ExecutorServicepublic interface ExecutorService implements 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 stop accepting new tasks. After being shut down, the executor
will eventually terminate, at which point no tasks are actively
executing, no tasks are awaiting execution, and no new tasks can be
submitted.
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.
Usage Example
Here is a sketch of a network service in which threads in a thread
pool service incoming requests. It uses the preconfigured {@link
Executors#newFixedThreadPool} factory method:
class NetworkService {
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 serve() {
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
}
}
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| Methods Summary |
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| public boolean | awaitTermination(long timeout, java.util.concurrent.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.
| | public java.util.List | invokeAll(java.util.Collection tasks, long timeout, java.util.concurrent.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.
{@link Future#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.
| | public java.util.List | invokeAll(java.util.Collection tasks)Executes the given tasks, returning a list of Futures holding
their status and results when all complete.
{@link Future#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.
| | public T | invokeAny(java.util.Collection tasks)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.
| | public T | invokeAny(java.util.Collection tasks, long timeout, java.util.concurrent.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.
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.
| | public boolean | isShutdown()Returns true if this executor has been shut down.
| | public boolean | isTerminated()Returns true if all tasks have completed following shut down.
Note that isTerminated is never true unless
either shutdown or shutdownNow was called first.
| | public void | shutdown()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.
| | public java.util.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.
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 if any
tasks mask or fail to respond to interrupts, they may never terminate.
| | public java.util.concurrent.Future | submit(java.util.concurrent.Callable task)Submits a value-returning task for execution and returns a Future
representing the pending results of the 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.
| | public java.util.concurrent.Future | submit(java.lang.Runnable task, T result)Submits a Runnable task for execution and returns a Future
representing that task that will upon completion return
the given result
| | public java.util.concurrent.Future | submit(java.lang.Runnable task)Submits a Runnable task for execution and returns a Future
representing that task.
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