.. highlight:: c
.. _c-api-time:
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.
Raw Clock Functions
-------------------
Similar to clock functions, but don't set an exception on error and don't
require the caller to hold the GIL.
On success, the functions return ``0``.
On failure, they set ``*result`` to ``0`` and return ``-1``, *without* setting
an exception. To get the cause of the error, acquire the GIL and call the
regular (non-``Raw``) function. Note that the regular function may succeed after
the ``Raw`` one failed.
.. c:function:: int PyTime_MonotonicRaw(PyTime_t *result)
Similar to :c:func:`PyTime_Monotonic`,
but don't set an exception on error and don't require holding the GIL.
.. c:function:: int PyTime_PerfCounterRaw(PyTime_t *result)
Similar to :c:func:`PyTime_PerfCounter`,
but don't set an exception on error and don't require holding the GIL.
.. c:function:: int PyTime_TimeRaw(PyTime_t *result)
Similar to :c:func:`PyTime_Time`,
but don't set an exception on error and don't require holding the GIL.
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.
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