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>.
 *
 * @since 1.5
 * @see Executor
 * @see ExecutorService
 * @see Future
 *
 * @spec JSR-166
 * @revised $Date: 2003/06/18 10:18:36 $
 * @editor $Author: jozart $
 * @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.
     *
     * @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 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> 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 RejectedExecutionException 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 RejectedExecutionException if task cannot be scheduled
     * for execution
     * @throws InterruptedException if interrupted while waiting for
     * completion
     */
    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:	1.12
Committed:	Tue Jun 24 14:34:48 2003 UTC (20 years, 11 months ago) by dl
Branch:	MAIN
CVS Tags:	JSR166_PRELIMINARY_TEST_RELEASE_2
Changes since 1.11:	+8 -5 lines
Log Message:	Added missing javadoc tags; minor reformatting
#	User	Rev	Content
1	tim	1.1	/*
2	dl	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	tim	1.1	*/
6
7			package java.util.concurrent;
8	dl	1.2	import java.util.*;
9	tim	1.1
10			/**
11	dl	1.2	* Factory and utility methods for the <tt>Executor</tt> classes
12			* defined in <tt>java.util.concurrent</tt>.
13	tim	1.1	*
14			* @since 1.5
15			* @see Executor
16	dl	1.2	* @see ExecutorService
17	tim	1.1	* @see Future
18			*
19			* @spec JSR-166
20	dl	1.12	* @revised $Date: 2003/06/18 10:18:36 $
21			* @editor $Author: jozart $
22			* @author Doug Lea
23	tim	1.1	*/
24			public class Executors {
25
26			/**
27	dl	1.2	* A wrapper class that exposes only the ExecutorService methods
28			* of an implementation.
29	tim	1.6	*/
30	jozart	1.11	private static class DelegatedExecutorService implements ExecutorService {
31	dl	1.2	private final ExecutorService e;
32			DelegatedExecutorService(ExecutorService executor) { e = executor; }
33			public void execute(Runnable command) { e.execute(command); }
34			public void shutdown() { e.shutdown(); }
35			public List shutdownNow() { return e.shutdownNow(); }
36			public boolean isShutdown() { return e.isShutdown(); }
37			public boolean isTerminated() { return e.isTerminated(); }
38			public boolean awaitTermination(long timeout, TimeUnit unit)
39			throws InterruptedException {
40			return e.awaitTermination(timeout, unit);
41			}
42			}
43
44			/**
45	tim	1.1	* Creates a thread pool that reuses a fixed set of threads
46			* operating off a shared unbounded queue.
47			*
48			* @param nThreads the number of threads in the pool
49			* @return the newly created thread pool
50			*/
51	dl	1.2	public static ExecutorService newFixedThreadPool(int nThreads) {
52			return new DelegatedExecutorService
53			(new ThreadPoolExecutor(nThreads, nThreads,
54			0L, TimeUnit.MILLISECONDS,
55	dl	1.3	new LinkedBlockingQueue<Runnable>()));
56	dl	1.2	}
57
58			/**
59			* Creates a thread pool that reuses a fixed set of threads
60			* operating off a shared unbounded queue, using the provided
61			* ThreadFactory to create new threads when needed.
62			*
63			* @param nThreads the number of threads in the pool
64	dl	1.12	* @param threadFactory the factory to use when creating new threads
65	dl	1.2	* @return the newly created thread pool
66			*/
67			public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
68			return new DelegatedExecutorService
69			(new ThreadPoolExecutor(nThreads, nThreads,
70			0L, TimeUnit.MILLISECONDS,
71	dl	1.3	new LinkedBlockingQueue<Runnable>(),
72	dl	1.2	threadFactory, null));
73			}
74
75			/**
76			* Creates an Executor that uses a single worker thread operating
77			* off an unbounded queue. (Note however that if this single
78			* thread terminates due to a failure during execution prior to
79			* shutdown, a new one will take its place if needed to execute
80			* subsequent tasks.) Tasks are guaranteed to execute
81			* sequentially, and no more than one task will be active at any
82			* given time.
83			*
84			* @return the newly-created single-threaded Executor
85			*/
86			public static ExecutorService newSingleThreadExecutor() {
87			return new DelegatedExecutorService
88	tim	1.6	(new ThreadPoolExecutor(1, 1,
89	dl	1.2	0L, TimeUnit.MILLISECONDS,
90	dl	1.3	new LinkedBlockingQueue<Runnable>()));
91	dl	1.2	}
92
93			/**
94			* Creates an Executor that uses a single worker thread operating
95			* off an unbounded queue, and uses the provided ThreadFactory to
96			* create new threads when needed.
