Difference between revisions of "Oslo/blueprints/time monotonic"
< Oslo
(Created page with "== Authors == * Victor Stinner - victor.stinner@enovance.com == Rationale == Using time.time() to compute timeouts is wrong. The elapsed time may be wrong on update of the...") |
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| Line 11: | Line 11: | ||
== Use time.monotonic() == | == Use time.monotonic() == | ||
| − | Eventlet should use time_monotonic() instead of time.time(). Example of bug of time.time(): | + | Eventlet should use time_monotonic() instead of time.time(). Example of bug of time.time(): [https://www.mail-archive.com/openstack-dev@lists.openstack.org/msg18658.html|openstack-dev: time.sleep is affected by eventlet.monkey_patch()]. |
| − | https://www.mail-archive.com/openstack-dev@lists.openstack.org/ | ||
For greenlet, the monotonic clock can be used with something like that: | For greenlet, the monotonic clock can be used with something like that: | ||
| Line 18: | Line 17: | ||
eventlet.hubs._threadlocal.hub = eventlet.hubs.get_default_hub().Hub(monotonic_time) | eventlet.hubs._threadlocal.hub = eventlet.hubs.get_default_hub().Hub(monotonic_time) | ||
| − | time_monotonic() should be used for any function computing a timeout. Recent example: | + | time_monotonic() should be used for any function computing a timeout. Recent example: [https://review.openstack.org/#/c/71003/|oslo.messaging: Add an optional timeout parameter to Listener.poll] |
| − | https://review.openstack.org/#/c/71003/ | ||
== Implementation == | == Implementation == | ||
| − | The following patch is based on the file time_monotonic.py from my Trollius project. Trollius is tested on Linux, Mac OS X, Windows, FreeBSD and OpenIndiana (which is almost Solaris): | + | The following patch is based on the file time_monotonic.py from my Trollius project. Trollius is tested on Linux, Mac OS X, Windows, FreeBSD and OpenIndiana (which is almost Solaris): [https://review.openstack.org/#/c/85717/|timeutils: add time_monotonic() function]. The reimplement reuses time.monotonic() if available. |
| − | https://review.openstack.org/#/c/85717/ | ||
== Alternatives == | == Alternatives == | ||
| Line 31: | Line 28: | ||
** On Linux, it uses CLOCK_MONOTONIC_RAW which is wrong according to my PEP 418. Extract: "Slewing is generally desirable (i.e. we should use CLOCK_MONOTONIC, not CLOCK_MONOTONIC_RAW) if one wishes to measure "real" time (and not a time-like object like CPU cycles)." | ** On Linux, it uses CLOCK_MONOTONIC_RAW which is wrong according to my PEP 418. Extract: "Slewing is generally desirable (i.e. we should use CLOCK_MONOTONIC, not CLOCK_MONOTONIC_RAW) if one wishes to measure "real" time (and not a time-like object like CPU cycles)." | ||
** Monotime module doesn't support Windows nor Solaris. Does it matters for Oslo Incubator? | ** Monotime module doesn't support Windows nor Solaris. Does it matters for Oslo Incubator? | ||
| − | + | ** It doesn't reuse time.monotonic() if available. | |
| − | + | * python-monotonic-time | |
| + | ** It doesn't look to be available on PyPI: https://github.com/gavinbeatty/python-monotonic-time | ||
Revision as of 14:47, 7 April 2014
Authors
- Victor Stinner - victor.stinner@enovance.com
Rationale
Using time.time() to compute timeouts is wrong. The elapsed time may be wrong on update of the system clock. A monotonic clock should be used to avoid this issue.
For a longer rationale, read the 418.
Use time.monotonic()
Eventlet should use time_monotonic() instead of time.time(). Example of bug of time.time(): time.sleep is affected by eventlet.monkey_patch().
For greenlet, the monotonic clock can be used with something like that:
eventlet.hubs._threadlocal.hub = eventlet.hubs.get_default_hub().Hub(monotonic_time)
time_monotonic() should be used for any function computing a timeout. Recent example: Add an optional timeout parameter to Listener.poll
Implementation
The following patch is based on the file time_monotonic.py from my Trollius project. Trollius is tested on Linux, Mac OS X, Windows, FreeBSD and OpenIndiana (which is almost Solaris): add time_monotonic() function. The reimplement reuses time.monotonic() if available.
Alternatives
- https://pypi.python.org/pypi/Monotime
- On Linux, it uses CLOCK_MONOTONIC_RAW which is wrong according to my PEP 418. Extract: "Slewing is generally desirable (i.e. we should use CLOCK_MONOTONIC, not CLOCK_MONOTONIC_RAW) if one wishes to measure "real" time (and not a time-like object like CPU cycles)."
- Monotime module doesn't support Windows nor Solaris. Does it matters for Oslo Incubator?
- It doesn't reuse time.monotonic() if available.
- python-monotonic-time
- It doesn't look to be available on PyPI: https://github.com/gavinbeatty/python-monotonic-time
