{@code
* Executor executor = anExecutor();
* executor.execute(new RunnableTask1());
* executor.execute(new RunnableTask2());
* ...}
*
* However, the {@code 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:
*
* {@code
* 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.
*
* {@code
* class ThreadPerTaskExecutor implements Executor {
* public void execute(Runnable r) {
* new Thread(r).start();
* }
* }}
*
* Many {@code 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.
*
* {@code
* class SerialExecutor implements Executor {
* final Queue tasks = new ArrayDeque<>();
* final Executor executor;
* Runnable active;
*
* SerialExecutor(Executor executor) {
* this.executor = executor;
* }
*
* public synchronized void execute(final Runnable r) {
* tasks.add(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 {@code 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 {@code 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); }