cmd() blocks when other thread blocks on get_packets()

[martinerikwerner-aac]

Copy of behaviour-presumed-issue from BallAerospace/COSMOS#1786 which also exists in OpenC3.

When combining get_packets() and cmd() calls in a multi-threaded script, cmd() unexpectedly(?) seems to block while get_packets() is blocking.

I would expect that cmd() called from a separate thread should proceed without blocking regardless of any calls to get_packets()?

I have adapted the reproducing plugin and reproduced the issue with OpenC3.

To Reproduce

1. Install the plugin from https://github.com/martinerikwerner-aac/openc3-plugin-cmd-blocking
2. Start the loopback.rb script via script runner
3. Connect the TEST interface
4. Start the test.rb script via script runner
5. Observe the log output

Expected behavior

The log output should show regular and frequent timestamps from both the "producer" and the "consumer", and in particular it should not raise a timeout exception.

Environment

• OS: Debian 11
• OpenC3 Version 5.0.11
• Browser
  -- [x] Mozilla Firefox

[ryanmelt]

There are a couple things going on here.

1. I'm going to update the blocking functionality of get_packets to be implemented client side instead of server side. That will prevent locking up the API across threads.
2. There are other cases where you might run into a similar scenario. The underlying JsonDRbObject class in the api is built mutex protected so you can only have one API request at a time. The workaround for that is to create another JsonDRbObject in your other thread which will be able to make requests in parallel with a new connection to the API.

[ryanmelt]

will be closed by #188