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PEP 418: QueryPerformanceCounter() has a known bug

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Victor Stinner 2012-03-29 01:11:16 +02:00
parent c0a8e14174
commit 1590fd155a
1 changed files with 16 additions and 5 deletions
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pep-0418.txt
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@ -240,15 +240,21 @@ High-resolution performance counter. It is monotonic.
QueryPerformanceFrequency() gives its frequency. QueryPerformanceFrequency() gives its frequency.
On Windows XP, QueryPerformanceFrequency() is the processor frequency and On Windows XP, QueryPerformanceFrequency() is the processor frequency and
QueryPerformanceCounter() is the TSC of the current processor. Windows XP QueryPerformanceCounter() is the TSC of the current processor.
had a bug (see `KB896256 <http://support.microsoft.com/?id=896256>`_): on a
multiprocessor computer, QueryPerformanceCounter() returned a different value The performance counter value may unexpectedly leap forward because of a
for each processor. hardware bug, see the `KB274323`_.
Windows XP had a bug (see `KB896256`_): on a multiprocessor computer,
QueryPerformanceCounter() returned a different value for each processor.
QueryPerformanceFrequency() should only be called once: the frequency will not QueryPerformanceFrequency() should only be called once: the frequency will not
change while the system is running. It fails if the installed hardware does not change while the system is running. It fails if the installed hardware does not
support a high-resolution performance counter. support a high-resolution performance counter.
.. _KB896256: http://support.microsoft.com/?id=896256
.. _KB274323: http://support.microsoft.com/?id=274323
Windows: GetTickCount(), GetTickCount64() Windows: GetTickCount(), GetTickCount64()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@ -428,7 +434,12 @@ static variable, it might be interesting to use this to make sure that the
values returned are indeed monotonic. values returned are indeed monotonic.
* Virtual machines provide less reliable clocks. * Virtual machines provide less reliable clocks.
* QueryPerformanceCounter() had a bug in 2006 on multiprocessor computers * QueryPerformanceCounter() has two known bugs:
`KB896256`_ (fixed) and `KB274323`_
Python may only workaround a specific known operating system bug: `KB274323`_
contains a code example to workaround the bug (use GetTickCount() to detect
QueryPerformanceCounter() leap).
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