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PEP 418: Stephen J. Turnbull's patch: typos

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Victor Stinner 2012-04-21 21:16:37 +02:00
parent d0166c382d
commit 9137ddbec3
1 changed files with 25 additions and 25 deletions
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@ -49,7 +49,7 @@ Each operating system implements clocks and performance counters
differently, and it is useful to know exactly which function is used differently, and it is useful to know exactly which function is used
and some properties of the clock like its resolution and its and some properties of the clock like its resolution and its
precision. The new ``time.get_clock_info()`` function gives access to precision. The new ``time.get_clock_info()`` function gives access to
all available information of each Python time function. all available information about each Python time function.
New functions: New functions:
@ -141,7 +141,7 @@ consecutive calls is valid and is a number of seconds.
On Windows versions older than Vista, ``time.monotonic()`` detects On Windows versions older than Vista, ``time.monotonic()`` detects
``GetTickCount()`` integer overflow (32 bits, roll-over after 49.7 ``GetTickCount()`` integer overflow (32 bits, roll-over after 49.7
days): it increases a delta by 2\ :sup:`32` each time than an overflow days): it increases a delta by 2\ :sup:`32` each time that an overflow
is detected. The delta is stored in the process-local state and so is detected. The delta is stored in the process-local state and so
the value of ``time.monotonic()`` may be different in two Python the value of ``time.monotonic()`` may be different in two Python
processes running for more than 49 days. On more recent versions of processes running for more than 49 days. On more recent versions of
@ -432,7 +432,7 @@ Other names for time.monotonic()
point. point.
The name "time.try_monotonic()" was also proposed for an older The name "time.try_monotonic()" was also proposed for an older
proposition of time.monotonic() which was falling back to the system version of time.monotonic() which would fall back to the system
time when no monotonic clock was available. time when no monotonic clock was available.
Other names for time.perf_counter() Other names for time.perf_counter()
@ -461,11 +461,11 @@ system time.
Issues: Issues:
* It is hard to define correctly such function in the documentation: * It is hard to define such a function correctly in the documentation:
is it monotonic? Is it steady? Is it adjusted? is it monotonic? Is it steady? Is it adjusted?
* Some user want to decide what to do when no monotonic clock is * Some users want to decide what to do when no monotonic clock is
available: use another clock, display an error, or do something available: use another clock, display an error, or do something
else? else.
Different APIs were proposed to define such function. Different APIs were proposed to define such function.
@ -499,7 +499,7 @@ the first call to time.monotonic().
Choosing the clock from a list of constraints Choosing the clock from a list of constraints
--------------------------------------------- ---------------------------------------------
The PEP as proposed offers a few new clocks, but their guarentees The PEP as proposed offers a few new clocks, but their guarantees
are deliberately loose in order to offer useful clocks on different are deliberately loose in order to offer useful clocks on different
platforms. This inherently embeds policy in the calls, and the platforms. This inherently embeds policy in the calls, and the
caller must thus choose a policy. caller must thus choose a policy.
@ -516,7 +516,7 @@ evaluate their suitability.
The primary interface is a function make simple choices easy: The primary interface is a function make simple choices easy:
the caller can use ``time.get_clock(*flags)`` with some combination of flags. the caller can use ``time.get_clock(*flags)`` with some combination of flags.
This include at least: This includes at least:
* time.MONOTONIC: clock cannot go backward * time.MONOTONIC: clock cannot go backward
* time.STEADY: clock rate is steady * time.STEADY: clock rate is steady
@ -536,7 +536,7 @@ be chained using the or operator. Example of a simple policy decision::
The available clocks always at least include a wrapper for ``time.time()``, The available clocks always at least include a wrapper for ``time.time()``,
so a final call with no flags can always be used to obtain a working clock. so a final call with no flags can always be used to obtain a working clock.
