[Python-checkins] [python/cpython] 0b7629: bpo-30038: fix race condition in signal delivery +...

[GitHub]

  Branch: refs/heads/3.6
  Home:   https://github.com/python/cpython
  Commit: 0b7629cd846e3e160ac07cafc4e97644024f11b8
      https://github.com/python/cpython/commit/0b7629cd846e3e160ac07cafc4e97644024f11b8
  Author: Victor Stinner <victor.stinner at gmail.com>
  Date:   2017-06-10 (Sat, 10 Jun 2017)

  Changed paths:
    M Modules/signalmodule.c

  Log Message:
  -----------
  bpo-30038: fix race condition in signal delivery + wakeup fd (#1082) (#2075)

Before, it was possible to get the following sequence of
events (especially on Windows, where the C-level signal handler for
SIGINT is run in a separate thread):

- SIGINT arrives
- trip_signal is called
- trip_signal writes to the wakeup fd
- the main thread wakes up from select()-or-equivalent
- the main thread checks for pending signals, but doesn't see any
- the main thread drains the wakeup fd
- the main thread goes back to sleep
- trip_signal sets is_tripped=1 and calls Py_AddPendingCall to notify
  the main thread the it should run the Python-level signal handler
- the main thread doesn't notice because it's asleep

This has been causing repeated failures in the Trio test suite:
  https://github.com/python-trio/trio/issues/119
(cherry picked from commit 4ae01496971624c75080431806ed1c08e00f22c7)