edu.emory.mathcs.backport.java.util.concurrent
public interface ExecutorService extends Executor
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 ExecutorService method will allow previously submitted tasks to execute before terminating, while the ExecutorService 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 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.
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 {@code Runnable} or {@code Callable} task to an {@code ExecutorService} happen-before any actions taken by that task, which in turn happen-before the result is retrieved via {@code Future.get()}.
Since: 1.5
Method Summary | |
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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.
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List | invokeAll(Collection tasks)
Executes the given tasks, returning a list of Futures holding
their status and results when all complete.
Future is true for each
element of the returned list.
|
List | invokeAll(Collection 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.
Future is true for each
element of the returned list.
|
Object | invokeAny(Collection tasks)
Executes the given tasks, returning the result
of one that has completed successfully (i.e., without throwing
an exception), if any do. |
Object | invokeAny(Collection 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.
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void | shutdown()
Initiates an orderly shutdown in which previously submitted
tasks are executed, but no new tasks will be accepted.
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List | 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.
|
Future | submit(Callable task)
Submits a value-returning task for execution and returns a
Future representing the pending results of the task. |
Future | submit(Runnable task, Object result)
Submits a Runnable task for execution and returns a Future
representing that task. |
Future | submit(Runnable task)
Submits a Runnable task for execution and returns a Future
representing that task. |
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
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
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
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 of its elements are null IllegalArgumentException if tasks is empty ExecutionException if no task successfully completes RejectedExecutionException if tasks cannot be scheduled for execution
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, 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
Returns: true if this executor has been shut down
Returns: true if all tasks have completed following 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 java.lang.RuntimePermission("modifyThread"), or the security manager's checkAccess method denies access.
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
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 java.lang.RuntimePermission("modifyThread"), or the security manager's checkAccess method denies access.
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, java.security.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
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
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