Release thread start barrier in case an error occurs

[andfoy]

Fixes #27

[ngoldbaum]

Can you add a test where a worker raises an unhandled exception (e.g. KeyboardInterrupt) and verify that it deadlocks before this PR and the test passes with this PR.

[ngoldbaum]

I think this is a rare case where a bare except or BaseException is the correct thing, since we probably do want to handle KeyboardInterrupt.

Rather than worrying about exactly which exceptions you want to handle, better to use a try/finally:

num_completed = 0
for worker in workers:
    try:
        worker.start()
        num_completed += 1
    finally:
        if num_completed < len(workers):
            barrier.abort()

[andfoy]

Can you add a test where a worker raises an unhandled exception

I think we cannot, since the instrumented code gets executed after the barrier has been put in place, we would need to somehow create the conditions under which threads cannot be spawned, something like

pytest-run-parallel/tests/test_run_parallel.py

Line 735 in 1de039e

monkeypatch.setattr("os.process_cpu_count", lambda: None, raising=False)

[ngoldbaum]

Ah you're right! Good point. Never mind.