Wait, I think there's a misunderstanding here.
POSIX does indeed leave undefined the behavior of syscalls when a
signal is received: whether or not it fails with EINTR depends on the
operating system, the SA_RESTART flag, etc.

But the tests we're talking about send signals whose default actions
are to terminate the process (e.g. SIGTERM, SIGHUP, etc): I cannot
beleive AIX doesn't terminate the processes in these situations, I
think it's a bug in asyncio which prevent the termination from being
detected (David, you can just use "ps" to check that the processes are
indeed terminated).