Maybe instead of releasing the lock in the forked child process, we should try to acquire the lock in the os.fork() implementation, and then release it?

Otherwise, suppose that a call to getaddrinfo (call #1) takes a long amount of time.  In the middle of it we fork, and then immediately try to call getaddrinfo (call #2, and call #1 is still happening) for some other address. At this point, since getaddrinfo isn't threadsafe, something bad will happen.