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PEP 418: Add precision in Python; clock() will not be removed; add users

This commit is contained in:
Victor Stinner 2012-04-13 22:07:36 +02:00
parent afc9ba4a20
commit 5837b185c5
2 changed files with 111 additions and 47 deletions
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103
pep-0418.txt
View File

@ -58,9 +58,20 @@ New functions:
period
* ``time.process_time()``: profiling, CPU time of the process
``time.clock()`` is deprecated by this PEP because it is not portable:
``time.perf_counter()`` or ``time.process_time()`` should be used
instead, depending on your requirements.
Users of new functions:
* time.monotonic(): concurrent.futures, multiprocessing, queue, subprocess,
telnet and threading modules to implement timeout
* time.perf_counter(): trace and timeit modules, pybench program
* time.process_time(): profile module
* time.get_clock_info(): pybench program to display information about the
timer like the precision or the resolution
The ``time.clock()`` function is deprecated by this PEP because it is not
portable: it behaves differently depending on the operating system.
``time.perf_counter()`` or ``time.process_time()`` should be used instead,
depending on your requirements. ``time.clock()`` is marked as deprecated but
is not planned for removal.
Python functions
@ -84,7 +95,7 @@ Return a dictionary with the following keys:
* Mandatory keys:
* "function" (str): name of the underlying operating system
* "implementation" (str): name of the underlying operating system
function. Examples: "QueryPerformanceCounter()",
"clock_gettime(CLOCK_REALTIME)".
* "resolution" (float): resolution in seconds of the clock
@ -105,7 +116,7 @@ clock updates. The reference point of the returned value is
undefined, so that only the difference between the results of
consecutive calls is valid.
Availability: Windows, Mac OS X, Unix.
Availability: Windows, Mac OS X, Unix, Solaris. Not available on GNU/Hurd.
Pseudo-code [#pseudo]_::
@ -710,18 +721,18 @@ timeGetTime() 1 ms No Yes ?
Examples of clock precision on x86_64:
========================= ================ ===============
Name Operating system Precision
========================= ================ ===============
CLOCK_MONOTONIC_RAW Linux 3.2 1 ns
CLOCK_MONOTONIC Linux 3.2 1 ns
CLOCK_HIGHRES SunOS 5.11 2 ns
CLOCK_MONOTONIC SunOS 5.11 2 ns
QueryPerformanceCounter Windows Seven 10 ns
CLOCK_MONOTONIC FreeBSD 8.2 11 ns
CLOCK_MONOTONIC OpenBSD 5.0 10 ms
GetTickCount Windows Seven 15.6 ms
========================= ================ ===============
========================= ================ ========= ===================
Name Operating system Precision Precision in Python
========================= ================ ========= ===================
CLOCK_MONOTONIC_RAW Linux 3.2 1 ns 3.0 µs
CLOCK_MONOTONIC Linux 3.2 1 ns 1.6 µs
CLOCK_HIGHRES SunOS 5.11 2 ns ?
CLOCK_MONOTONIC SunOS 5.11 2 ns ?
QueryPerformanceCounter Windows Seven 10 ns ?
CLOCK_MONOTONIC FreeBSD 8.2 11 ns ?
CLOCK_MONOTONIC OpenBSD 5.0 10 ms ?
GetTickCount Windows Seven 15.6 ms ?
========================= ================ ========= ===================
For CLOCK_xxx clocks, the precision of this table is the result of
``clock_getres()``. It looks like Linux does not implement ``clock_getres()``
@ -886,8 +897,6 @@ Resolution <http://www.lucashale.com/timer-resolution/>`_.
WaitForSingleObject() uses the same timer as GetTickCount() with the
same precision.
GetTickCount() has an precision of 55 ms on Windows 9x.
Windows: timeGetTime
^^^^^^^^^^^^^^^^^^^^
@ -962,15 +971,15 @@ time() 1 sec Yes
Examples of clock precision on x86_64:
========================= ================ ===============
Name Operating system Precision
========================= ================ ===============
CLOCK_REALTIME Linux 3.2 1 ns
CLOCK_REALTIME FreeBSD 8.2 11 ns
CLOCK_REALTIME SunOS 5.11 10 ms
CLOCK_REALTIME OpenBSD 5.0 10 ms
GetSystemTimeAsFileTime Windows Seven 15.6 ms
========================= ================ ===============
========================= ================ ========= ===================
Name Operating system Precision Precision in Python
========================= ================ ========= ===================
CLOCK_REALTIME Linux 3.2 1 ns 1.9 µs
CLOCK_REALTIME FreeBSD 8.2 11 ns ?
CLOCK_REALTIME SunOS 5.11 10 ms ?
CLOCK_REALTIME OpenBSD 5.0 10 ms ?
GetSystemTimeAsFileTime Windows Seven 15.6 ms ?
========================= ================ ========= ===================
For CLOCK_REALTIME, the precision of this table is the result of
clock_getres(). It looks like Linux does not implement clock_getres()
@ -1030,18 +1039,18 @@ on other operating systems.
Examples of clock precision on x86_64:
========================= ================ ===============
Name Operating system Precision
========================= ================ ===============
CLOCK_PROCESS_CPUTIME_ID Linux 3.2 1 ns
clock() SunOS 5.11 1 µs
getrusage() Linux 3.0 4 ms
clock() FreeBSD 8.2 7.8 ms
clock() Linux 3.2 10 ms
times() Linux 3.0 10 ms
clock() OpenBSD 5.0 10 ms
GetProcessTimes() Windows Seven 15.6 ms
========================= ================ ===============
========================= ================ ========= ===================
Name Operating system Precision Precision in Python
========================= ================ ========= ===================
CLOCK_PROCESS_CPUTIME_ID Linux 3.2 1 ns 3.3 µs
clock() SunOS 5.11 1 µs ?
getrusage() Linux 3.0 4 ms 4 ms
clock() FreeBSD 8.2 7.8 ms ?
clock() Linux 3.2 1 µs 10 ms
times() Linux 3.0 10 ms 10 ms
clock() OpenBSD 5.0 10 ms ?
GetProcessTimes() Windows Seven 15.6 ms ?
========================= ================ ========= ===================
The precision of clock() in this table is the result of 1 /
CLOCKS_PER_SEC. The precision of times() in this table is the result of 1 /
@ -1090,13 +1099,13 @@ CLOCK_THREAD_CPUTIME_ID 1 ns
Examples of clock precision on x86_64:
========================= ================ ===============
Name Operating system Precision
========================= ================ ===============
CLOCK_THREAD_CPUTIME_ID Linux 3.2 1 ns
CLOCK_THREAD_CPUTIME_ID FreeBSD 8.2 1 µs
GetThreadTimes() Windows Seven 15.6 ms
========================= ================ ===============
========================= ================ =============== ===================
Name Operating system Precision Precision in Python
========================= ================ =============== ===================
CLOCK_THREAD_CPUTIME_ID Linux 3.2 1 ns ?
CLOCK_THREAD_CPUTIME_ID FreeBSD 8.2 1 µs ?
GetThreadTimes() Windows Seven 15.6 ms ?
========================= ================ =============== ===================
For CLOCK_THREAD_CPUTIME_ID, the precision of this table is the result
of clock_getres(). It looks like Linux does not implement

