java.util.concurrent
Interface ExecutorService

All Superinterfaces:
Executor sample code for java.util.concurrent.Executor definition code for java.util.concurrent.Executor
All Known Subinterfaces:
ScheduledExecutorService sample code for java.util.concurrent.ScheduledExecutorService definition code for java.util.concurrent.ScheduledExecutorService
All Known Implementing Classes:
AbstractExecutorService sample code for java.util.concurrent.AbstractExecutorService definition code for java.util.concurrent.AbstractExecutorService , ScheduledThreadPoolExecutor sample code for java.util.concurrent.ScheduledThreadPoolExecutor definition code for java.util.concurrent.ScheduledThreadPoolExecutor , ThreadPoolExecutor sample code for java.util.concurrent.ThreadPoolExecutor definition code for java.util.concurrent.ThreadPoolExecutor

public interface ExecutorService
extends Executor sample code for java.util.concurrent.Executor definition code for java.util.concurrent.Executor

An Executor sample code for java.util.concurrent.Executor definition code for java.util.concurrent.Executor that provides methods to manage termination and methods that can produce a Future sample code for java.util.concurrent.Future definition code for java.util.concurrent.Future for tracking progress of one or more asynchronous tasks.

An ExecutorService can be shut down, which will cause it to stop accepting new tasks. After being shut down, the executor will eventually terminate, at which point no tasks are actively executing, no tasks are awaiting execution, and no new tasks can be submitted.

Method submit extends base method Executor.execute(java.lang.Runnable) sample code for java.util.concurrent.Executor.execute(java.lang.Runnable) definition code for java.util.concurrent.Executor.execute(java.lang.Runnable) by creating and returning a Future sample code for java.util.concurrent.Future definition code for java.util.concurrent.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 sample code for java.util.concurrent.ExecutorCompletionService definition code for java.util.concurrent.ExecutorCompletionService can be used to write customized variants of these methods.)

The Executors sample code for java.util.concurrent.Executors definition code for java.util.concurrent.Executors class provides factory methods for the executor services provided in this package.

Usage Example

Here is a sketch of a network service in which threads in a thread pool service incoming requests. It uses the preconfigured Executors.newFixedThreadPool(int) sample code for java.util.concurrent.Executors.newFixedThreadPool(int) definition code for java.util.concurrent.Executors.newFixedThreadPool(int) factory method:
 class NetworkService {
    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 serve() {
      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
    }
 }
 

