[Python-checkins] bpo-37205: time.perf_counter() and time.monotonic() are system-wide (GH-23284)

Mon Nov 16 07:22:20 EST 2020

https://github.com/python/cpython/commit/3df5c68487df9d1d20ab0cd06e7942a4f96d40a4
commit: 3df5c68487df9d1d20ab0cd06e7942a4f96d40a4
branch: master
author: Victor Stinner <vstinner at python.org>
committer: vstinner <vstinner at python.org>
date: 2020年11月16日T13:21:45+01:00
summary:
bpo-37205: time.perf_counter() and time.monotonic() are system-wide (GH-23284)
time.perf_counter() on Windows and time.monotonic() on macOS are now
system-wide. Previously, they used an offset computed at startup to
reduce the precision loss caused by the float type. Use
time.perf_counter_ns() and time.monotonic_ns() added in Python 3.7 to
avoid this precision loss.
files:
A Misc/NEWS.d/next/Library/2020-11-14-14-34-32.bpo-37205.iDbHrw.rst
M Doc/library/time.rst
M Python/pytime.c

diff --git a/Doc/library/time.rst b/Doc/library/time.rst
index cff6320b526db..143f84b565f5e 100644
--- a/Doc/library/time.rst
+++ b/Doc/library/time.rst
@@ -166,6 +166,9 @@ Functions
 Return the time of the specified clock *clk_id*. Refer to
 :ref:`time-clock-id-constants` for a list of accepted values for *clk_id*.
 
+ Use :func:`clock_gettime_ns` to avoid the precision loss caused by the
+ :class:`float` type.
+
 .. availability:: Unix.
 
 .. versionadded:: 3.3
@@ -185,6 +188,9 @@ Functions
 Set the time of the specified clock *clk_id*. Currently,
 :data:`CLOCK_REALTIME` is the only accepted value for *clk_id*.
 
+ Use :func:`clock_settime_ns` to avoid the precision loss caused by the
+ :class:`float` type.
+
 .. availability:: Unix.
 
 .. versionadded:: 3.3
@@ -273,10 +279,17 @@ Functions
 The reference point of the returned value is undefined, so that only the
 difference between the results of consecutive calls is valid.
 
+ Use :func:`monotonic_ns` to avoid the precision loss caused by the
+ :class:`float` type.
+
 .. versionadded:: 3.3
+
 .. versionchanged:: 3.5
 The function is now always available and always system-wide.
 
+ .. versionchanged:: 3.10
+ On macOS, the function is now system-wide.
+
 
 .. function:: monotonic_ns() -> int
 
@@ -295,8 +308,14 @@ Functions
 point of the returned value is undefined, so that only the difference between
 the results of consecutive calls is valid.
 
+ Use :func:`perf_counter_ns` to avoid the precision loss caused by the
+ :class:`float` type.
+
 .. versionadded:: 3.3
 
+ .. versionchanged:: 3.10
+ On Windows, the function is now system-wide.
+
 .. function:: perf_counter_ns() -> int
 
 Similar to :func:`perf_counter`, but return time as nanoseconds.
@@ -317,6 +336,9 @@ Functions
 returned value is undefined, so that only the difference between the results
 of consecutive calls is valid.
 
+ Use :func:`process_time_ns` to avoid the precision loss caused by the
+ :class:`float` type.
+
 .. versionadded:: 3.3
 
 .. function:: process_time_ns() -> int
@@ -581,6 +603,17 @@ Functions
 :class:`struct_time` object is returned, from which the components
 of the calendar date may be accessed as attributes.
 
+ Use :func:`time_ns` to avoid the precision loss caused by the :class:`float`
+ type.
+
+
+.. function:: time_ns() -> int
+
+ Similar to :func:`~time.time` but returns time as an integer number of nanoseconds
+ since the epoch_.
+
+ .. versionadded:: 3.7
+
 
 .. function:: thread_time() -> float
 
@@ -595,6 +628,9 @@ Functions
 returned value is undefined, so that only the difference between the results
 of consecutive calls in the same thread is valid.
 
+ Use :func:`thread_time_ns` to avoid the precision loss caused by the
+ :class:`float` type.
+
 .. availability:: Windows, Linux, Unix systems supporting
 ``CLOCK_THREAD_CPUTIME_ID``.
 
