`Subprocess.wait_for_exit` never resolves if process terminated before it is called about tornado HOT 3 OPEN

As long as Tornado is the only thing that touches the SIGCHLD handler, the child process is guaranteed to exist (in a zombie state) until os.waitpid (or another wait function) is called on it once. Could something else be installing a SIGCHLD handler, ignoring SIGCHLD, or calling os.wait directly? (In this example it seems wrong to use both p.proc.wait() and p.wait_for_exit() but if you've seen it in the wild I doubt it's that simple)

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Ok, interesting! As far as I understand, nothing else is happening. We were creating the subprocess (calling git init) and immediately called wait_for_exit on the following line.

However, we used the Subprocess class outside the tornado process (in a Celery worker instance). Could this have anything to do with it? We have now switched to Popen and wait, which works as intended. The docs don't mention anything about this.

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However, we used the Subprocess class outside the tornado process (in a Celery worker instance).

I'm confused (maybe because I've never used celery) - there's still a tornado IOLoop (or asyncio event loop) running in the worker process, right? If not you wouldn't be able to await p.wait_for_exit().

Celery does touch the SIGCLD handler although I'm not sure if it's possible for this to be run in a way that would clobber tornado's SIGCLD handler. It doesn't appear to call asyncio's set_child_watcher function but if something in the stack does, it could also cause this problem.

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