A delegating
ExecutorService with its own termination management.
VirtualExecutorService is used when you want to inject an
ExecutorService but you do not want to allow the explicit termination
of threads on shutdown request. It is particularly useful when the
ExecutorService to inject is shared by different components and
the life cycle of the components depend on the termination of the injected
ExecutorService.
ExecutorService globalExecutor = ...;
ExecutorService virtualExecutor = new VirtualExecutorService(globalExecutor);
ChannelFactory factory =
new NioServerSocketChannelFactory(virtualExecutor, virtualExecutor);
...
// ChannelFactory.releaseExternalResources() shuts down the executor and
// interrupts the I/O threads to terminate all I/O tasks and to release all
// resources acquired by ChannelFactory.
factory.releaseExternalResources();
// Note that globalExecutor is not shut down because VirtualExecutorService
// implements its own termination management. All threads which were acquired
// by ChannelFactory via VirtualExecutorService are returned to the pool.
assert !globalExecutor.isShutdown();
The differences from an ordinary ExecutorService
A shutdown request (
shutdown() or
shutdownNow()) does not
shut down its parent
Executor but simply sets its internal flag to
reject further execution request.
shutdownNow() interrupts only the thread which is executing the
task executed via VirtualExecutorService.
awaitTermination(long, TimeUnit) does not wait for real thread
termination but wait until VirtualExecutorService is shut down and
its active tasks are finished and the threads are returned to the parent
Executor.
