The websockets guide here.... https://ci.inria.fr/pharo-contribution/job/EnterprisePharoBook/ lastSuccessfulBuild/artifact/book-result/WebSockets/WebSockets.html says "Reading and sending are completely separate and independent" and the class comment says its "full-duplex". From these I presume sending and receiving are okay to occur in separate threads, but this is not explicitly stated, so can someone confirm this? So for the given example.... | webSocket | webSocket := ZnWebSocket to: 'ws://echo.websocket.org'. [ webSocket sendMessage: 'Pharo Smalltalk using Zinc WebSockets !'; readMessage ] ensure: [ webSocket close ]. re-implementing as follows seems to work... webSocket := ZnWebSocket to: 'ws://echo.websocket.org'. [ webSocket runWith: [ :msg | Transcript crShow: msg ] ] forkAt: 35. webSocket sendMessage: 'Pharo Smalltalk using Zinc WebSockets !'. webSocket sendMessage: 'Another multi-thread echo'. webSocket close but that could just be by luck, so I ask. btw, if I don't send the #close in the last line, after ~30 seconds I get an error ConnectionClosed: Cannot write data which seems reasonable that the other end timed out and closed the connection, but when I send the #close, after ~30 seconds I get an error... PrimitiveFailed: primitive #primSocketReceiveDataAvailable: in Socket failed which is unfriendly. What is the best way to neatly stop trying to receive data when we explicitly close the websocket? cheers -ben P.S. I wonder if when a ZnWebSocket is closed, it might be worthwhile to do "role:=#closed" to provide some visibility of its state in its GTInspector [Raw] tab..