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java.util.concurrent
Interface ExecutorService
-
All Superinterfaces:
-
Executor
-
All Known Subinterfaces:
-
ScheduledExecutorService
-
All Known Implementing Classes:
-
AbstractExecutorService
,
ScheduledThreadPoolExecutor
,
ThreadPoolExecutor
-
public interface ExecutorService
- extends Executor
An
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 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)
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 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)
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
}
}
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 Summary
|
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. |
|
invokeAll
(
Collection
<? extends
Callable
<
Callable
<T>> tasks)
Executes the given tasks, returning a list of Futures holding their status and results when all complete. |
|
invokeAll
(
Collection
<? extends
Callable
<
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. |
|
invokeAny
(
Collection
<? extends
Callable
<
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. |
|
invokeAny
(
Collection
<? extends
Callable
<
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. |
|
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
Submits a Runnable task for execution and returns a Future representing that task. |
|
submit
(
Runnable
task, T result)
Submits a Runnable task for execution and returns a Future representing that
task.
task that will upon completion return the given result
|
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
- 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.
shutdownNow
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.
There are no guarantees beyond best-effort attempts to stop processing actively executing tasks. For example, typical implementations will cancel via
Thread.interrupt()
, so
if
any
task that fails
tasks mask or fail
to respond to
interrupts
interrupts, they
may never terminate.
-
-
-
Returns:
-
list of tasks that never commenced execution
-
Throws:
-
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.
isShutdown
boolean isShutdown()
-
Returns
true
if this executor has been shut down.
-
-
-
Returns:
-
true
if this executor has been shut down
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
boolean awaitTermination(long timeout,
TimeUnit unit)
throws 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
- if interrupted while waiting
submit
<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.
The Future's
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.
-
-
-
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
submit
<T> Future<T> submit(Runnable task,
T result)
-
Submits a Runnable task for execution and returns a Future representing that
task. The Future's
get
method
task that
will
upon completion
return the given result
upon successful completion.
-
-
-
Parameters:
-
task - the task to submit
-
result - the result to return
-
Returns:
-
a Future representing pending completion of the task
a Future representing pending completion of the task, and whose
get()
method will return the given result upon completion.
-
Throws:
-
RejectedExecutionException
- if
the
task cannot be scheduled for execution -
NullPointerException
- if
the
task
is
null
submit
Future<?> submit(Runnable task)
-
Submits a Runnable task for execution and returns a Future representing that task.
The Future's
get
method will return
null
upon successful completion.
-
-
-
Parameters:
-
task - the task to submit
-
Returns:
-
a Future representing pending completion of the task
a Future representing pending completion of the task, and whose
get()
method will return
null
upon completion.
-
Throws:
-
RejectedExecutionException
- if
the
task cannot be scheduled for execution -
NullPointerException
- if
the
task
is
null
invokeAll
<T> List<Future<T>> invokeAll(Collection
<? extends
Callable
< 
Callable<T>> tasks)
throws InterruptedException
-
Executes the given tasks, returning a list of Futures holding their status and results when all complete.
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
- 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
< 
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()
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
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
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
< 
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.
-
-
-
Parameters:
-
tasks - the collection of tasks
-
Returns:
-
the
The
result returned by one of the
tasks
tasks.
-
Throws:
-
InterruptedException
- if interrupted while waiting
-
NullPointerException
- if tasks or any of its elements are
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
< 
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.
-
-
-
Parameters:
-
tasks - the collection of tasks
-
timeout - the maximum time to wait
-
unit - the time unit of the timeout argument
-
Returns:
-
the
The
result returned by one of the tasks. -
Throws:
-
InterruptedException
- if interrupted while waiting
-
NullPointerException
- if tasks, any of its elements, or unit are
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