Long running process exits with IOSelectorsException

[PMunch]

I have a program which runs for a long time, every once in a time sending something over MQTT. Recently I got a crash with this error message:

  /home/peter/.choosenim/toolchains/nim-2.0.0/lib/pure/asyncdispatch.nim(2022) waitFor
  /home/peter/.choosenim/toolchains/nim-2.0.0/lib/pure/asyncdispatch.nim(1711) poll
  /home/peter/.choosenim/toolchains/nim-2.0.0/lib/pure/asyncdispatch.nim(1452) runOnce
  /home/peter/.choosenim/toolchains/nim-2.0.0/lib/pure/asyncdispatch.nim(269) processPendingCallbacks
  /home/peter/.nimble/pkgs2/nmqtt-1.0.5-e9b66114ab9f39559f01e200164bfff921c0c8f3/nmqtt.nim(1094) runConnect (Async)
  /home/peter/.nimble/pkgs2/nmqtt-1.0.5-e9b66114ab9f39559f01e200164bfff921c0c8f3/nmqtt.nim(1066) connectBroker (Async)
  /home/peter/.choosenim/toolchains/nim-2.0.0/lib/pure/asyncnet.nim(296) dial (Async)
  /home/peter/.choosenim/toolchains/nim-2.0.0/lib/pure/asyncdispatch.nim(1902) dial
  /home/peter/.choosenim/toolchains/nim-2.0.0/lib/pure/asyncdispatch.nim(1868) tryNextAddrInfo
  /home/peter/.choosenim/toolchains/nim-2.0.0/lib/pure/asyncdispatch.nim(1733) createAsyncNativeSocket
  /home/peter/.choosenim/toolchains/nim-2.0.0/lib/pure/asyncdispatch.nim(1247) register
  /home/peter/.choosenim/toolchains/nim-2.0.0/lib/pure/ioselects/ioselectors_epoll.nim(136) registerHandle
  /home/peter/.choosenim/toolchains/nim-2.0.0/lib/pure/selectors.nim(287) raiseIOSelectorsError
Exception message: Maximum number of descriptors is exhausted!
 [IOSelectorsException]

Might be something else in my program which leaks descriptors, but figured I'd report it here first since the error was triggered in nmqtt. The MqttContext lives for the lifetime of the program, and the messages are sent wrapped in a start/disconnect construct (but not in a try/finally one).

[python36]

Hi @PMunch , thanks for reporting this!
This looks like a potential descriptor leak. If a connection attempt fails and the socket isn't properly closed (especially without try/finally), descriptors can indeed accumulate over time.
To help me investigate:

1. Is this issue still relevant/reproducible for you on the latest version?
2. Could you provide a minimal code snippet or the part of your program where you handle the start/disconnect logic?

Seeing how you manage the MqttContext and handle potential connection errors would be very helpful to determine if the leak is inside nmqtt or in the user-level implementation. Thanks!