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.. highlight:: c
.. _perfmaps:
Support for Perf Maps
----------------------
On supported platforms (as of this writing, only Linux), the runtime can take
advantage of *perf map files* to make Python functions visible to an external
profiling tool (such as `perf <https://perf.wiki.kernel.org/index.php/Main_Page>`_).
A running process may create a file in the ``/tmp`` directory, which contains entries
that can map a section of executable code to a name. This interface is described in the
`documentation of the Linux Perf tool <https://git.kernel.org/pub/scm/linux/
kernel/git/torvalds/linux.git/tree/tools/perf/Documentation/jit-interface.txt>`_.
In Python, these helper APIs can be used by libraries and features that rely
on generating machine code on the fly.
Note that holding an :term:`attached thread state` is not required for these APIs.
.. c:function:: int PyUnstable_PerfMapState_Init(void)
Open the ``/tmp/perf-$pid.map`` file, unless it's already opened, and create
a lock to ensure thread-safe writes to the file (provided the writes are
done through :c:func:`PyUnstable_WritePerfMapEntry`). Normally, there's no need
to call this explicitly; just use :c:func:`PyUnstable_WritePerfMapEntry`
and it will initialize the state on first call.
Returns ``0`` on success, ``-1`` on failure to create/open the perf map file,
or ``-2`` on failure to create a lock. Check ``errno`` for more information
about the cause of a failure.
.. c:function:: int PyUnstable_WritePerfMapEntry(const void *code_addr, unsigned int code_size, const char *entry_name)
Write one single entry to the ``/tmp/perf-$pid.map`` file. This function is
thread safe. Here is what an example entry looks like::
# address size name
7f3529fcf759 b py::bar:/run/t.py
Will call :c:func:`PyUnstable_PerfMapState_Init` before writing the entry, if
the perf map file is not already opened. Returns ``0`` on success, or the
same error codes as :c:func:`PyUnstable_PerfMapState_Init` on failure.
.. c:function:: void PyUnstable_PerfMapState_Fini(void)
Close the perf map file opened by :c:func:`PyUnstable_PerfMapState_Init`.
This is called by the runtime itself during interpreter shut-down. In
general, there shouldn't be a reason to explicitly call this, except to
handle specific scenarios such as forking.
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