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: 2003/05/29 13:49:24 $
 * @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 remove(Runnable r) { return e.remove(r) ; }
        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 CancellableTask that allows cancellation.
     * @throws CannotExecuteException if the task cannot be scheduled
     * for execution
     */
    public static CancellableTask execute(Executor executor, Runnable task) {
        CancellableTask ftask = new CancellableTask(task);
        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:	1.4
Committed:	Tue Jun 3 16:44:36 2003 UTC (21 years ago) by dl
Branch:	MAIN
Changes since 1.3:	+7 -30 lines
Log Message:	New ScheduledExecutor; CancellableTask
#	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			* <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	dl	1.2	* @see ExecutorService
24	tim	1.1	* @see Future
25			*
26			* @spec JSR-166
27	dl	1.4	* @revised $Date: 2003/05/29 13:49:24 $
28	dl	1.3	* @editor $Author: dl $
29	tim	1.1	*/
30			public class Executors {
31
32			/**
33	dl	1.2	* 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	dl	1.4	public boolean remove(Runnable r) { return e.remove(r) ; }
45	dl	1.2	public boolean awaitTermination(long timeout, TimeUnit unit)
46			throws InterruptedException {
47			return e.awaitTermination(timeout, unit);
48			}
49			}
50
51			/**
52	tim	1.1	* Creates a thread pool that reuses a fixed set of threads
53			* operating off a shared unbounded queue.
54			*
55			* @param nThreads the number of threads in the pool
56			* @return the newly created thread pool
57			*/
58	dl	1.2	public static ExecutorService newFixedThreadPool(int nThreads) {
59			return new DelegatedExecutorService
60			(new ThreadPoolExecutor(nThreads, nThreads,
61			0L, TimeUnit.MILLISECONDS,
62	dl	1.3	new LinkedBlockingQueue<Runnable>()));
63	dl	1.2	}
64
65			/**
66			* Creates a thread pool that reuses a fixed set of threads
67			* operating off a shared unbounded queue, using the provided
68			* ThreadFactory to create new threads when needed.
69			*
70			* @param nThreads the number of threads in the pool
71			* @param threadfactory the factory to use when creating new threads
72			* @return the newly created thread pool
73			*/
74			public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
75			return new DelegatedExecutorService
76			(new ThreadPoolExecutor(nThreads, nThreads,
77			0L, TimeUnit.MILLISECONDS,
78	dl	1.3	new LinkedBlockingQueue<Runnable>(),
79	dl	1.2	threadFactory, null));
80			}
81
82			/**
83			* Creates an Executor that uses a single worker thread operating
84			* off an unbounded queue. (Note however that if this single
85			* thread terminates due to a failure during execution prior to
86			* shutdown, a new one will take its place if needed to execute
87			* subsequent tasks.) Tasks are guaranteed to execute
88			* sequentially, and no more than one task will be active at any
89			* given time.
90			*
91			* @return the newly-created single-threaded Executor
92			*/
93			public static ExecutorService newSingleThreadExecutor() {
94			return new DelegatedExecutorService
95			(new ThreadPoolExecutor(1, 1,
96			0L, TimeUnit.MILLISECONDS,
97	dl	1.3	new LinkedBlockingQueue<Runnable>()));
98	dl	1.2	}
99
100			/**
101			* Creates an Executor that uses a single worker thread operating
102			* off an unbounded queue, and uses the provided ThreadFactory to
103			* create new threads when needed.
104			* @param threadfactory the factory to use when creating new
105			* threads
106			*
107			* @return the newly-created single-threaded Executor
108			*/
109			public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {
110			return new DelegatedExecutorService
111			(new ThreadPoolExecutor(1, 1,
112			0L, TimeUnit.MILLISECONDS,
113	dl	1.3	new LinkedBlockingQueue<Runnable>(),
114	dl	1.2	threadFactory, null));
115	tim	1.1	}
116
117			/**
118			* Creates a thread pool that creates new threads as needed, but
119			* will reuse previously constructed threads when they are
120			* available. These pools will typically improve the performance
121			* of programs that execute many short-lived asynchronous tasks.
