Author vstinner
Recipients njs, vstinner
Date 2017-04-11.10:20:12
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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.

commit fe5649c7b7bf52147480d6b1124a3d8e3597aee3
Author: Victor Stinner <>
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.
Date User Action Args
2017-04-11 10:20:13vstinnersetrecipients: + vstinner, njs
2017-04-11 10:20:13vstinnersetmessageid: <>
2017-04-11 10:20:13vstinnerlinkissue30038 messages
2017-04-11 10:20:12vstinnercreate