sched cancel (wrong item removed from queue) #79124

ajneu · 2018-10-09T12:28:53Z

BPO	34943
Superseder	bpo-19270: sched.cancel() doesn't distinguish equal events and can break order

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2021-11-22.10:40:14.610>
created_at = <Date 2018-10-09.12:28:53.449>
labels = ['3.7', 'type-bug', 'library']
title = 'sched cancel (wrong item removed from queue)'
updated_at = <Date 2021-11-22.10:40:14.610>
user = 'https://bugs.python.org/ajneu'

bugs.python.org fields:

activity = <Date 2021-11-22.10:40:14.610>
actor = 'iritkatriel'
assignee = 'none'
closed = True
closed_date = <Date 2021-11-22.10:40:14.610>
closer = 'iritkatriel'
components = ['Library (Lib)']
creation = <Date 2018-10-09.12:28:53.449>
creator = 'ajneu'
dependencies = []
files = []
hgrepos = []
issue_num = 34943
keywords = []
message_count = 2.0
messages = ['327396', '327397']
nosy_count = 1.0
nosy_names = ['ajneu']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '19270'
type = 'behavior'
url = 'https://bugs.python.org/issue34943'
versions = ['Python 3.6', 'Python 3.7']

ajneu · 2018-10-09T12:28:53Z

Hi,

in the code given below, the last assert fails
when running with
/mingw64/bin/python3 (Python 3.7.0 -- mingw64's python3 from msys2 project)
C:\Python36\python.exe (Python 3.6.6 -- windows installer)

It does not fail when running with
/usr/bin/python3 (Python 3.6.6 -- msys's python3 from msys2 project)

import sched, time, threading

class A(threading.Thread):
    def __init__(self, sched):
        threading.Thread.__init__(self)
        self._sched = sched
        self.start()

    def run(self):
        self._sched.run()




s = sched.scheduler(time.monotonic, time.sleep)

ev1=None
def go1(a=''):
    print(a)
    global ev1
    ev1 = s.enterabs(time.monotonic()+1, 1, go1, argument=('a',))

ev2=None 
def go2(a=''):
    print(a)
    global ev2
    ev2 = s.enterabs(time.monotonic()+1, 1, go2, argument=('b',))


ev1 = s.enterabs(time.monotonic()+1, 1, go1, argument=('a',))
ev2 = s.enterabs(time.monotonic()+1, 1, go2, argument=('b',))
a = A(s)
time.sleep(2.5)
print('schedu queue before', s.queue)
assert 1 == 1
print('remove', ev2)
assert ev2 in s.queue
s.cancel(ev2)
print('schedu queue after', s.queue)
assert ev2 not in s.queue   # fails (SOMETIMES)

# what is going on here???
# does the last assert also fail from anybody else?

ajneu · 2018-10-09T12:46:30Z

Ah ...
https://bugs.python.org/issue19270 amazing!

assert ev1 == ev2
does not fail! (the equality just checks timestamp as far as I can see)

Terrible. In particular: Terrible if the documentation blatently lies to me: https://docs.python.org/3/library/sched.html#sched.scheduler.cancel

ajneu mannequin added 3.7 (EOL) end of life stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error labels Oct 9, 2018

iritkatriel closed this as completed Nov 22, 2021

ezio-melotti transferred this issue from another repository Apr 10, 2022

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sched cancel (wrong item removed from queue) #79124

sched cancel (wrong item removed from queue) #79124

ajneu mannequin commented Oct 9, 2018

ajneu mannequin commented Oct 9, 2018

ajneu mannequin commented Oct 9, 2018

sched cancel (wrong item removed from queue) #79124

sched cancel (wrong item removed from queue) #79124

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ajneu mannequin commented Oct 9, 2018

ajneu mannequin commented Oct 9, 2018

ajneu mannequin commented Oct 9, 2018