122			* Calls to <tt>execute</tt> will reuse previously constructed
123			* threads if available. If no existing thread is available, a new
124			* thread will be created and added to the pool. Threads that have
125			* not been used for sixty seconds are terminated and removed from
126			* the cache. Thus, a pool that remains idle for long enough will
127			* not consume any resources.
128			*
129			* @return the newly created thread pool
130			*/
131	dl	1.2	public static ExecutorService newCachedThreadPool() {
132			return new DelegatedExecutorService
133			(new ThreadPoolExecutor(0, Integer.MAX_VALUE,
134			60, TimeUnit.SECONDS,
135	dl	1.3	new SynchronousQueue<Runnable>()));
136	tim	1.1	}
137
138			/**
139	dl	1.2	* Creates a thread pool that creates new threads as needed, but
140			* will reuse previously constructed threads when they are
141			* available, and uses the provided
142			* ThreadFactory to create new threads when needed.
143			* @param threadfactory the factory to use when creating new threads
144	tim	1.1	* @return the newly created thread pool
145			*/
146	dl	1.2	public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
147			return new DelegatedExecutorService
148			(new ThreadPoolExecutor(0, Integer.MAX_VALUE,
149			60, TimeUnit.SECONDS,
150	dl	1.3	new SynchronousQueue<Runnable>(),
151	dl	1.2	threadFactory, null));
152	tim	1.1	}
153
154			/**
155			* Executes a Runnable task and returns a Future representing that
156			* task.
157			*
158			* @param executor the Executor to which the task will be submitted
159			* @param task the task to submit
160			* @param value the value which will become the return value of
161			* the task upon task completion
162	dl	1.4	* @return a CancellableTask that allows cancellation.
163	tim	1.1	* @throws CannotExecuteException if the task cannot be scheduled
164			* for execution
165			*/
166	dl	1.4	public static CancellableTask execute(Executor executor, Runnable task) {
167			CancellableTask ftask = new CancellableTask(task);
168	tim	1.1	executor.execute(ftask);
169			return ftask;
170			}
171
172			/**
173			* Executes a value-returning task and returns a Future
174			* representing the pending results of the task.
175			*
176			* @param executor the Executor to which the task will be submitted
177			* @param task the task to submit
178			* @return a Future representing pending completion of the task
179			* @throws CannotExecuteException if task cannot be scheduled for execution
180			*/
181	dl	1.4	public static <T> FutureTask<T> execute(Executor executor, Callable<T> task) {
182	tim	1.1	FutureTask<T> ftask = new FutureTask<T>(task);
183			executor.execute(ftask);
184			return ftask;
185			}
186
187			/**
188			* Executes a Runnable task and blocks until it completes normally
189			* or throws an exception.
190			*
191			* @param executor the Executor to which the task will be submitted
192			* @param task the task to submit
193			* @throws CannotExecuteException if task cannot be scheduled for execution
194			*/
195			public static void invoke(Executor executor, Runnable task)
196			throws ExecutionException, InterruptedException {
197	dl	1.4	FutureTask<Boolean> ftask = new FutureTask(task, Boolean.TRUE);
198	tim	1.1	executor.execute(ftask);
199			ftask.get();
200			}
201
202			/**
203			* Executes a value-returning task and blocks until it returns a
204			* value 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			* @return a Future representing pending completion of the task
209			* @throws CannotExecuteException if task cannot be scheduled for execution
210			*/
211			public static <T> T invoke(Executor executor, Callable<T> task)
212			throws ExecutionException, InterruptedException {
213			FutureTask<T> ftask = new FutureTask<T>(task);
214			executor.execute(ftask);
215			return ftask.get();
216			}
217			}