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: 2003/06/03 16:44:36 $
 * @editor $Author: dl $
 */
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<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, 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<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, 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<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, null));
    }

    /**
     * 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> FutureTask<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<Boolean> 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:	1.5
Committed:	Wed Jun 4 11:34:19 2003 UTC (21 years ago) by dl
Branch:	MAIN
Changes since 1.4:	+4 -5 lines
Log Message:	Minor documentation updates Remove remove(task) from ExecutorService, Add removablity to ScheduledExecutor tasks, Revert Executors.execute to return FutureTask
#	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: 2003/06/03 16:44:36 $
28	* @editor $Author: dl $
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<Runnable>()));
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<Runnable>(),
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<Runnable>()));
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<Runnable>(),
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<Runnable>()));
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<Runnable>(),
150	threadFactory, null));
151	}
152
153	/**
154	* Executes a Runnable task and returns a Future representing that
155	* task.
156	*
157	* @param executor the Executor to which the task will be submitted
158	* @param task the task to submit
159	* @param value the value which will become the return value of
160	* the task upon task completion
161	* @return a Future representing pending completion of the task
162	* @throws CannotExecuteException if the task cannot be scheduled
163	* for execution
164	*/
165	public static <T> Future<T> execute(Executor executor, Runnable task, T value) {
166	FutureTask<T> ftask = new FutureTask<T>(task, value);
167	executor.execute(ftask);
168	return ftask;
169	}
170
171	/**
172	* Executes a value-returning task and returns a Future
173	* representing the pending results of the task.
174	*
175	* @param executor the Executor to which the task will be submitted
176	* @param task the task to submit
177	* @return a Future representing pending completion of the task
178	* @throws CannotExecuteException if task cannot be scheduled for execution
179	*/
180	public static <T> FutureTask<T> execute(Executor executor, Callable<T> task) {
181	FutureTask<T> ftask = new FutureTask<T>(task);
182	executor.execute(ftask);
183	return ftask;
184	}
185
186	/**
187	* Executes a Runnable task and blocks until it completes normally
188	* or throws an exception.
189	*
190	* @param executor the Executor to which the task will be submitted
191	* @param task the task to submit
192	* @throws CannotExecuteException if task cannot be scheduled for execution
193	*/
194	public static void invoke(Executor executor, Runnable task)
195	throws ExecutionException, InterruptedException {
196	FutureTask<Boolean> ftask = new FutureTask(task, Boolean.TRUE);
197	executor.execute(ftask);
198	ftask.get();
199	}
200
201	/**
202	* Executes a value-returning task and blocks until it returns a
203	* value or throws an exception.
204	*
205	* @param executor the Executor to which the task will be submitted
206	* @param task the task to submit
207	* @return a Future representing pending completion of the task
208	* @throws CannotExecuteException if task cannot be scheduled for execution
209	*/
210	public static <T> T invoke(Executor executor, Callable<T> task)
211	throws ExecutionException, InterruptedException {
212	FutureTask<T> ftask = new FutureTask<T>(task);
213	executor.execute(ftask);
214	return ftask.get();
215	}
216	}