public interface ExecutorService extends Executor
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(java.lang.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.
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().
| Modifier and Type | Method and Description |
|---|---|
boolean |
awaitTermination(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.
|
<T> List<Future<T>> |
invokeAll(Collection<? extends Callable<T>> tasks)
Executes the given tasks, returning a list of Futures holding their status and results when all complete.
|
<T> List<Future<T>> |
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> T |
invokeAny(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> T |
invokeAny(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.
|
boolean |
isShutdown()
Returns true if this executor has been shut down.
|
boolean |
isTerminated()
Returns true if all tasks have completed following shut down.
|
void |
shutdown()
Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be
accepted.
|
List<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.
|
<T> Future<T> |
submit(Callable<T> task)
Submits a value-returning task for execution and returns a Future representing the pending results of the task.
|
Future<?> |
submit(Runnable task)
Submits a Runnable task for execution and returns a Future representing that task.
|
<T> Future<T> |
submit(Runnable task,
T result)
Submits a Runnable task for execution and returns a Future representing that task.
|
boolean awaitTermination(long timeout,
TimeUnit unit)
throws InterruptedException
timeout - the maximum time to waitunit - the time unit of the timeout argumentInterruptedException - if interrupted while waiting<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) throws InterruptedException
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.tasks - the collection of tasksInterruptedException - if interrupted while waiting, in which case unfinished tasks are cancelled.NullPointerException - if tasks or any of its elements are nullRejectedExecutionException - if any task cannot be scheduled for execution<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit) throws InterruptedException
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.tasks - the collection of taskstimeout - the maximum time to waitunit - the time unit of the timeout argumentInterruptedException - if interrupted while waiting, in which case unfinished tasks are cancelledNullPointerException - if tasks, any of its elements, or unit are nullRejectedExecutionException - if any task cannot be scheduled for execution<T> T invokeAny(Collection<? extends Callable<T>> tasks) throws InterruptedException, ExecutionException
tasks - the collection of tasksInterruptedException - if interrupted while waitingNullPointerException - if tasks or any element task subject to execution is nullIllegalArgumentException - if tasks is emptyExecutionException - if no task successfully completesRejectedExecutionException - if tasks cannot be scheduled for execution<T> T invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException
tasks - the collection of taskstimeout - the maximum time to waitunit - the time unit of the timeout argumentInterruptedException - if interrupted while waitingNullPointerException - if tasks, or unit, or any element task subject to execution is nullTimeoutException - if the given timeout elapses before any task successfully completesExecutionException - if no task successfully completesRejectedExecutionException - if tasks cannot be scheduled for executionboolean isShutdown()
boolean isTerminated()
void shutdown()
This method does not wait for previously submitted tasks to complete execution. Use awaitTermination to do that.
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
("modifyThread"), or the security manager's checkAccess method denies access.List<Runnable> shutdownNow()
This method does not wait for actively executing tasks to terminate. Use awaitTermination to 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.
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
("modifyThread"), or the security manager's checkAccess method denies access.<T> Future<T> submit(Callable<T> task)
If you would like to immediately block waiting for a task, you can use constructions of the form result = exec.submit(aCallable).get();
task - the task to submitRejectedExecutionException - if the task cannot be scheduled for executionNullPointerException - if the task is nullFuture<?> submit(Runnable task)
task - the task to submitRejectedExecutionException - if the task cannot be scheduled for executionNullPointerException - if the task is null<T> Future<T> submit(Runnable task, T result)
task - the task to submitresult - the result to returnRejectedExecutionException - if the task cannot be scheduled for executionNullPointerException - if the task is null