[Python-checkins] peps: PEP 418: more grammar fixes
georg.brandl
python-checkins at python.org
Sat Mar 31 08:52:59 CEST 2012
http://hg.python.org/peps/rev/39c8c00a854d
changeset: 4180:39c8c00a854d
user: Georg Brandl <georg at python.org>
date: Sat Mar 31 08:53:07 2012 +0200
summary:
PEP 418: more grammar fixes
files:
pep-0418.txt | 101 ++++++++++++++++++++------------------
1 files changed, 54 insertions(+), 47 deletions(-)
diff --git a/pep-0418.txt b/pep-0418.txt
--- a/pep-0418.txt
+++ b/pep-0418.txt
@@ -23,20 +23,22 @@
Use cases:
* Display the current time to a human (e.g. display a calendar or draw
- a wall clock): use system clock. time.time() or
- datetime.datetime.now()
-* Benchmark, profiling, timeout: time.highres()
-* Event scheduler: time.monotonic(), or time.monotonic(fallback=False)
+ a wall clock): use system clock, i.e. time.time() or
+ datetime.datetime.now().
+* Benchmark, profiling, timeout: time.highres().
+* Event scheduler: time.monotonic(), or time.monotonic(fallback=False).
Functions
=========
-* time.time(): system clock, "wall clock"
-* time.highres(): clock with the best accuracy
+To fulfill the use cases, the functions' properties are:
+
+* time.time(): system clock, "wall clock".
+* time.highres(): clock with the best accuracy.
* time.monotonic(fallback=True): monotonic clock. If no monotonic
clock is available, falls back to system clock by default, or raises
- an OSError if *fallback* is False. time.monotonic(fallback=True)
+ an OSError if *fallback* is False. time.monotonic(fallback=True)
cannot go backward.
@@ -45,7 +47,7 @@
The system time is the "wall clock". It can be set manually by the
system administrator or automatically by a NTP daemon. It can jump
-backward and forward. It is not monotonic.
+backward and forward. It is not monotonic.
It is available on all platforms and cannot fail.
@@ -90,10 +92,10 @@
available or if the monotonic clock failed, and so it cannot fail. If
fallback is False, it raises OSError if the monotonic clock failed and
NotImplementedError if the platform does not provide a monotonic clock
-(ex: GNU/Hurd).
+(e.g. on GNU/Hurd).
The elapsed time may or may not include time the system spends in
-sleep or hibernation, it depends on the operating system.
+sleep or hibernation; this depends on the operating system.
Pseudo-code [#pseudo]_::
@@ -165,17 +167,17 @@
raise NotImplementedError("you platform does not provide any monotonic clock")
return time.time()
-On Windows, QueryPerformanceCounter() is not used even if it has a
+On Windows, QueryPerformanceCounter() is not used even though it has a
better resolution than GetTickCount(). It is not reliable and has too
-much issues.
+many issues.
.. note::
time.monotonic() detects GetTickCount() integer overflow (32 bits,
roll-over after 49.7 days): it increases a delta by 2\ :sup:`32`
each time than an overflow is detected. The delta is stored in the
- process local state and so time.monotonic() value may be different
- in two Python processes.
+ process-local state and so the value of time.monotonic() may be
+ different in two Python processes.
time.highres()
@@ -250,11 +252,11 @@
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
+mach_timebase_info() is always equal to one and never fails, even
if the function may fail according to its prototype.
-mach_absolute_time() stops during a sleep on PowerPC CPU, but not on
-Intel CPU: `Different behaviour of mach_absolute_time() on i386 / ppc
+mach_absolute_time() stops during a sleep on a PowerPC CPU, but not on
+an Intel CPU: `Different behaviour of mach_absolute_time() on i386/ppc
<http://lists.apple.com/archives/PerfOptimization-dev/2006/Jul/msg00024.html>`_.
mach_absolute_time() has a resolution of 1 nanosecond.
