Package org.agrona.concurrent

Class ShutdownSignalBarrier

java.lang.Object

org.agrona.concurrent.ShutdownSignalBarrier

All Implemented Interfaces:

AutoCloseable

public final class ShutdownSignalBarrier
extends Object
implements AutoCloseable

One time witness for blocking one or more threads until:

• Thread blocked in await() is interrupted.
• JVM shutdown sequence begins (see Runtime.addShutdownHook(Thread)).
• signal() or signalAll() is invoked programmatically.

Useful for shutting down a service.

Note: ShutdownSignalBarrier must be closed last to ensure complete service(s) termination and to allow JVM to exit. Not calling close() method might result in JVM hanging indefinitely.

Here is an example on how to use this API to await service termination.

 
 class UsageSample
 {
   public static void main(final String[] args)
   {
     try (ShutdownSignalBarrier barrier = new ShutdownSignalBarrier();
         MyService service = new MyService())
     {
          barrier.await();
     }
   }
 }

 class MyService implements AutoCloseable
 {
     ...
 }
 

It is also possible to use barrier to implement a flag that is checked in the main thread.

 
 class FlagSample
 {
   public static void main(final String[] args)
   {
     final AtomicBoolean running = new AtomicBoolean(true);
     try (ShutdownSignalBarrier barrier = new ShutdownSignalBarrier(() -> running.set(false))
     {
          while (running.get())
          {
              ...
          }
     }
   }
 }
 

See Also:

• Runtime.addShutdownHook(Thread)

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	ShutdownSignalBarrier.SignalHandler	Interface for notification when is signaled.

Constructor Summary

Constructors

Constructor	Description
ShutdownSignalBarrier()	Construct and register the witness ready for use.
ShutdownSignalBarrier(ShutdownSignalBarrier.SignalHandler signalHandler)	Construct and register the witness ready for use with a signal handler.

Method Summary

Modifier and Type	Method	Description
void	await()	Await the reception of the shutdown signal.
void	close()	Close this ShutdownSignalBarrier to allow JVM termination.
void	remove()	Remove the witness from the shutdown signals.
void	signal()	Programmatically signal awaiting thread on the latch associated with this witness.
void	signalAll()	Programmatically signal all awaiting threads.
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Details

ShutdownSignalBarrier

public ShutdownSignalBarrier()

Construct and register the witness ready for use.

ShutdownSignalBarrier

public ShutdownSignalBarrier(ShutdownSignalBarrier.SignalHandler signalHandler)

Construct and register the witness ready for use with a signal handler.

Parameters:

signalHandler - to notify.

Throws:

NullPointerException - if null == signalHandler.

Method Details

signal

public void signal()

Programmatically signal awaiting thread on the latch associated with this witness.

signalAll

public void signalAll()

Programmatically signal all awaiting threads.

remove

public void remove()

Remove the witness from the shutdown signals.

await

public void await()

Await the reception of the shutdown signal.

close

public void close()

Close this ShutdownSignalBarrier to allow JVM termination.

Specified by:

close in interface AutoCloseable

toString

public String toString()

Overrides:

toString in class Object