public
interface
Executor
| java.util.concurrent.Executor |
 Known Indirect Subclasses
|
An object that executes submitted Runnable tasks. This
interface provides a way of decoupling task submission from the
mechanics of how each task will be run, including details of thread
use, scheduling, etc. An Executor is normally used
instead of explicitly creating threads. For example, rather than
invoking new Thread(new RunnableTask()).start() for each
of a set of tasks, you might use:
Developers
Executor executor = anExecutor();
executor.execute(new RunnableTask1());
executor.execute(new RunnableTask2());
...
However, the Executor interface does not strictly require
that execution be asynchronous. In the simplest case, an executor
can run the submitted task immediately in the caller's thread:
class DirectExecutor implements Executor {
public void execute(Runnable r) {
r.run();
}
}
More typically, tasks are executed in some thread other than the
caller's thread. The executor below spawns a new thread for each
task.
class ThreadPerTaskExecutor implements Executor {
public void execute(Runnable r) {
new Thread(r).start();
}
}
Many Executor implementations impose some sort of
limitation on how and when tasks are scheduled. The executor below
serializes the submission of tasks to a second executor,
illustrating a composite executor.
class SerialExecutor implements Executor {
final Queue<Runnable> tasks = new ArrayDeque<>();
final Executor executor;
Runnable active;
SerialExecutor(Executor executor) {
this.executor = executor;
}
public synchronized void execute(final Runnable r) {
tasks.add(new Runnable() {
public void run() {
try {
r.run();
} finally {
scheduleNext();
}
}
});
if (active == null) {
scheduleNext();
}
}
protected synchronized void scheduleNext() {
if ((active = tasks.poll()) != null) {
executor.execute(active);
}
}
}
The Executor implementations provided in this package
implement ExecutorService, which is a more extensive
interface. The ThreadPoolExecutor class provides an
extensible thread pool implementation. The Executors class
provides convenient factory methods for these Executors.
Memory consistency effects: Actions in a thread prior to
submitting a Runnable object to an Executor
happen-before
its execution begins, perhaps in another thread.
Public methods | |
|---|---|
abstract
void
|
execute(Runnable command)
Executes the given command at some time in the future. |
void execute (Runnable command)
Executes the given command at some time in the future. The command
may execute in a new thread, in a pooled thread, or in the calling
thread, at the discretion of the Executor implementation.
| Parameters | |
|---|---|
command |
Runnable:
the runnable task |
| Throws | |
|---|---|
RejectedExecutionException |
if this task cannot be accepted for execution |
NullPointerException |
if command is null |