Asyncio watcher 'MultiLoopChildWatcher' currently doesn't work well on Solaris and can freeze the event loop indefinitely. This was reported upstream: https://bugs.python.org/issue37573 diff -wpruN --no-dereference '--exclude=*.orig' a~/Lib/asyncio/unix_events.py a/Lib/asyncio/unix_events.py --- a~/Lib/asyncio/unix_events.py 1970-01-01 00:00:00 +++ a/Lib/asyncio/unix_events.py 1970-01-01 00:00:00 @@ -30,7 +30,7 @@ __all__ = ( 'SelectorEventLoop', 'AbstractChildWatcher', 'SafeChildWatcher', 'FastChildWatcher', 'PidfdChildWatcher', - 'MultiLoopChildWatcher', 'ThreadedChildWatcher', + 'ThreadedChildWatcher', 'DefaultEventLoopPolicy', 'EventLoop', )