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ExecutorService pool = Executors.newFixedThreadPool(3);
Based on 84 examples
public interface ExecutorService extends Executor
An {@link Executor} that provides methods to manage termination and methods that can produce a {@link 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 {@link #shutdown} method will allow previously submitted tasks to execute before terminating, while the {@link #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 {@link Executor#execute} by creating and returning a {@link 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 {@link ExecutorCompletionService} can be used to write customized variants of these methods.)
The {@link 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()}.
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. |
List |
invokeAll(Collection tasks) Executes the given tasks, returning a list of Futures holding their status and results when all complete. |
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. |
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 |
Returns true if this executor has been shut down. |
boolean |
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 |
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 |
Submits a value-returning task for execution and returns a Future representing the pending results of the task. |
Future |
Submits a Runnable task for execution and returns a Future representing that task. |
Future |
Submits a Runnable task for execution and returns a Future representing that task. |
Methods inherited from class java.util.concurrent.Executor |
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execute |
Method Detail |
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public boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedException
timeout
- the maximum time to waitunit
- the time unit of the timeout argumentInterruptedException
- if interrupted while waitingpublic List invokeAll(Collection tasks) throws InterruptedException
tasks
- the collection of tasksInterruptedException
- if interrupted while waiting, in
which case unfinished tasks are cancelled.public List invokeAll(Collection tasks, long timeout, TimeUnit unit) throws InterruptedException
tasks
- 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 cancelledpublic Object invokeAny(Collection tasks) throws InterruptedException, ExecutionException
tasks
- the collection of tasksInterruptedException
- if interrupted while waitingExecutionException
- if no task successfully completespublic Object invokeAny(Collection tasks, long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException
tasks
- the collection of taskstimeout
- the maximum time to waitunit
- the time unit of the timeout argumentInterruptedException
- if interrupted while waitingExecutionException
- if no task successfully completesTimeoutException
- if the given timeout elapses before
any task successfully completespublic boolean isShutdown()
public boolean isTerminated()
public void shutdown()
public List shutdownNow()
There are no guarantees beyond best-effort attempts to stop processing actively executing tasks. For example, typical implementations will cancel via {@link Thread#interrupt}, so any task that fails to respond to interrupts may never terminate.
public Future submit(Callable task)
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 {@link Executors} class includes a set of methods that can convert some other common closure-like objects, for example, {@link java.security.PrivilegedAction} to {@link Callable} form so they can be submitted.
task
- the task to submitpublic Future submit(Runnable task)
task
- the task to submitpublic Future submit(Runnable task, Object result)
task
- the task to submitresult
- the result to return
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