Example of flags of system clocks: Examples of flags of system clocks:
* QueryPerformanceCounter: MONOTONIC | HIGHRES * QueryPerformanceCounter: MONOTONIC | HIGHRES
* GetTickCount: MONOTONIC | STEADY * GetTickCount: MONOTONIC | STEADY
@ -606,7 +606,7 @@ Glossary
:Clock: :Clock:
An instrument for measuring time. Different clocks have different An instrument for measuring time. Different clocks have different
characteristics; for example, a clock with <nanonsecond> characteristics; for example, a clock with <nanosecond>
<precision> may start to <drift> after a few minutes, while a less <precision> may start to <drift> after a few minutes, while a less
precise clock remained accurate for days. This PEP is primarily precise clock remained accurate for days. This PEP is primarily
concerned with clocks which use a unit of seconds. concerned with clocks which use a unit of seconds.
@ -723,7 +723,7 @@ List of hardware clocks
* TSC (Time Stamp Counter): Historically, the TSC increased with every * TSC (Time Stamp Counter): Historically, the TSC increased with every
internal processor clock cycle, but now the rate is usually constant internal processor clock cycle, but now the rate is usually constant
(even if the processor changes frequency) and usually equals the (even if the processor changes frequency) and usually equals the
maximum processor frequency. Multiple cores having different TSC maximum processor frequency. Multiple cores have different TSC
values. Hibernation of system will reset TSC value. The RDTSC values. Hibernation of system will reset TSC value. The RDTSC
instruction can be used to read this counter. CPU frequency scaling instruction can be used to read this counter. CPU frequency scaling
for power saving. for power saving.
@ -734,10 +734,10 @@ List of hardware clocks
IBM "Summit" series chipsets (ex: x440). This is available in IA32 IBM "Summit" series chipsets (ex: x440). This is available in IA32
and IA64 architectures. and IA64 architectures.
* PIT (programmable interrupt timer): Intel 8253/8254 chipsets with a * PIT (programmable interrupt timer): Intel 8253/8254 chipsets with a
configurable frequency in range 18.2 Hz - 1.2 MHz. It is a 16-bit configurable frequency in range 18.2 Hz - 1.2 MHz. It uses a 16-bit
counter. counter.
* RTC (Real-time clock). Most RTCs use a crystal oscillator with a * RTC (Real-time clock). Most RTCs use a crystal oscillator with a
frequency of 32,768 Hz frequency of 32,768 Hz.
Linux clocksource Linux clocksource
@ -747,7 +747,7 @@ There were 4 implementations of the time in the Linux kernel: UTIME
(1996), timer wheel (1997), HRT (2001) and hrtimers (2007). The (1996), timer wheel (1997), HRT (2001) and hrtimers (2007). The
latter is the result of the "high-res-timers" project started by latter is the result of the "high-res-timers" project started by
George Anzinger in 2001, with contributions by Thomas Gleixner and George Anzinger in 2001, with contributions by Thomas Gleixner and
Douglas Niehaus. hrtimers implementation was merged into Linux Douglas Niehaus. The hrtimers implementation was merged into Linux
2.6.21, released in 2007. 2.6.21, released in 2007.
hrtimers supports various clock sources. It sets a priority to each hrtimers supports various clock sources. It sets a priority to each
@ -782,7 +782,7 @@ Read also the `time(7) manual page
FreeBSD timecounter FreeBSD timecounter
------------------- -------------------
kern.timecounter.choice list available hardware clocks with their kern.timecounter.choice lists available hardware clocks with their
priority. The sysctl program can be used to change the timecounter. priority. The sysctl program can be used to change the timecounter.
Example:: Example::
@ -819,7 +819,7 @@ Read `Timecounters: Efficient and precise timekeeping in SMP kernels
Performance Performance
----------- -----------
Reading an hardware clock has a cost. The following table compares Reading a hardware clock has a cost. The following table compares
the performance of different hardware clocks on Linux 3.3 with Intel the performance of different hardware clocks on Linux 3.3 with Intel
Core i7-2600 at 3.40GHz (8 cores). The `bench_time.c Core i7-2600 at 3.40GHz (8 cores). The `bench_time.c
<http://hg.python.org/peps/file/tip/pep-0418/bench_time.c>`_ program <http://hg.python.org/peps/file/tip/pep-0418/bench_time.c>`_ program
@ -864,7 +864,7 @@ CLOCK_MONOTONIC 201 ns 10766 ns 4498 ns 3943 ns
======================== ====== ========= ======= ======= ======================== ====== ========= ======= =======
Each function was called 100,000 times and CLOCK_MONOTONIC was used to Each function was called 100,000 times and CLOCK_MONOTONIC was used to
get the time before and after. The benchmark was run 5 times to keep get the time before and after. The benchmark was run 5 times, keeping
the minimum time. the minimum time.
