https://github.com/python/cpython/commit/4b97c724e0715af049b2c0b226b4988e1f3... commit: 4b97c724e0715af049b2c0b226b4988e1f30df70 branch: 3.11 author: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> committer: vstinner <vstinner@python.org> date: 2023-09-29T15:25:34+02:00 summary: [3.11] gh-109955 : Update state transition comments for asyncio.Task (GH-109910) (#109993) gh-109955 : Update state transition comments for asyncio.Task (GH-109910) (cherry picked from commit 45cf5b0c69bb5c51f33fc681d90c45147e311ddf) Co-authored-by: Kristján Valur Jónsson <sweskman@gmail.com> Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com> files: M Lib/asyncio/tasks.py diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py index 3e07ce5294c8d..6ca545e30acd9 100644 --- a/Lib/asyncio/tasks.py +++ b/Lib/asyncio/tasks.py @@ -81,15 +81,25 @@ class Task(futures._PyFuture): # Inherit Python Task implementation """A coroutine wrapped in a Future.""" # An important invariant maintained while a Task not done: + # _fut_waiter is either None or a Future. The Future + # can be either done() or not done(). + # The task can be in any of 3 states: # - # - Either _fut_waiter is None, and _step() is scheduled; - # - or _fut_waiter is some Future, and _step() is *not* scheduled. + # - 1: _fut_waiter is not None and not _fut_waiter.done(): + # __step() is *not* scheduled and the Task is waiting for _fut_waiter. + # - 2: (_fut_waiter is None or _fut_waiter.done()) and __step() is scheduled: + # the Task is waiting for __step() to be executed. + # - 3: _fut_waiter is None and __step() is *not* scheduled: + # the Task is currently executing (in __step()). # - # The only transition from the latter to the former is through - # _wakeup(). When _fut_waiter is not None, one of its callbacks - # must be _wakeup(). - - # If False, don't log a message if the task is destroyed whereas its + # * In state 1, one of the callbacks of __fut_waiter must be __wakeup(). + # * The transition from 1 to 2 happens when _fut_waiter becomes done(), + # as it schedules __wakeup() to be called (which calls __step() so + # we way that __step() is scheduled). + # * It transitions from 2 to 3 when __step() is executed, and it clears + # _fut_waiter to None. + + # If False, don't log a message if the task is destroyed while its # status is still pending _log_destroy_pending = True