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FlexDoc/Javadoc 2.0 Demo Java Doc |
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 Executor.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.
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 ex) {
// (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().
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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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.
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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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boolean |
Returns true if this executor has been shut down.
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boolean |
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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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 value-returning task for execution and returns a
Future representing the pending results of the task.
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Future<?> |
Submits a Runnable task for execution and returns a Future
representing that task.
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Submits a Runnable task for execution and returns a Future
representing that task.
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Methods inherited from interface java.util.concurrent.Executor |
void shutdown |
() |
This method does not wait for previously submitted tasks to complete execution. Use awaitTermination to do that.
() |
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 Thread.interrupt(), so any task that fails to respond to interrupts may never terminate.
boolean isShutdown |
() |
boolean isTerminated |
() |
boolean awaitTermination |
(long timeout, TimeUnit unit) |
throws |
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.
Future<?> submit |
(Runnable task) |
throws |
throws |
throws |
throws |
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FlexDoc/Javadoc 2.0 Demo Java Doc |