gh-110850: Add PyTime_t C API (GH-115215)

* gh-110850: Add PyTime_t C API

Add PyTime_t API:

* PyTime_t type.
* PyTime_MIN and PyTime_MAX constants.
* PyTime_AsSecondsDouble(), PyTime_Monotonic(),
  PyTime_PerfCounter() and PyTime_GetSystemClock() functions.

Co-authored-by: Victor Stinner <[email protected]>

Author: encukou

Doc/c-api/time.rst

@@ -0,0 +1,83 @@
+.. highlight:: c
+
+PyTime C API
+============
+
+.. versionadded:: 3.13
+
+The clock C API provides access to system clocks.
+It is similar to the Python :mod:`time` module.
+
+For C API related to the :mod:`datetime` module, see :ref:`datetimeobjects`.
+
+
+Types
+-----
+
+.. c:type:: PyTime_t
+
+   A timestamp or duration in nanoseconds, represented as a signed 64-bit
+   integer.
+
+   The reference point for timestamps depends on the clock used. For example,
+   :c:func:`PyTime_Time` returns timestamps relative to the UNIX epoch.
+
+   The supported range is around [-292.3 years; +292.3 years].
+   Using the Unix epoch (January 1st, 1970) as reference, the supported date
+   range is around [1677-09-21; 2262-04-11].
+   The exact limits are exposed as constants:
+
+.. c:var:: PyTime_t PyTime_MIN
+
+   Minimum value of :c:type:`PyTime_t`.
+
+.. c:var:: PyTime_t PyTime_MAX
+
+   Maximum value of :c:type:`PyTime_t`.
+
+
+Clock Functions
+---------------
+
+The following functions take a pointer to a :c:expr:`PyTime_t` that they
+set to the value of a particular clock.
+Details of each clock are given in the documentation of the corresponding
+Python function.
+
+The functions return ``0`` on success, or ``-1`` (with an exception set)
+on failure.
+
+On integer overflow, they set the :c:data:`PyExc_OverflowError` exception and
+set ``*result`` to the value clamped to the ``[PyTime_MIN; PyTime_MAX]``
+range.
+(On current systems, integer overflows are likely caused by misconfigured
+system time.)
+
+As any other C API (unless otherwise specified), the functions must be called
+with the :term:`GIL` held.
+
+.. c:function:: int PyTime_Monotonic(PyTime_t *result)
+
+   Read the monotonic clock.
+   See :func:`time.monotonic` for important details on this clock.
+
+.. c:function:: int PyTime_PerfCounter(PyTime_t *result)
+
+   Read the performance counter.
+   See :func:`time.perf_counter` for important details on this clock.
+
+.. c:function:: int PyTime_Time(PyTime_t *result)
+
+   Read the “wall clock” time.
+   See :func:`time.time` for details important on this clock.
+
+
+Conversion functions
+--------------------
+
+.. c:function:: double PyTime_AsSecondsDouble(PyTime_t t)
+
+   Convert a timestamp to a number of seconds as a C :c:expr:`double`.
+
+   The function cannot fail, but note that :c:expr:`double` has limited
+   accuracy for large values.

Doc/c-api/utilities.rst

@@ -20,4 +20,5 @@ and parsing function arguments and constructing Python values from C values.
    hash.rst
    reflection.rst
    codec.rst
+   time.rst
    perfmaps.rst

Doc/conf.py

@@ -135,11 +135,14 @@
     ('c:type', 'wchar_t'),
     ('c:type', '__int64'),
     ('c:type', 'unsigned __int64'),
+    ('c:type', 'double'),
     # Standard C structures
     ('c:struct', 'in6_addr'),
     ('c:struct', 'in_addr'),
     ('c:struct', 'stat'),
     ('c:struct', 'statvfs'),
+    ('c:struct', 'timeval'),
+    ('c:struct', 'timespec'),
     # Standard C macros
     ('c:macro', 'LLONG_MAX'),
     ('c:macro', 'LLONG_MIN'),
@@ -269,12 +272,12 @@
     ('py:meth', 'index'),  # list.index, tuple.index, etc.
 ]
 
