Ludwig isn't really proposing that subprocess.Popen be thread-safe. That
would imply that you could mess with the same Popen instance
concurrently from separate threads, which shouldn't be allowed. But
instead, he's asking that it not be thread-hostile: that the constructor
can be called from multiple threads. Since every call in a threaded app
would need to be protected by the same lock, and there's no good place
to put that lock, it's a reasonable request. Most existing python types
provide this guarantee too: list() can be called concurrently from lots
of threads. So I think it's a real bug.