),
                                    threadFactory, null));
    }

    /**
     * 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.
     *
     * @return the newly-created single-threaded Executor
     */
    public static ExecutorService newSingleThreadExecutor() {
        return new DelegatedExecutorService
            (new ThreadPoolExecutor(1, 1, 
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue()));
    }

    /**
     * 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(),
                                    threadFactory, null));
    }

    /**
     * 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.
     *
     * @return the newly created thread pool
     */
    public static ExecutorService newCachedThreadPool() {
        return new DelegatedExecutorService
            (new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                    60, TimeUnit.SECONDS,
                                    new SynchronousQueue()));
    }

    /**
     * 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(),
                                    threadFactory, null));
    }

    /**
     * Constructs a ScheduledExecutor.  A ScheduledExecutor is an
     * Executor which can schedule tasks to run at a given future
     * time, or to execute periodically.
     *
     * @param minThreads the minimum number of threads to keep in the
     * pool, even if they are idle.
     * @param maxThreads the maximum number of threads to allow in the
     * pool.
     * @param keepAliveTime when the number of threads is greater than
     * the minimum, this is the maximum time that excess idle threads
     * will wait for new tasks before terminating.
     * @param unit the time unit for the keepAliveTime
     * argument.
     * @return the newly created ScheduledExecutor
     */
    //    public static ScheduledExecutor newScheduledExecutor(int minThreads,
    //                                                         int maxThreads,
    //                                                         long keepAliveTime,
    //                                                         TimeUnit unit) {
    //        return new ScheduledExecutor(minThreads, maxThreads,
    //                                     keepAliveTime, unit);
    //    }