@ -881,14 +881,14 @@ NTP has different methods to adjust a clock:
* "stepping": jump by a large amount in a single discrete step (which * "stepping": jump by a large amount in a single discrete step (which
is done with ``settimeofday()``) is done with ``settimeofday()``)
By default, the time is slewed if the offset is less than 128 ms, or By default, the time is slewed if the offset is less than 128 ms, but
stepped otherwise. stepped otherwise.
Slewing is generally desirable (i.e. we should use CLOCK_MONOTONIC, Slewing is generally desirable (i.e. we should use CLOCK_MONOTONIC,
not CLOCK_MONOTONIC_RAW) if one wishes to measure "real" time (and not not CLOCK_MONOTONIC_RAW) if one wishes to measure "real" time (and not
a time-like object like CPU cycles). This is because the clock on the a time-like object like CPU cycles). This is because the clock on the
other end of the NTP connection from you is probably better at keeping other end of the NTP connection from you is probably better at keeping
time: hopefully that thirty five thousand dollars of Cesium time: hopefully that thirty-five thousand dollars of Cesium
timekeeping goodness is doing something better than your PC's $3 timekeeping goodness is doing something better than your PC's $3
quartz crystal, after all. quartz crystal, after all.
@ -1223,7 +1223,7 @@ to CLOCK_REALTIME, less precise but faster.
Alexander Shishkin proposed an API for Linux to be notified when the system Alexander Shishkin proposed an API for Linux to be notified when the system
clock is changed: `timerfd: add TFD_NOTIFY_CLOCK_SET to watch for clock changes clock is changed: `timerfd: add TFD_NOTIFY_CLOCK_SET to watch for clock changes
<http://lwn.net/Articles/432395/>`_ (4th version of the API, March 2011). The <http://lwn.net/Articles/432395/>`_ (4th version of the API, March 2011). The
API is not accepted yet, CLOCK_BOOTTIME provides a similar feature. API is not accepted yet, but CLOCK_BOOTTIME provides a similar feature.
Process Time Process Time
@ -1291,7 +1291,7 @@ Functions
program. program.
* getrusage(RUSAGE_SELF) returns a structure of resource usage of the currenet * getrusage(RUSAGE_SELF) returns a structure of resource usage of the currenet
process. ru_utime is use CPU time and ru_stime is the system CPU time. process. ru_utime is user CPU time and ru_stime is the system CPU time.
* times(): structure of process times. The precision is 1 / ticks_per_seconds, * times(): structure of process times. The precision is 1 / ticks_per_seconds,
where ticks_per_seconds is sysconf(_SC_CLK_TCK) or the HZ constant. where ticks_per_seconds is sysconf(_SC_CLK_TCK) or the HZ constant.
@ -1466,11 +1466,11 @@ Other functions
System Standby System Standby
============== ==============
The ACPI power state "S3" is as system standby mode, also called The ACPI power state "S3" is a system standby mode, also called
"Suspend to RAM". RAM remains powered. "Suspend to RAM". RAM remains powered.
On Windows, the ``WM_POWERBROADCAST`` message is send to Windows On Windows, the ``WM_POWERBROADCAST`` message is sent to Windows
application to notify them of power-management events (ex: ower status applications to notify them of power-management events (ex: owner status
has changed). has changed).
For Mac OS X, read `Registering and unregistering for sleep and wake For Mac OS X, read `Registering and unregistering for sleep and wake
@ -1484,7 +1484,7 @@ Footnotes
.. [#pseudo] "_time" is an hypothetical module only used for the example. .. [#pseudo] "_time" is an hypothetical module only used for the example.
The time module is implemented in C and so there is no need for The time module is implemented in C and so there is no need for
such module. such a module.
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