Since:
1.5

Method Summary
 boolean awaitTermination sample code for java.util.concurrent.ExecutorService.awaitTermination(long, java.util.concurrent.TimeUnit) definition code for java.util.concurrent.ExecutorService.awaitTermination(long, java.util.concurrent.TimeUnit) (long timeout, TimeUnit sample code for java.util.concurrent.TimeUnit definition code for java.util.concurrent.TimeUnit  unit)
          Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first.
<T> List sample code for java.util.List definition code for java.util.List <Future sample code for java.util.concurrent.Future definition code for java.util.concurrent.Future <T>>
invokeAll sample code for java.util.concurrent.ExecutorService.invokeAll(java.util.Collection) definition code for java.util.concurrent.ExecutorService.invokeAll(java.util.Collection) (Collection sample code for java.util.Collection definition code for java.util.Collection <Callable sample code for java.util.concurrent.Callable definition code for java.util.concurrent.Callable <T>> tasks)
          Executes the given tasks, returning a list of Futures holding their status and results when all complete.
<T> List sample code for java.util.List definition code for java.util.List <Future sample code for java.util.concurrent.Future definition code for java.util.concurrent.Future <T>>
invokeAll sample code for java.util.concurrent.ExecutorService.invokeAll(java.util.Collection, long, java.util.concurrent.TimeUnit) definition code for java.util.concurrent.ExecutorService.invokeAll(java.util.Collection, long, java.util.concurrent.TimeUnit) (Collection sample code for java.util.Collection definition code for java.util.Collection <Callable sample code for java.util.concurrent.Callable definition code for java.util.concurrent.Callable <T>> tasks, long timeout, TimeUnit sample code for java.util.concurrent.TimeUnit definition code for java.util.concurrent.TimeUnit  unit)
          Executes the given tasks, returning a list of Futures holding their status and results when all complete or the timeout expires, whichever happens first.
<T> T
invokeAny sample code for java.util.concurrent.ExecutorService.invokeAny(java.util.Collection) definition code for java.util.concurrent.ExecutorService.invokeAny(java.util.Collection) (Collection sample code for java.util.Collection definition code for java.util.Collection <Callable sample code for java.util.concurrent.Callable definition code for java.util.concurrent.Callable <T>> tasks)
          Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do.
<T> T
invokeAny sample code for java.util.concurrent.ExecutorService.invokeAny(java.util.Collection, long, java.util.concurrent.TimeUnit) definition code for java.util.concurrent.ExecutorService.invokeAny(java.util.Collection, long, java.util.concurrent.TimeUnit) (Collection sample code for java.util.Collection definition code for java.util.Collection <Callable sample code for java.util.concurrent.Callable definition code for java.util.concurrent.Callable <T>> tasks, long timeout, TimeUnit sample code for java.util.concurrent.TimeUnit definition code for java.util.concurrent.TimeUnit  unit)
          Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do before the given timeout elapses.
 boolean isShutdown sample code for java.util.concurrent.ExecutorService.isShutdown() definition code for java.util.concurrent.ExecutorService.isShutdown() ()
          Returns true if this executor has been shut down.
 boolean isTerminated sample code for java.util.concurrent.ExecutorService.isTerminated() definition code for java.util.concurrent.ExecutorService.isTerminated() ()
          Returns true if all tasks have completed following shut down.
 void shutdown sample code for java.util.concurrent.ExecutorService.shutdown() definition code for java.util.concurrent.ExecutorService.shutdown() ()
          Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.
 List sample code for java.util.List definition code for java.util.List <Runnable sample code for java.lang.Runnable definition code for java.lang.Runnable > shutdownNow sample code for java.util.concurrent.ExecutorService.shutdownNow() definition code for java.util.concurrent.ExecutorService.shutdownNow() ()
          Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution.
<T> Future sample code for java.util.concurrent.Future definition code for java.util.concurrent.Future <T>
submit sample code for java.util.concurrent.ExecutorService.submit(java.util.concurrent.Callable) definition code for java.util.concurrent.ExecutorService.submit(java.util.concurrent.Callable) (Callable sample code for java.util.concurrent.Callable definition code for java.util.concurrent.Callable <T> task)
          Submits a value-returning task for execution and returns a Future representing the pending results of the task.
 Future sample code for java.util.concurrent.Future definition code for java.util.concurrent.Future <?> submit sample code for java.util.concurrent.ExecutorService.submit(java.lang.Runnable) definition code for java.util.concurrent.ExecutorService.submit(java.lang.Runnable) (Runnable sample code for java.lang.Runnable definition code for java.lang.Runnable  task)
          Submits a Runnable task for execution and returns a Future representing that task.
<T> Future sample code for java.util.concurrent.Future definition code for java.util.concurrent.Future <T>
submit sample code for java.util.concurrent.ExecutorService.submit(java.lang.Runnable, T) definition code for java.util.concurrent.ExecutorService.submit(java.lang.Runnable, T) (Runnable sample code for java.lang.Runnable definition code for java.lang.Runnable  task, T result)
          Submits a Runnable task for execution and returns a Future representing that task that will upon completion return the given result
 
Methods inherited from interface java.util.concurrent.Executor sample code for java.util.concurrent.Executor definition code for java.util.concurrent.Executor
execute sample code for java.util.concurrent.Executor.execute(java.lang.Runnable) definition code for java.util.concurrent.Executor.execute(java.lang.Runnable)
 

Method Detail

shutdown sample code for java.util.concurrent.ExecutorService.shutdown() definition code for java.util.concurrent.ExecutorService.shutdown()

void shutdown()
Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. Invocation has no additional effect if already shut down.

Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and shutting down this ExecutorService may manipulate threads that the caller is not permitted to modify because it does not hold RuntimePermission sample code for java.lang.RuntimePermission definition code for java.lang.RuntimePermission ("modifyThread"), or the security manager's checkAccess method denies access.

shutdownNow sample code for java.util.concurrent.ExecutorService.shutdownNow() definition code for java.util.concurrent.ExecutorService.shutdownNow()

List sample code for java.util.List definition code for java.util.List <Runnable sample code for java.lang.Runnable definition code for java.lang.Runnable > shutdownNow()
Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution.

There are no guarantees beyond best-effort attempts to stop processing actively executing tasks. For example, typical implementations will cancel via Thread.interrupt() sample code for java.lang.Thread.interrupt() definition code for java.lang.Thread.interrupt() , so if any tasks mask or fail to respond to interrupts, they may never terminate.

Returns:
list of tasks that never commenced execution
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and shutting down this ExecutorService may manipulate threads that the caller is not permitted to modify because it does not hold RuntimePermission sample code for java.lang.RuntimePermission definition code for java.lang.RuntimePermission ("modifyThread"), or the security manager's checkAccess method denies access.

isShutdown sample code for java.util.concurrent.ExecutorService.isShutdown() definition code for java.util.concurrent.ExecutorService.isShutdown()

boolean isShutdown()
Returns true if this executor has been shut down.

Returns:
true if this executor has been shut down

isTerminated sample code for java.util.concurrent.ExecutorService.isTerminated() definition code for java.util.concurrent.ExecutorService.isTerminated()

boolean isTerminated()
Returns true if all tasks have completed following shut down. Note that isTerminated is never true unless either shutdown or shutdownNow was called first.

Returns:
true if all tasks have completed following shut down

awaitTermination sample code for java.util.concurrent.ExecutorService.awaitTermination(long, java.util.concurrent.TimeUnit) definition code for java.util.concurrent.ExecutorService.awaitTermination(long, java.util.concurrent.TimeUnit)

boolean awaitTermination(long timeout,
                         TimeUnit sample code for java.util.concurrent.TimeUnit definition code for java.util.concurrent.TimeUnit  unit)
                         throws InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException 
Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first.

Parameters:
timeout - the maximum time to wait
unit - the time unit of the timeout argument
Returns:
true if this executor terminated and false if the timeout elapsed before termination
Throws:
InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException - if interrupted while waiting

submit sample code for java.util.concurrent.ExecutorService.<T>submit(java.util.concurrent.Callable<T>) definition code for java.util.concurrent.ExecutorService.<T>submit(java.util.concurrent.Callable<T>)

<T> Future sample code for java.util.concurrent.Future definition code for java.util.concurrent.Future <T> submit(Callable sample code for java.util.concurrent.Callable definition code for java.util.concurrent.Callable <T> task)
Submits a value-returning task for execution and returns a Future representing the pending results of the task.

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 sample code for java.util.concurrent.Executors definition code for java.util.concurrent.Executors class includes a set of methods that can convert some other common closure-like objects, for example, PrivilegedAction sample code for java.security.PrivilegedAction definition code for java.security.PrivilegedAction to Callable sample code for java.util.concurrent.Callable definition code for java.util.concurrent.Callable form so they can be submitted.

