bpo-38323, asyncio: Fix MultiLoopChildWatcher race condition by vstinner · Pull Request #26536 · python/cpython

Fix a race condition in asyncio MultiLoopChildWatcher: call the loop
add_signal_handler() rather than calling directly signal.signal(), so
signal.set_wakeup_fd() is used to wake up the event loop when the
SIGCHLD signal is received. Previously, the event loop could block
forever if the signal was received while the loop was idle. The
signal was only proceed when another event woke up the event loop.