Using Asynchronous timeouts in the Java WebSocket API

Sending messages in an asynchronous manner avoid blocking the sending thread. This is a great where your solution needs to scale in order to support a large number of clients.

But there is a limit on how long can we wait for the asynchronous process to complete

The Java WebSocket API gives you a few options in this regard

Async Timeout support

• first and foremost, there is a notion of a timeout and this can be configured using the setSendTimeout method in the RemoteEndpoint.Async interface
• secondly, the failure result manifests itself using the Future object or java.websocket.SendResult

How do timeouts manifest ?

It depends on which strategy you’re using in order to send your messages

• Callback based
• Future (java.util.concurrent) based

In case you are using the java.websocket.SendHandler i.e. the callback handler route, the timeout exception details will be available via SendResult.getException()

	….
	public void broadcast(Session s, String msg){
	RemoteEndpoint asyncHandle = s.getRemoteAsync();
	asyncHandle.setSendTimeout(1000); //1 second
	asyncHandle.sendText(msg,
	new SendHandler(){
	@Override
	public void onResult(SendResult result) {
	if(!result.isOK()){
	System.out.println("Async send failure: "+ result.getException());
	}
	}
	}); //will timeout after 2 seconds
	tracker.get(); //will throw java.util.ExecutionException if the process had timed out
	}
	….

view raw

WebSocketTimeout_SendHandler.txt

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If you chose to use the Future to track the completion, calling it get method will result in a java.util.concurrent.ExecutionException

	….
	public void broadcast(Session s, String msg){
	RemoteEndpoint asyncHandle = s.getRemoteAsync();
	asyncHandle.setSendTimeout(2000); //2000 ms
	Future<Void> tracker = asyncHandle.sendText(msg); //will timeout after 2 seconds
	tracker.get(); //will throw java.util.ExecutionException if the process had timed out
	}
	….

view raw

WebSocketTimeout_Future.txt

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Further reading

• eBook – Java WebSocket API Handbook
• Java WebSocket API specification
• Other WebSocket blogs

Cheers!