Java Doc for ExecutorService.java in  » 6.0-JDK-Core » Collections-Jar-Zip-Logging-regex » java » util » concurrent » Java Source Code / Java DocumentationJava Source Code and Java Documentation

An ExecutorService can be shut down, which will cause it to reject new tasks. Two different methods are provided for shutting down an ExecutorService. The ExecutorService.shutdown method will allow previously submitted tasks to execute before terminating, while the ExecutorService.shutdownNow method prevents waiting tasks from starting and attempts to stop currently executing tasks. Upon termination, an executor has no tasks actively executing, no tasks awaiting execution, and no new tasks can be submitted. An unused ExecutorService should be shut down to allow reclamation of its resources.

Method submit extends base method Executor.execute by creating and returning a Future that can be used to cancel execution and/or wait for completion. Methods invokeAny and invokeAll perform the most commonly useful forms of bulk execution, executing a collection of tasks and then waiting for at least one, or all, to complete. (Class ExecutorCompletionService can be used to write customized variants of these methods.)

The Executors class provides factory methods for the executor services provided in this package.

Usage Examples

 class NetworkService implements Runnable {
 private final ServerSocket serverSocket;
 private final ExecutorService pool;
 public NetworkService(int port, int poolSize)
 throws IOException {
 serverSocket = new ServerSocket(port);
 pool = Executors.newFixedThreadPool(poolSize);
 }
 public void run() { // run the service
 try {
 for (;;) {
 pool.execute(new Handler(serverSocket.accept()));
 }
 } catch (IOException ex) {
 pool.shutdown();
 }
 }
 }
 class Handler implements Runnable {
 private final Socket socket;
 Handler(Socket socket) { this.socket = socket; }
 public void run() {
 // read and service request on socket
 }
 }
 

 void shutdownAndAwaitTermination(ExecutorService pool) {
 pool.shutdown(); // Disable new tasks from being submitted
 try {
 // Wait a while for existing tasks to terminate
 if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {
 pool.shutdownNow(); // Cancel currently executing tasks
 // Wait a while for tasks to respond to being cancelled
 if (!pool.awaitTermination(60, TimeUnit.SECONDS))
 System.err.println("Pool did not terminate");
 }
 } catch (InterruptedException ie) {
 // (Re-)Cancel if current thread also interrupted
 pool.shutdownNow();
 // Preserve interrupt status
 Thread.currentThread().interrupt();
 }
 }
 

Memory consistency effects: Actions in a thread prior to the submission of a Runnable or Callable task to an ExecutorService happen-before any actions taken by that task, which in turn happen-before the result is retrieved via Future.get() .
since:
   1.5
author:
   Doug Lea

There are no guarantees beyond best-effort attempts to stop processing actively executing tasks.

There are no guarantees beyond best-effort attempts to stop processing actively executing tasks. For example, typical implementations will cancel via Thread.interrupt , so any task that fails to respond to interrupts may never terminate. list of tasks that never commenced execution
throws:
  SecurityException - if a security manager exists andshutting down this ExecutorService may manipulatethreads that the caller is not permitted to modifybecause it does not hold java.lang.RuntimePermission("modifyThread"),or the security manager's checkAccess methoddenies access.

If you would like to immediately block waiting for a task, you can use constructions of the form result = exec.submit(aCallable).get();

Note: The Executors class includes a set of methods that can convert some other common closure-like objects, for example, java.security.PrivilegedAction to Callable form so they can be submitted.
Parameters:
  task - the task to submit a Future representing pending completion of the task
throws:
  RejectedExecutionException - if the task cannot bescheduled for execution
throws:
  NullPointerException - if the task is null