+ * Executor executor = anExecutor; + * executor.execute(new RunnableTask1()); + * executor.execute(new RunnableTask2()); + * ... + *+ * + * However, the Executor interface does not strictly + * require that execution be asynchronous. In the simplest case, an + * executor can run the submitted task immediately in the caller's + * thread: + * + *
+ * class DirectExecutor implements Executor {
+ * public void execute(Runnable r) {
+ * r.run();
+ * }
+ * }
+ *
+ * More typically, tasks are executed in some thread other
+ * than the caller's thread. The executor below spawns a new thread
+ * for each task.
+ *
+ *
+ * class ThreadPerTaskExecutor implements Executor {
+ * public void execute(Runnable r) {
+ * new Thread(r).start();
+ * }
+ * }
+ *
+ * Many Executor implementations impose some sort of
+ * limitation on how and when tasks are scheduled. The executor below
+ * serializes the submission of tasks to a second executor,
+ * illustrating a composite executor.
+ *
+ *
+ * class SerialExecutor implements Executor {
+ * final Queue<Runnable> tasks = new ArrayDeque<Runnable>();
+ * final Executor executor;
+ * Runnable active;
+ *
+ * SerialExecutor(Executor executor) {
+ * this.executor = executor;
+ * }
+ *
+ * public synchronized void execute(final Runnable r) {
+ * tasks.offer(new Runnable() {
+ * public void run() {
+ * try {
+ * r.run();
+ * } finally {
+ * scheduleNext();
+ * }
+ * }
+ * });
+ * if (active == null) {
+ * scheduleNext();
+ * }
+ * }
+ *
+ * protected synchronized void scheduleNext() {
+ * if ((active = tasks.poll()) != null) {
+ * executor.execute(active);
+ * }
+ * }
+ * }
+ *
+ * The Executor implementations provided in this package
+ * implement {@link ExecutorService}, which is a more extensive
+ * interface. The {@link ThreadPoolExecutor} class provides an
+ * extensible thread pool implementation. The {@link Executors} class
+ * provides convenient factory methods for these Executors.
+ *
+ * Memory consistency effects: Actions in a thread prior to + * submitting a {@code Runnable} object to an {@code Executor} + * happen-before + * its execution begins, perhaps in another thread. + * + * @since 1.5 + * @author Doug Lea + */ +public interface Executor { + + /** + * Executes the given command at some time in the future. The command + * may execute in a new thread, in a pooled thread, or in the calling + * thread, at the discretion of the Executor implementation. + * + * @param command the runnable task + * @throws RejectedExecutionException if this task cannot be + * accepted for execution. + * @throws NullPointerException if command is null + */ + void execute(Runnable command); +}