-# gh-106948: Copy standard C types declared in the "c:type" domain to the
-# "c:identifier" domain, since "c:function" markup looks for types in the
-# "c:identifier" domain. Use list() to not iterate on items which are being
-# added
+# gh-106948: Copy standard C types declared in the "c:type" domain and C
+# structures declared in the "c:struct" domain to the "c:identifier" domain,
+# since "c:function" markup looks for types in the "c:identifier" domain. Use
+# list() to not iterate on items which are being added
 for role, name in list(nitpick_ignore):
-    if role == 'c:type':
+    if role in ('c:type', 'c:struct'):
         nitpick_ignore.append(('c:identifier', name))
 del role, name
 

Doc/whatsnew/3.13.rst

@@ -1516,6 +1516,16 @@ New Features
 * Add :c:func:`Py_HashPointer` function to hash a pointer.
   (Contributed by Victor Stinner in :gh:`111545`.)
 
+* Add PyTime C API:
+
+  * :c:type:`PyTime_t` type.
+  * :c:var:`PyTime_MIN` and :c:var:`PyTime_MAX` constants.
+  * :c:func:`PyTime_AsSecondsDouble`
+    :c:func:`PyTime_Monotonic`, :c:func:`PyTime_PerfCounter`, and
+    :c:func:`PyTime_Time` functions.
+
+  (Contributed by Victor Stinner and Petr Viktorin in :gh:`110850`.)
+
 
 Porting to Python 3.13
 ----------------------

Include/Python.h

@@ -97,6 +97,7 @@
 #include "weakrefobject.h"
 #include "structseq.h"
 #include "cpython/picklebufobject.h"
+#include "cpython/pytime.h"
 #include "codecs.h"
 #include "pyerrors.h"
 #include "pythread.h"

Include/cpython/pytime.h

@@ -0,0 +1,23 @@
+// PyTime_t C API: see Doc/c-api/time.rst for the documentation.
+
+#ifndef Py_LIMITED_API
+#ifndef Py_PYTIME_H
+#define Py_PYTIME_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef int64_t PyTime_t;
+#define PyTime_MIN INT64_MIN
+#define PyTime_MAX INT64_MAX
+
+PyAPI_FUNC(double) PyTime_AsSecondsDouble(PyTime_t t);
+PyAPI_FUNC(int) PyTime_Monotonic(PyTime_t *result);
+PyAPI_FUNC(int) PyTime_PerfCounter(PyTime_t *result);
+PyAPI_FUNC(int) PyTime_Time(PyTime_t *result);
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* Py_PYTIME_H */
+#endif /* Py_LIMITED_API */

