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1: /* 2: * Written by Doug Lea with assistance from members of JCP JSR-166 3: * Expert Group and released to the public domain, as explained at 4: * http://creativecommons.org/licenses/publicdomain 5: */ 6: 7: package java.util.concurrent; 8: 9: /** 10: * An object that executes submitted {@link Runnable} tasks. This 11: * interface provides a way of decoupling task submission from the 12: * mechanics of how each task will be run, including details of thread 13: * use, scheduling, etc. An <tt>Executor</tt> is normally used 14: * instead of explicitly creating threads. For example, rather than 15: * invoking <tt>new Thread(new(RunnableTask())).start()</tt> for each 16: * of a set of tasks, you might use: 17: * 18: * <pre> 19: * Executor executor = <em>anExecutor</em>; 20: * executor.execute(new RunnableTask1()); 21: * executor.execute(new RunnableTask2()); 22: * ... 23: * </pre> 24: * 25: * However, the <tt>Executor</tt> interface does not strictly 26: * require that execution be asynchronous. In the simplest case, an 27: * executor can run the submitted task immediately in the caller's 28: * thread: 29: * 30: * <pre> 31: * class DirectExecutor implements Executor { 32: * public void execute(Runnable r) { 33: * r.run(); 34: * } 35: * }</pre> 36: * 37: * More typically, tasks are executed in some thread other 38: * than the caller's thread. The executor below spawns a new thread 39: * for each task. 40: * 41: * <pre> 42: * class ThreadPerTaskExecutor implements Executor { 43: * public void execute(Runnable r) { 44: * new Thread(r).start(); 45: * } 46: * }</pre> 47: * 48: * Many <tt>Executor</tt> implementations impose some sort of 49: * limitation on how and when tasks are scheduled. The executor below 50: * serializes the submission of tasks to a second executor, 51: * illustrating a composite executor. 52: * 53: * <pre> 54: * class SerialExecutor implements Executor { 55: * final Queue<Runnable> tasks = new ArrayDeque<Runnable>(); 56: * final Executor executor; 57: * Runnable active; 58: * 59: * SerialExecutor(Executor executor) { 60: * this.executor = executor; 61: * } 62: * 63: * public synchronized void execute(final Runnable r) { 64: * tasks.offer(new Runnable() { 65: * public void run() { 66: * try { 67: * r.run(); 68: * } finally { 69: * scheduleNext(); 70: * } 71: * } 72: * }); 73: * if (active == null) { 74: * scheduleNext(); 75: * } 76: * } 77: * 78: * protected synchronized void scheduleNext() { 79: * if ((active = tasks.poll()) != null) { 80: * executor.execute(active); 81: * } 82: * } 83: * }</pre> 84: * 85: * The <tt>Executor</tt> implementations provided in this package 86: * implement {@link ExecutorService}, which is a more extensive 87: * interface. The {@link ThreadPoolExecutor} class provides an 88: * extensible thread pool implementation. The {@link Executors} class 89: * provides convenient factory methods for these Executors. 90: * 91: * <p>Memory consistency effects: Actions in a thread prior to 92: * submitting a {@code Runnable} object to an {@code Executor} 93: * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> 94: * its execution begins, perhaps in another thread. 95: * 96: * @since 1.5 97: * @author Doug Lea 98: */ 99: public interface Executor { 100: 101: /** 102: * Executes the given command at some time in the future. The command 103: * may execute in a new thread, in a pooled thread, or in the calling 104: * thread, at the discretion of the <tt>Executor</tt> implementation. 105: * 106: * @param command the runnable task 107: * @throws RejectedExecutionException if this task cannot be 108: * accepted for execution. 109: * @throws NullPointerException if command is null 110: */ 111: void execute(Runnable command); 112: }
GNU Classpath (0.98) |