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gh-141004: Document unstable perf map functions in `ceval.h` by Yashp002 · Pull Request #143492 · python/cpython · GitHub

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gh-141004: Document unstable perf map functions in ceval.h #143492

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Merged
ZeroIntensity merged 8 commits into from
Jun 3, 2026
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gh-141004: Document unstable perf map functions in ceval.h #143492

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9a85c56
first commit perfmaps
Yashp002 Jan 6, 2026
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fix 1 perfmaps
Yashp002 Jan 6, 2026
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fix 2 perfmaps
Yashp002 Jan 8, 2026
e5a2111
perfmaps fix 3
Yashp002 Jan 31, 2026
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Merge branch 'main' into doc-ceval-perf
Yashp002 Jan 31, 2026
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fix capi_ignored
Yashp002 Jan 31, 2026
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perfmaps fix 4
Yashp002 Feb 2, 2026
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Merge branch 'main' into doc-ceval-perf
ZeroIntensity Jun 3, 2026
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40 changes: 40 additions & 0 deletions Doc/c-api/perfmaps.rst
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Expand Up @@ -49,3 +49,43 @@ Note that holding an :term:`attached thread state` is not required for these API
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.

.. c:function:: int PyUnstable_CopyPerfMapFile(const char *parent_filename)

Open the ``/tmp/perf-$pid.map`` file and append the content of *parent_filename*

StanFromIreland Jan 6, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

This should note what happens on Windows where this obviously won't work.

encukou Jan 7, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

That's the case for all of these functions; the info should be in the beginning of the section.

This doesn't open the perf map file directly; it should use the same wording as PyUnstable_WritePerfMapEntry: “Will call :c:func:PyUnstable_PerfMapState_Init…”

Yashp002 Jan 7, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

@encukou Would this wording be suitable then as a replacement for line 56 as:

"Calls :c:func:PyUnstable_PerfMapState_Init if the perf map is not yet
initialized, then append the content of parent_filename to the perf map."

Yashp002 Jan 8, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

@encukou or @StanFromIreland Could you verify this one too?

encukou Jan 8, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I'd say only “Append contents of the file named parent_filename to the perf map.” in the opening paragraph, and add the note about _Init later (like in WritePerfMapEntry docs).
to it.

This function is available on all platforms but only generates output on platforms
that support perf maps (currently only Linux). On other platforms, it does nothing.

.. versionadded:: 3.13

.. c:function:: int PyUnstable_PerfTrampoline_CompileCode(PyCodeObject *code)

Compile the given code object using the current perf trampoline.
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The "current" trampoline is the one set by the runtime or the most recent
:c:func:`PyUnstable_PerfTrampoline_SetPersistAfterFork` call.

If no trampoline is set, falls back to normal compilation (no perf map entry).

:param code: The code object to compile.
:return: 0 on success, -1 on failure.

.. versionadded:: 3.13

.. c:function:: int PyUnstable_PerfTrampoline_SetPersistAfterFork(int enable)

Set whether the perf trampoline should persist after a fork.
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* If ``enable`` is true (non-zero): perf map file remains open/valid post-fork.
Child process inherits all existing perf map entries.
* If ``enable`` is false (zero): perf map closes post-fork.
Child process gets empty perf map.

Default: false (clears on fork).

:param enable: 1 to enable, 0 to disable.
:return: 0 on success, -1 on failure.

.. versionadded:: 3.13
4 changes: 0 additions & 4 deletions Tools/check-c-api-docs/ignored_c_api.txt
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Expand Up @@ -43,10 +43,6 @@ PyDescr_TYPE
PyWrapperFlag_KEYWORDS
# cpython/fileobject.h
Py_UniversalNewlineFgets
# cpython/ceval.h
PyUnstable_CopyPerfMapFile
PyUnstable_PerfTrampoline_CompileCode
PyUnstable_PerfTrampoline_SetPersistAfterFork
# cpython/pyframe.h
PyUnstable_EXECUTABLE_KINDS
PyUnstable_EXECUTABLE_KIND_BUILTIN_FUNCTION
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