@@ -262,8 +264,8 @@
CLOCK_MONOTONIC, CLOCK_MONOTONIC_RAW
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-CLOCK_MONOTONIC and CLOCK_MONOTONIC_RAW represents monotonic time
-since some unspecified starting point. They cannot be set.
+CLOCK_MONOTONIC and CLOCK_MONOTONIC_RAW represent monotonic time since
+some unspecified starting point. They cannot be set.
Documentation: refer to the manual page of your operating system.
Examples:
@@ -291,22 +293,23 @@
is not subject to NTP adjustments. CLOCK_MONOTONIC_RAW requires Linux
2.6.28 or later.
-On Linux, NTP may adjust CLOCK_MONOTONIC rate, but not jump backward.
-If available, CLOCK_MONOTONIC_RAW should be used instead of
+On Linux, NTP may adjust the CLOCK_MONOTONIC rate, but it cannot jump
+backward. If available, CLOCK_MONOTONIC_RAW should be used instead of
CLOCK_MONOTONIC to avoid the NTP adjustment.
CLOCK_MONOTONIC stops while the machine is suspended.
clock_gettime() fails if the system does not support the specified
-clock, whereas the standard C library supports it. For example,
+clock, even if the standard C library supports it. For example,
CLOCK_MONOTONIC_RAW 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 to the rt (real-time)
- library.
+
+ clock_gettime() requires to link the program against the rt
+ (real-time) library.
Windows: QueryPerformanceCounter
@@ -315,7 +318,7 @@
High-resolution performance counter. It is monotonic.
QueryPerformanceFrequency() gives its frequency.
-It has much higher resolution, but has lower long term accuracy than
+It has a much higher resolution, but has lower long term accuracy than
GetTickCount() and timeGetTime() clocks. For example, it will drift
compared to the low precision clocks.
@@ -330,9 +333,9 @@
* Windows XP: RDTSC instruction of Intel processors, the clock
frequency is the frequency of the processor (between 200 MHz and 3
- GHz, usually greater than 1 GHz nowadays)
-* Windows 2000: ACPI power management timer, frequency = 3,549,545
- Hz. It can be forced through the "/usepmtimer" flag in boot.ini
+ GHz, usually greater than 1 GHz nowadays).
+* Windows 2000: ACPI power management timer, frequency = 3,549,545 Hz.
+ It can be forced through the "/usepmtimer" flag in boot.ini.
.. * Windows 95/98: 8245 PIT chipset, frequency = 1,193,181 Hz
@@ -344,12 +347,12 @@
QueryPerformanceCounter() cannot be adjusted:
`SetSystemTimeAdjustment()
<http://msdn.microsoft.com/en-us/library/windows/desktop/ms724943(v=vs.85).aspx>`_
-does only adjust the system time.
+only adjusts the system time.
Bugs:
* The performance counter value may unexpectedly leap forward because
- of a hardware bug, see the `KB274323`_.
+ of a hardware bug, see `KB274323`_.
* On VirtualBox, QueryPerformanceCounter() does not increment the high
part every time the low part overflows, see `Monotonic timers
<http://code-factor.blogspot.fr/2009/11/monotonic-timers.html>`_
@@ -375,13 +378,13 @@
`GetTickCount64()
<http://msdn.microsoft.com/en-us/library/windows/desktop/ms724411(v=vs.85).aspx>`_.
-The elapsed time retrieved by GetTickCount or GetTickCount64 includes
-time the system spends in sleep or hibernation.
+The elapsed time retrieved by GetTickCount() or GetTickCount64()
+includes time the system spends in sleep or hibernation.
GetTickCount64() was added to Windows Vista and Windows Server 2008.
The clock resolution is 1 millisecond. Its accuracy is usually around
-15 ms. It is possible to improve the accuracy using the `undocumented
+15 ms. It is possible to improve the accuracy using the `undocumented
NtSetTimerResolution() function
<http://undocumented.ntinternals.net/UserMode/Undocumented%20Functions/Time/NtSetTimerResolution.html>`_.