55
pep-0418/clock_precision.py Normal file
View File

@ -0,0 +1,55 @@
import time
def compute_precision(func):
previous = func()
precision = None
points = 0
min_points = 100
while points < min_points:
value = func()
if value == previous:
continue
dt = value - previous
previous = value
if precision is not None:
precision = min(precision, dt)
else:
precision = dt
if precision < 10e-6:
min_points = 5000
elif precision < 1e-3:
min_points = 1000
points += 1
return dt
def format_duration(dt):
if dt >= 1e-3:
return "%.1f ms" % (dt * 1e3)
if dt >= 1e-6:
return "%.1f µs" % (dt * 1e6)
else:
return "%.1f ns" % (dt * 1e9)
def test_clock(name, func):
precision = compute_precision(func)
print("%s:" % name)
print("- precision in Python: %s" % format_duration(precision))
for name in ('clock', 'perf_counter', 'process_time', 'monotonic', 'time'):
func = getattr(time, name)
test_clock("%s()" % name, func)
info = time.get_clock_info(name)
if 'precision' in info:
print("- announced precision: %s" % format_duration(info['precision']))
print("- function: %s" % info['function'])
print("- resolution: %s" % format_duration(info['resolution']))
clock_ids = [name for name in dir(time) if name.startswith("CLOCK_")]
for clock_id_text in clock_ids:
clock_id = getattr(time, clock_id_text)
name = 'clock_gettime(%s)' % clock_id_text
def gettime():
return time.clock_gettime(clock_id)
test_clock(name, gettime)