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PEP 418: Mention the Technical Q&A QA1398 for mach_absolute_time()

This commit is contained in:
Victor Stinner 2012-03-28 02:59:01 +02:00
parent 02b9a5bcb3
commit aaa1107673
1 changed files with 13 additions and 10 deletions
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23
pep-0418.txt
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@ -137,7 +137,7 @@ system time.
It is available on all platforms and cannot fail.
Pseudo-code [#pseudo]_: ::
Pseudo-code::
def hires():
if hires.use_monotonic:
@ -158,11 +158,15 @@ Monotonic
mach_absolute_time
^^^^^^^^^^^^^^^^^^
Mac OS X provides a monotonic clock: mach_absolute_time(). mach_timebase_info()
provides a fraction to convert the clock value to a number of nanoseconds.
Mac OS X provides a monotonic clock: mach_absolute_time(). It is based on
absolute elapsed time delta since system boot. It is not adjusted and cannot be
set.
According to the documentation, mach_timebase_info() is always equals to one
and does never fail, even if the function may fail according to its prototype.
mach_timebase_info() gives a fraction to convert the clock value to a number of
nanoseconds. According to the documentation (`Technical Q&A QA1398
<https://developer.apple.com/library/mac/#qa/qa1398/>`_), mach_timebase_info()
is always equals to one and does never fail, even if the function may fail
according to its prototype.
mach_absolute_time() has a resolution of 1 nanosecond.
@ -189,7 +193,7 @@ requires a kernel version 2.6.28 or later.
clock_getres() gives the clock resolution. It is 1 nanosecond on Linux.
.. note::
clock_gettime() requires to link the program with the realtime ("rt") library.
clock_gettime() requires to link the program to the rt (real-time) library.
QueryPerformanceCounter
^^^^^^^^^^^^^^^^^^^^^^^
@ -197,7 +201,6 @@ QueryPerformanceCounter
High-resolution performance counter. It is monotonic.
QueryPerformanceFrequency() gives its frequency.
On Windows XP, QueryPerformanceFrequency() is the processor frequency and
QueryPerformanceCounter() is the TSC of the current processor. Windows XP
had a bug (see `KB896256 <http://support.microsoft.com/?id=896256>`_): on a
@ -315,9 +318,9 @@ Alternatives: API design
One function with a flag: time.monotonic(strict=False)
----------------------------------------------------------
* time.monotonic(strict=False) falls back to another clock if no monotonic clock
is not available or does not work, but it does never fail.
* time.monotonic(strict=True) raises OSError if monotonic clock fails or
* time.monotonic(strict=False) falls back to the system clock if no monotonic
clock is available or if the monotonic clock failed.
* time.monotonic(strict=True) raises OSError if monotonic clock fails and
NotImplementedError if the system does not provide a monotonic clock
"A keyword argument that gets passed as a constant in the caller is usually