There are applications using this undocumented function, example:
@@ -392,7 +395,7 @@
^^^^^^^^^^^^^^^^^^^^
The timeGetTime function retrieves the system time, in milliseconds.
-The system time is the time elapsed since Windows was started. Read
+The system time is the time elapsed since Windows was started. Read
the `timeGetTime() documentation
<http://msdn.microsoft.com/en-us/library/windows/desktop/dd757629(v=vs.85).aspx>`_.
@@ -408,15 +411,16 @@
consumption.
.. note::
+
timeGetTime() and timeBeginPeriod() are part the Windows multimedia
- library and so require to link the program with winmm or to load
- dynamically the library.
+ library and so require to link the program against winmm or to
+ dynamically load the library.
Solaris: CLOCK_HIGHRES
^^^^^^^^^^^^^^^^^^^^^^
-The Solaris OS has an CLOCK_HIGHRES timer that attempts to use an
+The Solaris OS has a CLOCK_HIGHRES timer that attempts to use an
optimal hardware source, and may give close to nanosecond resolution.
CLOCK_HIGHRES is the nonadjustable, high-resolution clock. For timers
created with a clockid_t value of CLOCK_HIGHRES, the system will
@@ -468,7 +472,7 @@
The system time resolution can be read using
GetSystemTimeAdjustment(). The accuracy is usually between 1
-millisecond and 15 milliseconds. Resolution:
+millisecond and 15 milliseconds. Resolution:
* GetSystemTimeAsFileTime(): 100 nanoseconds
* ftime(): 1 millisecond
@@ -508,7 +512,7 @@
* clock():
* Windows: The elapsed wall-clock time since the start of the
- process (elapsed time in seconds times CLOCKS_PER_SEC). It can
+ process (elapsed time in seconds times CLOCKS_PER_SEC). It can
fail.
* UNIX: returns an approximation of processor time used by the
program.
@@ -519,10 +523,11 @@
Resolution:
* clock() rate is CLOCKS_PER_SEC. It was called CLK_TCK in Microsoft
- C before 6.0. On Linux 3, clock() has a resolution of 1 microsecond
+ C before 6.0. On Linux 3, clock() has a resolution of 1
+ microsecond.
* The clock resolution can be read using clock_getres().
- clock_getres(CLOCK_REALTIME) is 1 nanosecond on Linux
-* GetProcessTimes(): call GetSystemTimeAdjustment()
+ clock_getres(CLOCK_REALTIME) is 1 nanosecond on Linux.
+* GetProcessTimes(): call GetSystemTimeAdjustment().
Thread
^^^^^^
@@ -553,14 +558,16 @@
QueryUnbiasedInterruptTime() was introduced in Windows 7.
+
Linux timers
------------
There were 4 implementations of the time in the Linux kernel: UTIME
-(1996), timer wheel (1997), HRT (2001) and hrtimers (2007). The later
-is the result of the "high-res-timers" project started by George
-Anzinger in 2001, contributed by Thomas Gleixner and Douglas Niehaus.
-hrtimers implementation was merged into Linux 2.6.21 released in 2007.
+(1996), timer wheel (1997), HRT (2001) and hrtimers (2007). The
+latter is the result of the "high-res-timers" project started by
+George Anzinger in 2001, with contributions by Thomas Gleixner and
+Douglas Niehaus. hrtimers implementation was merged into Linux
+2.6.21, released in 2007.
hrtimers supports various clock sources. It sets a priority to each
source to decide which one will be used.
@@ -642,7 +649,7 @@
* Virtual machines provide less reliable clocks.
* QueryPerformanceCounter() has known bugs (only one is not fixed yet)
-Python may only workaround a specific known operating system bug:
+Python may only work around a specific known operating system bug:
`KB274323`_ contains a code example to workaround the bug (use
GetTickCount() to detect QueryPerformanceCounter() leap).
--
Repository URL: http://hg.python.org/peps
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