Monotonic time on macOS 10.12+ should use mach_continuous_time()

[xsetech]

BPO	42107
Nosy	@ronaldoussoren, @vstinner, @ned-deily, @xSetech

^{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 = None
created_at = <Date 2020-10-21.10:37:25.123>
labels = ['OS-mac', 'type-bug', '3.10']
title = 'Monotonic time on macOS 10.12+ should use mach_continuous_time()'
updated_at = <Date 2020-10-21.18:55:54.519>
user = 'https://github.com/xsetech'

bugs.python.org fields:

activity = <Date 2020-10-21.18:55:54.519>
actor = 'ronaldoussoren'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['macOS']
creation = <Date 2020-10-21.10:37:25.123>
creator = 'sjunot'
dependencies = []
files = []
hgrepos = []
issue_num = 42107
keywords = []
message_count = 2.0
messages = ['379204', '379231']
nosy_count = 4.0
nosy_names = ['ronaldoussoren', 'vstinner', 'ned.deily', 'sjunot']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42107'
versions = ['Python 3.10']

Linked PRs

• gh-86273: On macOS >= 10.12, use clock_gettime(CLOCK_MONOTONIC_RAW) for time.monotonic #134521

[xsetech]

This blog post describes an issue with Apple's "CLOCK_UPTIME_RAW" where the clock is reset after a system that hibernates:

https://rachelbythebay.com/w/2020/10/20/ticktock/

According to Apple's documentation, CLOCK_UPTIME_RAW corresponds to mach_absolute_time():

https://developer.apple.com/documentation/kernel/1462446-mach_absolute_time

CPython is using mach_absolute_time() for its time.monotonic() implementation:

https://github.com/python/cpython/blob/f660567/Python/pytime.c#L7

time.monotonic() ought to be backed by the more appropriate mach_continuous_time() ("CLOCK_MONOTONIC_RAW"). Note it was introduced in macOS 10.12+:

https://developer.apple.com/documentation/kernel/1646199-mach_continuous_time

[ronaldoussoren]

See also bpo-41303, which discusses using mach_continuous_time in another context.

If using a different clock is necessary I'd prefer to use clock_gettime(CLOCK_MONOTONIC_RAW) instead of mach_continuous_time(), as the former is a more cross-platform API.

BTW. Please hold off from merging a patch for this until the macOS 11 support code in bpo-41100 is in, this is bound to cause a merge conflict otherwise.