Parameters:
task - the task to submit
Returns:
a Future representing pending completion of the task
Throws:
RejectedExecutionException sample code for java.util.concurrent.RejectedExecutionException definition code for java.util.concurrent.RejectedExecutionException - if task cannot be scheduled for execution
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if task null

submit sample code for java.util.concurrent.ExecutorService.<T>submit(java.lang.Runnable, T) definition code for java.util.concurrent.ExecutorService.<T>submit(java.lang.Runnable, T)

<T> Future sample code for java.util.concurrent.Future definition code for java.util.concurrent.Future <T> submit(Runnable sample code for java.lang.Runnable definition code for java.lang.Runnable  task,
                     T result)
Submits a Runnable task for execution and returns a Future representing that task that will upon completion return the given result

Parameters:
task - the task to submit
result - the result to return
Returns:
a Future representing pending completion of the task, and whose get() method will return the given result upon completion.
Throws:
RejectedExecutionException sample code for java.util.concurrent.RejectedExecutionException definition code for java.util.concurrent.RejectedExecutionException - if task cannot be scheduled for execution
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if task null

submit sample code for java.util.concurrent.ExecutorService.submit(java.lang.Runnable) definition code for java.util.concurrent.ExecutorService.submit(java.lang.Runnable)

Future sample code for java.util.concurrent.Future definition code for java.util.concurrent.Future <?> submit(Runnable sample code for java.lang.Runnable definition code for java.lang.Runnable  task)
Submits a Runnable task for execution and returns a Future representing that task.

Parameters:
task - the task to submit
Returns:
a Future representing pending completion of the task, and whose get() method will return null upon completion.
Throws:
RejectedExecutionException sample code for java.util.concurrent.RejectedExecutionException definition code for java.util.concurrent.RejectedExecutionException - if task cannot be scheduled for execution
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if task null

invokeAll sample code for java.util.concurrent.ExecutorService.<T>invokeAll(java.util.Collection<java.util.concurrent.Callable<T>>) definition code for java.util.concurrent.ExecutorService.<T>invokeAll(java.util.Collection<java.util.concurrent.Callable<T>>)

<T> List sample code for java.util.List definition code for java.util.List <Future sample code for java.util.concurrent.Future definition code for java.util.concurrent.Future <T>> invokeAll(Collection sample code for java.util.Collection definition code for java.util.Collection <Callable sample code for java.util.concurrent.Callable definition code for java.util.concurrent.Callable <T>> tasks)
                          throws InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException 
Executes the given tasks, returning a list of Futures holding their status and results when all complete. Future.isDone() sample code for java.util.concurrent.Future.isDone() definition code for java.util.concurrent.Future.isDone() is true for each element of the returned list. Note that a completed task could have terminated either normally or by throwing an exception. The results of this method are undefined if the given collection is modified while this operation is in progress.

Parameters:
tasks - the collection of tasks
Returns:
A list of Futures representing the tasks, in the same sequential order as produced by the iterator for the given task list, each of which has completed.
Throws:
InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException - if interrupted while waiting, in which case unfinished tasks are cancelled.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if tasks or any of its elements are null
RejectedExecutionException sample code for java.util.concurrent.RejectedExecutionException definition code for java.util.concurrent.RejectedExecutionException - if any task cannot be scheduled for execution

invokeAll sample code for java.util.concurrent.ExecutorService.<T>invokeAll(java.util.Collection<java.util.concurrent.Callable<T>>, long, java.util.concurrent.TimeUnit) definition code for java.util.concurrent.ExecutorService.<T>invokeAll(java.util.Collection<java.util.concurrent.Callable<T>>, long, java.util.concurrent.TimeUnit)

<T> List sample code for java.util.List definition code for java.util.List <Future sample code for java.util.concurrent.Future definition code for java.util.concurrent.Future <T>> invokeAll(Collection sample code for java.util.Collection definition code for java.util.Collection <Callable sample code for java.util.concurrent.Callable definition code for java.util.concurrent.Callable <T>> tasks,
                              long timeout,
                              TimeUnit sample code for java.util.concurrent.TimeUnit definition code for java.util.concurrent.TimeUnit  unit)
                          throws InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException 
Executes the given tasks, returning a list of Futures holding their status and results when all complete or the timeout expires, whichever happens first. Future.isDone() sample code for java.util.concurrent.Future.isDone() definition code for java.util.concurrent.Future.isDone() is true for each element of the returned list. Upon return, tasks that have not completed are cancelled. Note that a completed task could have terminated either normally or by throwing an exception. The results of this method are undefined if the given collection is modified while this operation is in progress.

