java.util.concurrent.ExecutorService
java.util.concurrent.ExecutorService |
Executor
|
An Executor that provides methods to manage termination and
methods that can produce a 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 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.
Usage Example
Here is a sketch of a network service in which threads in a thread
pool service incoming requests. It uses the preconfigured
newFixedThreadPool(int) 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
}
}
Known Indirect Subclasses
Summary
Details
Public Methods
public
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.
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
Executes the given tasks, returning their results
when all complete or the timeout expires, whichever happens first.
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.
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 thiese tasks will
not have completed.
Executes the given tasks, returning their results
when all complete.
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.
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.
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.
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.
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.
Parameters
tasks
| the collection of tasks |
Returns
- The result returned by one of the tasks.
public
boolean
isShutdown()
Returns
true if this executor has been shut down.
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.
Returns
- true if all tasks have completed following shut down
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.
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
RuntimePermission("modifyThread"),
or the security manager's checkAccess method denies access.
|
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 interrupt(), so if any
tasks mask or fail to respond to interrupts, they 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
RuntimePermission("modifyThread"),
or the security manager's checkAccess method denies access.
|
Submits a Runnable task for execution and returns a Future
representing that task.
Returns
- a Future representing pending completion of the task,
and whose get() method will return null
upon completion.
public
Future<T>
submit(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.
Parameters
task
| the task to submit |
result
| the result to return |
Returns
- a Future representing pending completion of the task,
and whose get() method will return the given result
upon completion.
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 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.
Returns
- a Future representing pending completion of the task