Sending to WebSocket from multiple threads crashes Jetty. Maybe synchronize?

Actual behavior (the bug) When I call .send on a WsSession from multiple threads, I receive the following:

java.lang.IllegalStateException: Blocking message pending 10000 for BLOCKING
	at org.eclipse.jetty.websocket.common.WebSocketRemoteEndpoint.lockMsg(WebSocketRemoteEndpoint.java:130)
	at org.eclipse.jetty.websocket.common.WebSocketRemoteEndpoint.sendString(WebSocketRemoteEndpoint.java:386)
	at io.javalin.websocket.WsSession.send(WsSession.kt:24)
	at ch.hsr.dsl.dwrtc.websocket.WebSocketHandler.onReceiveMessageFromSignaling(WebsocketHandler.kt:117)

Our code calling this (line 117) (slightly modified): session.send("XYZ")

Expected behavior WsSession.send() blocks/is synchronized, and message is sent slightly later without a crash

To Reproduce This is a bit hard… I can come up with a little example if you want, but I don’t have the time now (I’ll be back in a few hours). Just assume that our code is called from multiple threads.

Additional context Only happens when WsSession.send() is called from multiple threads.

My solution is to make my code @Synchronized. I suggest synchronizing WsSession.send. But, if you want to leave that over to users, that’s fine for me too 😃

[tipsy]

Thanks @lroellin. I don’t really mind adding a @Synchronized annotation, but I was hoping Jetty would have taken care of this. I added an input wanted label, hopefully a Jetty/Java threading pro can chime in.

[lroellin]

Ok, I tried it using session.remote.sendString since it is kind-of fire-and-forget. However, I’m still hitting the error “java.lang.IllegalStateException: Blocking message pending 10000 for BLOCKING”

Then I tried session.remote.sendStringByFuture but did not check the future. I still sometimes get errors, but I unfortunately dropped the log…

I think we can close this issue for now. I’ll see if the Jetty methods help me, and if not I’ll synchronize myself. Could also be that I’m having trouble in my code that is not related to Javalin 😉

Thx for your help!