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(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.
Executors.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
}
}
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 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.
|
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.boolean isShutdown()
true if this executor has been shut down.true if this executor has been shut downboolean isTerminated()
true if all tasks have completed following shut down.
Note that isTerminated is never true unless
either shutdown or shutdownNow was called first.true if all tasks have completed following shut downboolean awaitTermination(long timeout,
TimeUnit unit)
throws InterruptedException
timeout - the maximum time to waitunit - the time unit of the timeout argumenttrue if this executor terminated and
false if the timeout elapsed before terminationInterruptedException - if interrupted while waiting<T> Future<T> submit(Callable<T> task)
get method 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 Executors class includes a set of methods
that can convert some other common closure-like objects,
for example, PrivilegedAction to
Callable form so they can be submitted.
T - the type of the task's resulttask - 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)
get method will
return the given result upon successful completion.T - the type of the resulttask - the task to submitresult - the result to returnRejectedExecutionException - if the task cannot be
scheduled for executionNullPointerException - if the task is nullFuture<?> submit(Runnable task)
get method will
return null upon successful completion.task - the task to submitRejectedExecutionException - if the task cannot be
scheduled for executionNullPointerException - if the task is null<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.T - the type of the values returned from the taskstasks - the collection of tasksInterruptedException - if interrupted while waiting, in
which case unfinished tasks are cancelledNullPointerException - 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.T - the type of the values returned from the taskstasks - 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
T - the type of the values returned from the taskstasks - 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
T - the type of the values returned from the taskstasks - 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 execution Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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