Parameters:
tasks - the collection of tasks
timeout - the maximum time to wait
unit - the time unit of the timeout argument
Returns:
A list of Futures representing the tasks, in the same sequential order as produced by the iterator for the given task list. If the operation did not time out, each task will have completed. If it did time out, some of these tasks will not have completed.
Throws:
InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException - if interrupted while waiting, in which case unfinished tasks are cancelled.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if tasks, any of its elements, or unit are null
RejectedExecutionException sample code for java.util.concurrent.RejectedExecutionException definition code for java.util.concurrent.RejectedExecutionException - if any task cannot be scheduled for execution

invokeAny sample code for java.util.concurrent.ExecutorService.<T>invokeAny(java.util.Collection<java.util.concurrent.Callable<T>>) definition code for java.util.concurrent.ExecutorService.<T>invokeAny(java.util.Collection<java.util.concurrent.Callable<T>>)

<T> T invokeAny(Collection sample code for java.util.Collection definition code for java.util.Collection <Callable sample code for java.util.concurrent.Callable definition code for java.util.concurrent.Callable <T>> tasks)
            throws InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException ,
                   ExecutionException sample code for java.util.concurrent.ExecutionException definition code for java.util.concurrent.ExecutionException 
Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do. Upon normal or exceptional return, tasks that have not completed are cancelled. The results of this method are undefined if the given collection is modified while this operation is in progress.

Parameters:
tasks - the collection of tasks
Returns:
The result returned by one of the tasks.
Throws:
InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException - if interrupted while waiting
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if tasks or any of its elements are null
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if tasks empty
ExecutionException sample code for java.util.concurrent.ExecutionException definition code for java.util.concurrent.ExecutionException - if no task successfully completes
RejectedExecutionException sample code for java.util.concurrent.RejectedExecutionException definition code for java.util.concurrent.RejectedExecutionException - if tasks cannot be scheduled for execution

invokeAny sample code for java.util.concurrent.ExecutorService.<T>invokeAny(java.util.Collection<java.util.concurrent.Callable<T>>, long, java.util.concurrent.TimeUnit) definition code for java.util.concurrent.ExecutorService.<T>invokeAny(java.util.Collection<java.util.concurrent.Callable<T>>, long, java.util.concurrent.TimeUnit)

<T> T invokeAny(Collection sample code for java.util.Collection definition code for java.util.Collection <Callable sample code for java.util.concurrent.Callable definition code for java.util.concurrent.Callable <T>> tasks,
                long timeout,
                TimeUnit sample code for java.util.concurrent.TimeUnit definition code for java.util.concurrent.TimeUnit  unit)
            throws InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException ,
                   ExecutionException sample code for java.util.concurrent.ExecutionException definition code for java.util.concurrent.ExecutionException ,
                   TimeoutException sample code for java.util.concurrent.TimeoutException definition code for java.util.concurrent.TimeoutException 
Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do before the given timeout elapses. Upon normal or exceptional return, tasks that have not completed are cancelled. The results of this method are undefined if the given collection is modified while this operation is in progress.

Parameters:
tasks - the collection of tasks
timeout - the maximum time to wait
unit - the time unit of the timeout argument
Returns:
The result returned by one of the tasks.
Throws:
InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException - if interrupted while waiting
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if tasks, any of its elements, or unit are null
TimeoutException sample code for java.util.concurrent.TimeoutException definition code for java.util.concurrent.TimeoutException - if the given timeout elapses before any task successfully completes
ExecutionException sample code for java.util.concurrent.ExecutionException definition code for java.util.concurrent.ExecutionException - if no task successfully completes
RejectedExecutionException sample code for java.util.concurrent.RejectedExecutionException definition code for java.util.concurrent.RejectedExecutionException - if tasks cannot be scheduled for execution