Interface ExecutorService
- All Superinterfaces:
- AutoCloseable,- Executor
- All Known Subinterfaces:
- ScheduledExecutorService
- All Known Implementing Classes:
- AbstractExecutorService,- ForkJoinPool,- ScheduledThreadPoolExecutor,- ThreadPoolExecutor
Executor that provides methods to manage termination and
 methods that can produce a Future for tracking progress of
 one or more asynchronous tasks.
 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 shutdown()
 method will allow previously submitted tasks to execute before
 terminating, while the 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(Runnable) 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
Here is a sketch of a network service in which threads in a thread pool service incoming requests. It uses the preconfiguredExecutors.newFixedThreadPool(int) factory method:
  
 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
   }
 }
 An ExecutorService may also be established and closed
 (shutdown, blocking until terminated) as follows; illustrating with
 a different Executors factory method:
  
 try (ExecutorService e =  Executors.newWorkStealingPool()) {
   // submit or execute many tasks with e ...
 }
 Further customization is also possible. For example, the following
 method shuts down an ExecutorService in two phases, first
 by calling shutdown to reject incoming tasks, and then
 calling shutdownNow, if necessary, to cancel any lingering
 tasks:
  
 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 ex) {
     // (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
- 
Method SummaryModifier and TypeMethodDescriptionbooleanawaitTermination(long timeout, 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.default voidclose()Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.invokeAll(Collection<? extends Callable<T>> tasks) Executes the given tasks, returning a list of Futures holding their status and results when all complete.invokeAll(Collection<? extends Callable<T>> tasks, long timeout, 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> TinvokeAny(Collection<? extends 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> TinvokeAny(Collection<? extends Callable<T>> tasks, long timeout, 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.booleanReturnstrueif this executor has been shut down.booleanReturnstrueif all tasks have completed following shut down.voidshutdown()Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution.Future<?> Submits a Runnable task for execution and returns a Future representing that task.<T> Future<T> Submits a Runnable task for execution and returns a Future representing that task.<T> Future<T> Submits a value-returning task for execution and returns a Future representing the pending results of the task.
- 
Method Details- 
shutdownvoid 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.This method does not wait for previously submitted tasks to complete execution. Use awaitTerminationto do that.
- 
shutdownNowAttempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution.This method does not wait for actively executing tasks to terminate. Use awaitTerminationto do that.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.- Returns:
- list of tasks that never commenced execution
 
- 
isShutdownboolean isShutdown()Returnstrueif this executor has been shut down.- Returns:
- trueif this executor has been shut down
 
- 
isTerminatedboolean isTerminated()Returnstrueif all tasks have completed following shut down. Note thatisTerminatedis nevertrueunless eithershutdownorshutdownNowwas called first.- Returns:
- trueif all tasks have completed following shut down
 
- 
awaitTerminationBlocks 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:
- trueif this executor terminated and- falseif the timeout elapsed before termination
- Throws:
- InterruptedException- if interrupted while waiting
 
- 
submitSubmits a value-returning task for execution and returns a Future representing the pending results of the task. The Future'sgetmethod will return the task's result upon successful completion.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 Executorsclass includes a set of methods that can convert some other common closure-like objects, for example,PrivilegedActiontoCallableform so they can be submitted.- Type Parameters:
- T- the type of the task's result
- Parameters:
- task- the task to submit
- Returns:
- a Future representing pending completion of the task
- Throws:
- RejectedExecutionException- if the task cannot be scheduled for execution
- NullPointerException- if the task is null
 
- 
submitSubmits a Runnable task for execution and returns a Future representing that task. The Future'sgetmethod will return the given result upon successful completion.- Type Parameters:
- T- the type of the result
- Parameters:
- task- the task to submit
- result- the result to return
- Returns:
- a Future representing pending completion of the task
- Throws:
- RejectedExecutionException- if the task cannot be scheduled for execution
- NullPointerException- if the task is null
 
- 
submitSubmits a Runnable task for execution and returns a Future representing that task. The Future'sgetmethod will returnnullupon successful completion.- Parameters:
- task- the task to submit
- Returns:
- a Future representing pending completion of the task
- Throws:
- RejectedExecutionException- if the task cannot be scheduled for execution
- NullPointerException- if the task is null
 
- 
invokeAllExecutes the given tasks, returning a list of Futures holding their status and results when all complete.Future.isDone()istruefor 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.- Type Parameters:
- T- the type of the values returned from the tasks
- 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- if interrupted while waiting, in which case unfinished tasks are cancelled
- NullPointerException- if tasks or any of its elements are- null
- RejectedExecutionException- if any task cannot be scheduled for execution
 
- 
invokeAll<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit) throws 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()istruefor 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.- Type Parameters:
- T- the type of the values returned from the tasks
- 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- if interrupted while waiting, in which case unfinished tasks are cancelled
- NullPointerException- if tasks, any of its elements, or unit are- null
- RejectedExecutionException- if any task cannot be scheduled for execution
 
- 
invokeAny<T> T invokeAny(Collection<? extends Callable<T>> tasks) throws InterruptedException, 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.- Type Parameters:
- T- the type of the values returned from the tasks
- Parameters:
- tasks- the collection of tasks
- Returns:
- the result returned by one of the tasks
- Throws:
- InterruptedException- if interrupted while waiting
- NullPointerException- if tasks or any element task subject to execution is- null
- IllegalArgumentException- if tasks is empty
- ExecutionException- if no task successfully completes
- RejectedExecutionException- if tasks cannot be scheduled for execution
 
- 
invokeAny<T> T invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, 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.- Type Parameters:
- T- the type of the values returned from the tasks
- 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- if interrupted while waiting
- NullPointerException- if tasks, or unit, or any element task subject to execution is- null
- TimeoutException- if the given timeout elapses before any task successfully completes
- ExecutionException- if no task successfully completes
- RejectedExecutionException- if tasks cannot be scheduled for execution
 
- 
closedefault void close()Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. This method waits until all tasks have completed execution and the executor has terminated.If interrupted while waiting, this method stops all executing tasks as if by invoking shutdownNow(). It then continues to wait until all actively executing tasks have completed. Tasks that were awaiting execution are not executed. The interrupt status will be re-asserted before this method returns.If already terminated, invoking this method has no effect. - Specified by:
- closein interface- AutoCloseable
- Implementation Requirements:
- The default implementation invokes shutdown()and waits for tasks to complete execution withawaitTermination.
- Since:
- 19
 
 
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