    /**
     * 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 CannotExecuteException if the 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 CannotExecuteException 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 CannotExecuteException if task cannot be scheduled for execution
     */
    public static void invoke(Executor executor, Runnable task)
            throws ExecutionException, InterruptedException {
        FutureTask ftask = new FutureTask(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 CannotExecuteException if task cannot be scheduled for execution
     */
    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();
    }
}
Revision:	1.2
Committed:	Tue May 27 18:14:40 2003 UTC (21 years ago) by dl
Branch:	MAIN
Changes since 1.1:	+106 -62 lines
Log Message:	re-check-in initial implementations
#	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
10	/**
11	* Factory and utility methods for the <tt>Executor</tt> classes
12	* defined in <tt>java.util.concurrent</tt>.
13	*
14	* <p>An Executor is a framework for executing Runnables. The
15	* Executor manages queueing and scheduling of tasks, and creation and
16	* teardown of threads. Depending on which concrete Executor class is
17	* being used, tasks may execute in a newly created thread, an
18	* existing task-execution thread, or the thread calling execute(),
19	* and may execute sequentially or concurrently.
20	*
21	* @since 1.5
22	* @see Executor
23	* @see ExecutorService
24	* @see Future
25	*
26	* @spec JSR-166
27	* @revised $Date: 2003/02/28 03:53:49 $
28	* @editor $Author: brian $
29	*/
30	public class Executors {
31
32	/**
33	* A wrapper class that exposes only the ExecutorService methods
34	* of an implementation.
35	*/
36	static private class DelegatedExecutorService implements ExecutorService {
37	private final ExecutorService e;
38	DelegatedExecutorService(ExecutorService executor) { e = executor; }
39	public void execute(Runnable command) { e.execute(command); }
40	public void shutdown() { e.shutdown(); }
41	public List shutdownNow() { return e.shutdownNow(); }
42	public boolean isShutdown() { return e.isShutdown(); }
43	public boolean isTerminated() { return e.isTerminated(); }
44	public boolean awaitTermination(long timeout, TimeUnit unit)
45	throws InterruptedException {
46	return e.awaitTermination(timeout, unit);
47	}
48	}
49
50	/**
51	* Creates a thread pool that reuses a fixed set of threads
52	* operating off a shared unbounded queue.
53	*
54	* @param nThreads the number of threads in the pool
55	* @return the newly created thread pool
56	*/
57	public static ExecutorService newFixedThreadPool(int nThreads) {
58	return new DelegatedExecutorService
59	(new ThreadPoolExecutor(nThreads, nThreads,
60	0L, TimeUnit.MILLISECONDS,
61	new LinkedBlockingQueue()));
62	}
63
64	/**
65	* Creates a thread pool that reuses a fixed set of threads
66	* operating off a shared unbounded queue, using the provided
67	* ThreadFactory to create new threads when needed.
68	*
69	* @param nThreads the number of threads in the pool
70	* @param threadfactory the factory to use when creating new threads
71	* @return the newly created thread pool
72	*/
73	public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
74	return new DelegatedExecutorService
75	(new ThreadPoolExecutor(nThreads, nThreads,
76	0L, TimeUnit.MILLISECONDS,
77	new LinkedBlockingQueue(),
78	threadFactory, null));
79	}
80
81	/**
82	* Creates an Executor that uses a single worker thread operating
83	* off an unbounded queue. (Note however that if this single
84	* thread terminates due to a failure during execution prior to
85	* shutdown, a new one will take its place if needed to execute
86	* subsequent tasks.) Tasks are guaranteed to execute
87	* sequentially, and no more than one task will be active at any
88	* given time.
89	*
90	* @return the newly-created single-threaded Executor
91	*/
92	public static ExecutorService newSingleThreadExecutor() {
93	return new DelegatedExecutorService
94	(new ThreadPoolExecutor(1, 1,
95	0L, TimeUnit.MILLISECONDS,
96	new LinkedBlockingQueue()));
97	}
98
99	/**
100	* Creates an Executor that uses a single worker thread operating
101	* off an unbounded queue, and uses the provided ThreadFactory to
102	* create new threads when needed.
103	* @param threadfactory the factory to use when creating new
104	* threads
105	*
106	* @return the newly-created single-threaded Executor
107	*/
108	public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {
109	return new DelegatedExecutorService
110	(new ThreadPoolExecutor(1, 1,
111	0L, TimeUnit.MILLISECONDS,
112	new LinkedBlockingQueue(),
113	threadFactory, null));
114	}
115
116	/**
117	* Creates a thread pool that creates new threads as needed, but
118	* will reuse previously constructed threads when they are
119	* available. These pools will typically improve the performance
120	* of programs that execute many short-lived asynchronous tasks.
121	* Calls to <tt>execute</tt> will reuse previously constructed
122	* threads if available. If no existing thread is available, a new
123	* thread will be created and added to the pool. Threads that have
124	* not been used for sixty seconds are terminated and removed from
125	* the cache. Thus, a pool that remains idle for long enough will
126	* not consume any resources.
127	*
128	* @return the newly created thread pool
129	*/
130	public static ExecutorService newCachedThreadPool() {
131	return new DelegatedExecutorService
132	(new ThreadPoolExecutor(0, Integer.MAX_VALUE,
133	60, TimeUnit.SECONDS,
134	new SynchronousQueue()));
135	}
136
137	/**
138	* Creates a thread pool that creates new threads as needed, but
139	* will reuse previously constructed threads when they are
140	* available, and uses the provided
141	* ThreadFactory to create new threads when needed.
142	* @param threadfactory the factory to use when creating new threads
143	* @return the newly created thread pool
144	*/
145	public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
146	return new DelegatedExecutorService
147	(new ThreadPoolExecutor(0, Integer.MAX_VALUE,
148	60, TimeUnit.SECONDS,
149	new SynchronousQueue(),
150	threadFactory, null));
151	}
152
153	/**
154	* Constructs a ScheduledExecutor. A ScheduledExecutor is an
155	* Executor which can schedule tasks to run at a given future
156	* time, or to execute periodically.
157	*
158	* @param minThreads the minimum number of threads to keep in the
159	* pool, even if they are idle.
160	* @param maxThreads the maximum number of threads to allow in the
161	* pool.
162	* @param keepAliveTime when the number of threads is greater than
163	* the minimum, this is the maximum time that excess idle threads
164	* will wait for new tasks before terminating.
165	* @param unit the time unit for the keepAliveTime
166	* argument.
167	* @return the newly created ScheduledExecutor
168	*/
169	// public static ScheduledExecutor newScheduledExecutor(int minThreads,
170	// int maxThreads,
171	// long keepAliveTime,
172	// TimeUnit unit) {
173	// return new ScheduledExecutor(minThreads, maxThreads,
174	// keepAliveTime, unit);
175	// }
176
177	/**
178	* Executes a Runnable task and returns a Future representing that
179	* task.
180	*
181	* @param executor the Executor to which the task will be submitted
182	* @param task the task to submit
183	* @param value the value which will become the return value of
184	* the task upon task completion
185	* @return a Future representing pending completion of the task
186	* @throws CannotExecuteException if the task cannot be scheduled
187	* for execution
188	*/
189	public static <T> Future<T> execute(Executor executor, Runnable task, T value) {
190	FutureTask<T> ftask = new FutureTask<T>(task, value);
191	executor.execute(ftask);
192	return ftask;
193	}
194
195	/**
196	* Executes a value-returning task and returns a Future
197	* representing the pending results of the task.
198	*
199	* @param executor the Executor to which the task will be submitted
200	* @param task the task to submit
201	* @return a Future representing pending completion of the task
202	* @throws CannotExecuteException if task cannot be scheduled for execution
203	*/
204	public static <T> Future<T> execute(Executor executor, Callable<T> task) {
205	FutureTask<T> ftask = new FutureTask<T>(task);
206	executor.execute(ftask);
207	return ftask;
208	}
209
210	/**
211	* Executes a Runnable task and blocks until it completes normally
212	* or throws an exception.
213	*
214	* @param executor the Executor to which the task will be submitted
215	* @param task the task to submit
216	* @throws CannotExecuteException if task cannot be scheduled for execution
217	*/
218	public static void invoke(Executor executor, Runnable task)
219	throws ExecutionException, InterruptedException {
220	FutureTask ftask = new FutureTask(task, Boolean.TRUE);
221	executor.execute(ftask);
222	ftask.get();
223	}
224
225	/**
226	* Executes a value-returning task and blocks until it returns a
227	* value or throws an exception.
228	*
229	* @param executor the Executor to which the task will be submitted
230	* @param task the task to submit
231	* @return a Future representing pending completion of the task
232	* @throws CannotExecuteException if task cannot be scheduled for execution
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	}