| java.util.concurrent.ExecutorService |
 Known Indirect Subclasses
|
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 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 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.
Developers
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().
| Public Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Blocks until all tasks have completed execution after a shutdown
request, or the timeout occurs, or the current thread is
interrupted, whichever happens first.
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Executes the given tasks, returning a list of Futures holding
their status and results when all complete.
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Executes the given tasks, returning a list of Futures holding
their status and results
when all complete or the timeout expires, whichever happens first.
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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.
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Executes the given tasks, returning the result
of one that has completed successfully (i.e., without throwing
an exception), if any do.
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Returns
true if this executor has been shut down.
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Returns
true if all tasks have completed following shut down.
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Initiates an orderly shutdown in which previously submitted
tasks are executed, but no new tasks will be accepted.
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Attempts to stop all actively executing tasks, halts the
processing of waiting tasks, and returns a list of the tasks
that were awaiting execution.
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Submits a Runnable task for execution and returns a Future
representing that task.
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Submits a value-returning task for execution and returns a
Future representing the pending results of the task.
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Submits a Runnable task for execution and returns a Future
representing that task.
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[Expand]
Inherited Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
|
From interface
java.util.concurrent.Executor
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Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first.
| timeout | the maximum time to wait |
|---|---|
| unit | the time unit of the timeout argument |
true if this executor terminated and
false if the timeout elapsed before termination| InterruptedException | if interrupted while waiting |
|---|
Executes the given tasks, returning a list of Futures holding
their status and results when all complete.
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 tasks |
|---|
| 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 |
Executes the given tasks, returning a list of Futures holding
their status and results
when all complete or the timeout expires, whichever happens first.
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 tasks |
|---|---|
| timeout | the maximum time to wait |
| unit | the time unit of the timeout argument |
| 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 |
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.
| tasks | the collection of tasks |
|---|---|
| timeout | the maximum time to wait |
| unit | the time unit of the timeout argument |
| 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 |
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.
| tasks | the collection of tasks |
|---|
| 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 |
Returns true if this executor has been shut down.
true if this executor has been shut down
Returns 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 down
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 awaitTermination
to do that.
Attempts 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 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 interrupt(), so any
task that fails to respond to interrupts may never terminate.
Submits a Runnable task for execution and returns a Future
representing that task. The Future's get method will
return the given result upon successful completion.
| task | the task to submit |
|---|---|
| result | the result to return |
| RejectedExecutionException | if the task cannot be scheduled for execution |
|---|---|
| NullPointerException | if the task is null |
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.
| task | the task to submit |
|---|
| RejectedExecutionException | if the task cannot be scheduled for execution |
|---|---|
| NullPointerException | if the task is null |
Submits a Runnable task for execution and returns a Future
representing that task. The Future's get method will
return null upon successful completion.
| task | the task to submit |
|---|
| RejectedExecutionException | if the task cannot be scheduled for execution |
|---|---|
| NullPointerException | if the task is null |