97	dl	1.12	* @param threadFactory the factory to use when creating new
98	dl	1.2	* threads
99			*
100			* @return the newly-created single-threaded Executor
101			*/
102			public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {
103			return new DelegatedExecutorService
104	tim	1.6	(new ThreadPoolExecutor(1, 1,
105	dl	1.2	0L, TimeUnit.MILLISECONDS,
106	dl	1.3	new LinkedBlockingQueue<Runnable>(),
107	dl	1.2	threadFactory, null));
108	tim	1.1	}
109
110			/**
111			* Creates a thread pool that creates new threads as needed, but
112			* will reuse previously constructed threads when they are
113			* available. These pools will typically improve the performance
114			* of programs that execute many short-lived asynchronous tasks.
115			* Calls to <tt>execute</tt> will reuse previously constructed
116			* threads if available. If no existing thread is available, a new
117			* thread will be created and added to the pool. Threads that have
118			* not been used for sixty seconds are terminated and removed from
119			* the cache. Thus, a pool that remains idle for long enough will
120			* not consume any resources.
121			*
122			* @return the newly created thread pool
123			*/
124	dl	1.2	public static ExecutorService newCachedThreadPool() {
125			return new DelegatedExecutorService
126			(new ThreadPoolExecutor(0, Integer.MAX_VALUE,
127			60, TimeUnit.SECONDS,
128	dl	1.3	new SynchronousQueue<Runnable>()));
129	tim	1.1	}
130
131			/**
132	dl	1.2	* Creates a thread pool that creates new threads as needed, but
133			* will reuse previously constructed threads when they are
134	tim	1.6	* available, and uses the provided
135	dl	1.2	* ThreadFactory to create new threads when needed.
136	dl	1.12	* @param threadFactory the factory to use when creating new threads
137	tim	1.1	* @return the newly created thread pool
138			*/
139	dl	1.2	public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
140			return new DelegatedExecutorService
141			(new ThreadPoolExecutor(0, Integer.MAX_VALUE,
142			60, TimeUnit.SECONDS,
143	dl	1.3	new SynchronousQueue<Runnable>(),
144	dl	1.2	threadFactory, null));
145	tim	1.1	}
146
147			/**
148			* Executes a Runnable task and returns a Future representing that
149			* task.
150			*
151			* @param executor the Executor to which the task will be submitted
152			* @param task the task to submit
153			* @param value the value which will become the return value of
154			* the task upon task completion
155	dl	1.5	* @return a Future representing pending completion of the task
156	jozart	1.9	* @throws RejectedExecutionException if task cannot be scheduled
157	tim	1.1	* for execution
158			*/
159	dl	1.5	public static <T> Future<T> execute(Executor executor, Runnable task, T value) {
160	dl	1.10	FutureTask<T> ftask = new FutureTask<T>(task, value);
161	tim	1.1	executor.execute(ftask);
162			return ftask;
163			}
164
165			/**
166			* Executes a value-returning task and returns a Future
167			* representing the pending results of the task.
168			*
169			* @param executor the Executor to which the task will be submitted
170			* @param task the task to submit
171			* @return a Future representing pending completion of the task
172	jozart	1.9	* @throws RejectedExecutionException if task cannot be scheduled
173			* for execution
174	tim	1.1	*/
175	dl	1.4	public static <T> FutureTask<T> execute(Executor executor, Callable<T> task) {
176	dl	1.10	FutureTask<T> ftask = new FutureTask<T>(task);
177	tim	1.1	executor.execute(ftask);
178			return ftask;
179			}
180
181			/**
182			* Executes a Runnable task and blocks until it completes normally
183			* or throws an exception.
184			*
185			* @param executor the Executor to which the task will be submitted
186			* @param task the task to submit
187	jozart	1.9	* @throws RejectedExecutionException if task cannot be scheduled
188			* for execution
189	tim	1.1	*/
190			public static void invoke(Executor executor, Runnable task)
191			throws ExecutionException, InterruptedException {
192	dl	1.4	FutureTask<Boolean> ftask = new FutureTask(task, Boolean.TRUE);
193	tim	1.1	executor.execute(ftask);
194			ftask.get();
195			}
196
197			/**
198			* Executes a value-returning task and blocks until it returns a
199			* value or throws an exception.
200			*
201			* @param executor the Executor to which the task will be submitted
202			* @param task the task to submit
203			* @return a Future representing pending completion of the task
204	jozart	1.9	* @throws RejectedExecutionException if task cannot be scheduled
205			* for execution
206	dl	1.12	* @throws InterruptedException if interrupted while waiting for
207			* completion
208	tim	1.1	*/
209			public static <T> T invoke(Executor executor, Callable<T> task)
210			throws ExecutionException, InterruptedException {
211			FutureTask<T> ftask = new FutureTask<T>(task);
212			executor.execute(ftask);
213			return ftask.get();
214	tim	1.6	}
215
216	tim	1.1	}