public interfaceExecutorServiceextendsExecutor
Executor that provides methods to manage termination and methods that can produce aFuture for tracking progress of one or more asynchronous tasks.AnExecutorService can be shut down, which will cause it to reject new tasks. Two different methods are provided for shutting down anExecutorService. Theshutdown() method will allow previously submitted tasks to execute before terminating, while theshutdownNow() 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 unusedExecutorService should be shut down to allow reclamation of its resources.
Methodsubmit extends base methodExecutor.execute(Runnable) by creating and returning aFuture that can be used to cancel execution and/or wait for completion. MethodsinvokeAny andinvokeAll 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. (ClassExecutorCompletionService can be used to write customized variants of these methods.)
TheExecutors 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 } }ExecutorService in two phases, first by callingshutdown to reject incoming tasks, and then callingshutdownNow, 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 aRunnable orCallable task to anExecutorServicehappen-before any actions taken by that task, which in turnhappen-before the result is retrieved viaFuture.get().
| Modifier and Type | Method | 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<? extendsCallable<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<? extendsCallable<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<? extendsCallable<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<? extendsCallable<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. UseawaitTermination 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 holdRuntimePermission("modifyThread"), or the security manager'scheckAccess method denies access.List<Runnable> shutdownNow()
This method does not wait for actively executing tasks to terminate. UseawaitTermination to do that.
There are no guarantees beyond best-effort attempts to stop processing actively executing tasks. For example, typical implementations will cancel viaThread.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 holdRuntimePermission("modifyThread"), or the security manager'scheckAccess 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 thatisTerminated is nevertrue unless eithershutdown orshutdownNow was called first.true if all tasks have completed following shut downboolean awaitTermination(long timeout,TimeUnit unit) throwsInterruptedException
timeout - the maximum time to waitunit - the time unit of the timeout argumenttrue if this executor terminated andfalse 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 formresult = exec.submit(aCallable).get();
Note: TheExecutors class includes a set of methods that can convert some other common closure-like objects, for example,PrivilegedAction toCallable 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 returnnull uponsuccessful 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<? extendsCallable<T>> tasks) throwsInterruptedException
Future.isDone() istrue for each element of the returned list. Note that acompleted 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 arenullRejectedExecutionException - if any task cannot be scheduled for execution<T> List<Future<T>> invokeAll(Collection<? extendsCallable<T>> tasks, long timeout,TimeUnit unit) throwsInterruptedException
Future.isDone() istrue for each element of the returned list. Upon return, tasks that have not completed are cancelled. Note that acompleted 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 arenullRejectedExecutionException - if any task cannot be scheduled for execution<T> T invokeAny(Collection<? extendsCallable<T>> tasks) throwsInterruptedException,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 isnullIllegalArgumentException - if tasks is emptyExecutionException - if no task successfully completesRejectedExecutionException - if tasks cannot be scheduled for execution<T> T invokeAny(Collection<? extendsCallable<T>> tasks, long timeout,TimeUnit unit) throwsInterruptedException,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 isnullTimeoutException - if the given timeout elapses before any task successfully completesExecutionException - if no task successfully completesRejectedExecutionException - if tasks cannot be scheduled for execution