Include/internal/pycore_time.h

@@ -1,45 +1,51 @@
-// The _PyTime_t API is written to use timestamp and timeout values stored in
-// various formats and to read clocks.
+// Internal PyTime_t C API: see Doc/c-api/time.rst for the documentation.
 //
-// The _PyTime_t type is an integer to support directly common arithmetic
-// operations like t1 + t2.
+// The PyTime_t type is an integer to support directly common arithmetic
+// operations such as t1 + t2.
 //
-// The _PyTime_t API supports a resolution of 1 nanosecond. The _PyTime_t type
-// is signed to support negative timestamps. The supported range is around
-// [-292.3 years; +292.3 years]. Using the Unix epoch (January 1st, 1970), the
-// supported date range is around [1677-09-21; 2262-04-11].
+// Time formats:
 //
-// Formats:
+// * Seconds.
+// * Seconds as a floating point number (C double).
+// * Milliseconds (10^-3 seconds).
+// * Microseconds (10^-6 seconds).
+// * 100 nanoseconds (10^-7 seconds), used on Windows.
+// * Nanoseconds (10^-9 seconds).
+// * timeval structure, 1 microsecond (10^-6 seconds).
+// * timespec structure, 1 nanosecond (10^-9 seconds).
 //
-// * seconds
-// * seconds as a floating pointer number (C double)
-// * milliseconds (10^-3 seconds)
-// * microseconds (10^-6 seconds)
-// * 100 nanoseconds (10^-7 seconds)
-// * nanoseconds (10^-9 seconds)
-// * timeval structure, 1 microsecond resolution (10^-6 seconds)
-// * timespec structure, 1 nanosecond resolution (10^-9 seconds)
+// Note that PyTime_t is now specified as int64_t, in nanoseconds.
+// (If we need to change this, we'll need new public API with new names.)
+// Previously, PyTime_t was configurable (in theory); some comments and code
+// might still allude to that.
 //
 // Integer overflows are detected and raise OverflowError. Conversion to a
-// resolution worse than 1 nanosecond is rounded correctly with the requested
-// rounding mode. There are 4 rounding modes: floor (towards -inf), ceiling
-// (towards +inf), half even and up (away from zero).
+// resolution larger than 1 nanosecond is rounded correctly with the requested
+// rounding mode. Available rounding modes:
 //
-// Some functions clamp the result in the range [_PyTime_MIN; _PyTime_MAX], so
-// the caller doesn't have to handle errors and doesn't need to hold the GIL.
-// For example, _PyTime_Add(t1, t2) computes t1+t2 and clamp the result on
-// overflow.
+// * Round towards minus infinity (-inf). For example, used to read a clock.
+// * Round towards infinity (+inf). For example, used for timeout to wait "at
+//   least" N seconds.
+// * Round to nearest with ties going to nearest even integer. For example, used
+//   to round from a Python float.
+// * Round away from zero. For example, used for timeout.
+//
+// Some functions clamp the result in the range [PyTime_MIN; PyTime_MAX]. The
+// caller doesn't have to handle errors and so doesn't need to hold the GIL to
+// handle exceptions. For example, _PyTime_Add(t1, t2) computes t1+t2 and
+// clamps the result on overflow.
 //
 // Clocks:
 //
 // * System clock
 // * Monotonic clock
 // * Performance counter
 //
-// Operations like (t * k / q) with integers are implemented in a way to reduce
-// the risk of integer overflow. Such operation is used to convert a clock
-// value expressed in ticks with a frequency to _PyTime_t, like
-// QueryPerformanceCounter() with QueryPerformanceFrequency().
+// Internally, operations like (t * k / q) with integers are implemented in a
+// way to reduce the risk of integer overflow. Such operation is used to convert a
+// clock value expressed in ticks with a frequency to PyTime_t, like
+// QueryPerformanceCounter() with QueryPerformanceFrequency() on Windows.
+
 
 #ifndef Py_INTERNAL_TIME_H
 #define Py_INTERNAL_TIME_H
@@ -56,14 +62,7 @@ extern "C" {
 struct timeval;
 #endif
 
-// _PyTime_t: Python timestamp with subsecond precision. It can be used to
-// store a duration, and so indirectly a date (related to another date, like
-// UNIX epoch).
-typedef int64_t _PyTime_t;
-// _PyTime_MIN nanoseconds is around -292.3 years
-#define _PyTime_MIN INT64_MIN
-// _PyTime_MAX nanoseconds is around +292.3 years
-#define _PyTime_MAX INT64_MAX
+typedef PyTime_t _PyTime_t;
 #define _SIZEOF_PYTIME_T 8
 
 typedef enum {
@@ -147,7 +146,7 @@ PyAPI_FUNC(_PyTime_t) _PyTime_FromSecondsDouble(double seconds, _PyTime_round_t
 PyAPI_FUNC(_PyTime_t) _PyTime_FromNanoseconds(_PyTime_t ns);
 
 // Create a timestamp from a number of microseconds.
-// Clamp to [_PyTime_MIN; _PyTime_MAX] on overflow.
+// Clamp to [PyTime_MIN; PyTime_MAX] on overflow.
 extern _PyTime_t _PyTime_FromMicrosecondsClamp(_PyTime_t us);
 
 // Create a timestamp from nanoseconds (Python int).
@@ -169,10 +168,6 @@ PyAPI_FUNC(int) _PyTime_FromMillisecondsObject(_PyTime_t *t,
     PyObject *obj,
     _PyTime_round_t round);
 
