Some pending events are preventing the Telemetry Data Server process to exit on its own

[nunoguedelha]

The process should exit automatically if there is no pending queued events in the Node Event Loop. But for some reason, there are pending events preventing the process to exit on its own. A workaround, consisting in calling process.exit() for forcing the exit, has been used so far, but here we try to identify the problem root cause and design a permanent proper solution accordingly.

References

Event Loop
https://nodejs.org/en/docs/guides/event-loop-timers-and-nexttick/#setimmediate-vs-settimeout
https://nodejs.dev/learn/the-nodejs-event-loop
https://nodejs.dev/learn/understanding-process-nexttick
https://developer.mozilla.org/en-US/docs/Web/JavaScript/EventLoop

• Closing all the ports manually (instead of letting the on exit callback do it). => does not solve the problem.
• Checking the pending handles and requests in the Event Loop. ⏳

[nunoguedelha]

Closing all the ports manually, and checking the pending handles and requests in the Event Loop ⌛

• Closing the ports
  2952072
• checking the pending handles and requests in the Event Loop
  nodejs/node#1128
  https://github.com/thlorenz/active-handles
  In the last promise handling...
  

  yarp-openmct/iCubTelemVizServer/terminationHandler.js

  Lines 22 to 29 in 2952072

  	Promise.all([subsetCpromise,subsetApromise.closeServers]).then(
  	function(values) {
  	values.forEach((v) => console.log(v));
  	// console.log(process._getActiveHandles());
  	console.log(process._getActiveRequests());
  	}
  	).catch(console.error);
  	}

  
  we use process._getActiveHandles() and process._getActiveRequests() to get the pending actions in the Event Loop.

Originally posted by @nunoguedelha in #61 (comment)