@@ -608,13 +644,6 @@ Functions
 .. versionadded:: 3.7
 
 
-.. function:: time_ns() -> int
-
- Similar to :func:`~time.time` but returns time as an integer number of nanoseconds
- since the epoch_.
-
- .. versionadded:: 3.7
-
 .. function:: tzset()
 
 Reset the time conversion rules used by the library routines. The environment
diff --git a/Misc/NEWS.d/next/Library/2020-11-14-14-34-32.bpo-37205.iDbHrw.rst b/Misc/NEWS.d/next/Library/2020-11-14-14-34-32.bpo-37205.iDbHrw.rst
new file mode 100644
index 0000000000000..5cf325ec0c19d
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-11-14-14-34-32.bpo-37205.iDbHrw.rst
@@ -0,0 +1,5 @@
+:func:`time.perf_counter()` on Windows and :func:`time.monotonic()` on macOS
+are now system-wide. Previously, they used an offset computed at startup to
+reduce the precision loss caused by the float type. Use
+:func:`time.perf_counter_ns()` and :func:`time.monotonic_ns()` added in Python
+3.7 to avoid this precision loss.
diff --git a/Python/pytime.c b/Python/pytime.c
index 89d63e080422b..179bced1ac68f 100644
--- a/Python/pytime.c
+++ b/Python/pytime.c
@@ -6,7 +6,7 @@
 #if defined(__APPLE__)
 #include <mach/mach_time.h> /* mach_absolute_time(), mach_timebase_info() */
 
-#if defined(__APPLE__) && defined(__has_builtin) 
+#if defined(__APPLE__) && defined(__has_builtin)
 # if __has_builtin(__builtin_available)
 # define HAVE_CLOCK_GETTIME_RUNTIME __builtin_available(macOS 10.12, iOS 10.0, tvOS 10.0, watchOS 3.0, *)
 # endif
@@ -730,7 +730,7 @@ pygettimeofday(_PyTime_t *tp, _Py_clock_info_t *info, int raise)
 }
 
 #ifdef HAVE_CLOCK_GETTIME_RUNTIME
- } else { 
+ } else {
 #endif
 
 #endif
@@ -822,7 +822,6 @@ pymonotonic(_PyTime_t *tp, _Py_clock_info_t *info, int raise)
 
 #elif defined(__APPLE__)
 static mach_timebase_info_data_t timebase;
- static uint64_t t0 = 0;
 uint64_t ticks;
 
 if (timebase.denom == 0) {
@@ -859,8 +858,6 @@ pymonotonic(_PyTime_t *tp, _Py_clock_info_t *info, int raise)
 "mach_timebase_info is too large");
 return -1;
 }
-
- t0 = mach_absolute_time();
 }
 
 if (info) {
@@ -871,9 +868,6 @@ pymonotonic(_PyTime_t *tp, _Py_clock_info_t *info, int raise)
 }
 
 ticks = mach_absolute_time();
- /* Use a "time zero" to reduce precision loss when converting time
- to floatting point number, as in time.monotonic(). */
- ticks -= t0;
 *tp = _PyTime_MulDiv(ticks,
 (_PyTime_t)timebase.numer,
 (_PyTime_t)timebase.denom);
@@ -960,7 +954,6 @@ static int
 win_perf_counter(_PyTime_t *tp, _Py_clock_info_t *info)
 {
 static LONGLONG frequency = 0;
- static LONGLONG t0 = 0;
 LARGE_INTEGER now;
 LONGLONG ticksll;
 _PyTime_t ticks;
@@ -1000,7 +993,6 @@ win_perf_counter(_PyTime_t *tp, _Py_clock_info_t *info)
 }
 
 QueryPerformanceCounter(&now);
- t0 = now.QuadPart;
 }
 
 if (info) {
@@ -1013,10 +1005,6 @@ win_perf_counter(_PyTime_t *tp, _Py_clock_info_t *info)
 QueryPerformanceCounter(&now);
 ticksll = now.QuadPart;
 
- /* Use a "time zero" to reduce precision loss when converting time
- to floatting point number, as in time.perf_counter(). */
- ticksll -= t0;
-
 /* Make sure that casting LONGLONG to _PyTime_t cannot overflow,
 both types are signed */
 Py_BUILD_ASSERT(sizeof(ticksll) <= sizeof(ticks));