-// Convert a timestamp to a number of seconds as a C double.
-// Export for '_socket' shared extension.
-PyAPI_FUNC(double) _PyTime_AsSecondsDouble(_PyTime_t t);
-
 // Convert timestamp to a number of milliseconds (10^-3 seconds).
 // Export for '_ssl' shared extension.
 PyAPI_FUNC(_PyTime_t) _PyTime_AsMilliseconds(_PyTime_t t,
@@ -183,9 +178,6 @@ PyAPI_FUNC(_PyTime_t) _PyTime_AsMilliseconds(_PyTime_t t,
 PyAPI_FUNC(_PyTime_t) _PyTime_AsMicroseconds(_PyTime_t t,
     _PyTime_round_t round);
 
-// Convert timestamp to a number of nanoseconds (10^-9 seconds).
-extern _PyTime_t _PyTime_AsNanoseconds(_PyTime_t t);
-
 #ifdef MS_WINDOWS
 // Convert timestamp to a number of 100 nanoseconds (10^-7 seconds).
 extern _PyTime_t _PyTime_As100Nanoseconds(_PyTime_t t,
@@ -250,7 +242,7 @@ PyAPI_FUNC(void) _PyTime_AsTimespec_clamp(_PyTime_t t, struct timespec *ts);
 #endif
 
 
-// Compute t1 + t2. Clamp to [_PyTime_MIN; _PyTime_MAX] on overflow.
+// Compute t1 + t2. Clamp to [PyTime_MIN; PyTime_MAX] on overflow.
 extern _PyTime_t _PyTime_Add(_PyTime_t t1, _PyTime_t t2);
 
 // Structure used by time.get_clock_info()
@@ -267,7 +259,8 @@ typedef struct {
 // On integer overflow, silently ignore the overflow and clamp the clock to
 // [_PyTime_MIN; _PyTime_MAX].
 //
-// Use _PyTime_GetSystemClockWithInfo() to check for failure.
+// Use _PyTime_GetSystemClockWithInfo or the public PyTime_Time() to check
+// for failure.
 // Export for '_random' shared extension.
 PyAPI_FUNC(_PyTime_t) _PyTime_GetSystemClock(void);
 
@@ -287,7 +280,8 @@ extern int _PyTime_GetSystemClockWithInfo(
 // On integer overflow, silently ignore the overflow and clamp the clock to
 // [_PyTime_MIN; _PyTime_MAX].
 //
-// Use _PyTime_GetMonotonicClockWithInfo() to check for failure.
+// Use _PyTime_GetMonotonicClockWithInfo or the public PyTime_Monotonic()
+// to check for failure.
 // Export for '_random' shared extension.
 PyAPI_FUNC(_PyTime_t) _PyTime_GetMonotonicClock(void);
 
@@ -322,10 +316,12 @@ PyAPI_FUNC(int) _PyTime_gmtime(time_t t, struct tm *tm);
 // On integer overflow, silently ignore the overflow and clamp the clock to
 // [_PyTime_MIN; _PyTime_MAX].
 //
-// Use _PyTime_GetPerfCounterWithInfo() to check for failure.
+// Use _PyTime_GetPerfCounterWithInfo() or the public PyTime_PerfCounter
+// to check for failure.
 // Export for '_lsprof' shared extension.
 PyAPI_FUNC(_PyTime_t) _PyTime_GetPerfCounter(void);
 
+
 // Get the performance counter: clock with the highest available resolution to
 // measure a short duration.
 //
@@ -336,6 +332,13 @@ extern int _PyTime_GetPerfCounterWithInfo(
     _PyTime_t *t,
     _Py_clock_info_t *info);
 
+// Alias for backward compatibility
+#define _PyTime_MIN PyTime_MIN
+#define _PyTime_MAX PyTime_MAX
+#define _PyTime_AsSecondsDouble PyTime_AsSecondsDouble
+
+
+// --- _PyDeadline -----------------------------------------------------------
 
 // Create a deadline.
 // Pseudo code: _PyTime_GetMonotonicClock() + timeout.