Last time I had to make a major change related to signal handling, it was in the asyncio module because of a race conditon which occurred on FreeBSD.commitfe5649c7b7bf52147480d6b1124a3d8e3597aee3Author: Victor Stinner <victor.stinner@gmail.com>Date:   Thu Jul 17 22:43:40 2014 +0200    Python issue#21645, Tulip issue 192: Rewrite signal handling        Since Python 3.3, the C signal handler writes the signal number into the wakeup    file descriptor and then schedules the Python call using Py_AddPendingCall().        asyncio uses the wakeup file descriptor to wake up the event loop, and relies    on Py_AddPendingCall() to schedule the final callback with call_soon().        If the C signal handler is called in a thread different than the thread of the    event loop, the loop is awaken but Py_AddPendingCall() was not called yet. In    this case, the event loop has nothing to do and go to sleep again.    Py_AddPendingCall() is called while the event loop is sleeping again and so the    final callback is not scheduled immediatly.        This patch changes how asyncio handles signals. Instead of relying on    Py_AddPendingCall() and the wakeup file descriptor, asyncio now only relies on    the wakeup file descriptor. asyncio reads signal numbers from the wakeup file    descriptor to call its signal handler.