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gh-161242: Add a freelist for traceback objects #161243

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Merged
eendebakpt merged 4 commits into from
Nov 6, 2026
+12 −7
Merged

gh-161242: Add a freelist for traceback objects #161243

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0251311
Add a freelist for traceback objects
eendebakpt Nov 3, 2026
6765b38
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eendebakpt Nov 3, 2026
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eendebakpt Nov 6, 2026
81dd418
Merge branch 'main' into traceback_freelist_only
eendebakpt Nov 6, 2026
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2 changes: 2 additions & 0 deletions Include/internal/pycore_freelist_state.h
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,7 @@ extern "C" {
# define Py_pycfunctionobject_MAXFREELIST 16
# define Py_pycmethodobject_MAXFREELIST 16
# define Py_pymethodobjects_MAXFREELIST 20
# define Py_tracebacks_MAXFREELIST 8

// A generic freelist of either PyObjects or other data structures.
struct _Py_freelist {
Expand Down Expand Up @@ -66,6 +67,7 @@ struct _Py_freelists {
struct _Py_freelist pycfunctionobject;
struct _Py_freelist pycmethodobject;
struct _Py_freelist pymethodobjects;
struct _Py_freelist tracebacks;
};

#ifdef __cplusplus
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1 change: 1 addition & 0 deletions Objects/object.c
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Expand Up @@ -956,6 +956,7 @@ _PyObject_ClearFreeLists(struct _Py_freelists *freelists, int is_finalization)
clear_freelist(&freelists->pycfunctionobject, is_finalization, PyObject_GC_Del);
clear_freelist(&freelists->pycmethodobject, is_finalization, PyObject_GC_Del);
clear_freelist(&freelists->pymethodobjects, is_finalization, free_object);
clear_freelist(&freelists->tracebacks, is_finalization, PyObject_GC_Del);
}

/*
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16 changes: 9 additions & 7 deletions Python/traceback.c
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Expand Up @@ -4,6 +4,7 @@
#include "Python.h"
#include "pycore_call.h" // _PyObject_CallMethod()
#include "pycore_fileutils.h" // _Py_BEGIN_SUPPRESS_IPH
#include "pycore_freelist.h" // _Py_FREELIST_POP()
#include "pycore_frame.h" // PyFrameObject
#include "pycore_interp.h" // PyInterpreterState.gc
#include "pycore_interpframe.h" // _PyFrame_GetCode()
Expand Down Expand Up @@ -79,15 +80,16 @@ tb_create_raw(PyTracebackObject *next, PyFrameObject *frame, int lasti,
int lineno)
{
PyTracebackObject *tb;
if ((next != NULL && !PyTraceBack_Check(next)) ||
frame == NULL || !PyFrame_Check(frame)) {
PyErr_BadInternalCall();

@sobolevn sobolevn Nov 3, 2026

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Is it safe to remove this call? tb_create_raw is used in several C-API calls that can in theory reach this point.

@eendebakpt eendebakpt Nov 3, 2026

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All callers have their own guards: tb_new_impl is checked via AC, _PyTraceBack_FromFrame checks with asserts as well (callers of _PyTraceBack_FromFrame do perform actual checks, _PyTraceBack_FromFrame is internal api). Maybe I missed a path?

return NULL;
assert(next == NULL || PyTraceBack_Check(next));
assert(frame != NULL);
assert(PyFrame_Check(frame));
tb = _Py_FREELIST_POP(PyTracebackObject, tracebacks);
if (tb == NULL) {
tb = PyObject_GC_New(PyTracebackObject, &PyTraceBack_Type);
}
tb = PyObject_GC_New(PyTracebackObject, &PyTraceBack_Type);
if (tb != NULL) {
tb->tb_next = (PyTracebackObject*)Py_XNewRef(next);
tb->tb_frame = (PyFrameObject*)Py_XNewRef(frame);
tb->tb_frame = (PyFrameObject*)Py_NewRef(frame);
tb->tb_lasti = lasti;
tb->tb_lineno = lineno;
PyObject_GC_Track(tb);
Expand Down Expand Up @@ -237,7 +239,7 @@ tb_dealloc(PyObject *op)
PyObject_GC_UnTrack(tb);
Py_XDECREF(tb->tb_next);
Py_XDECREF(tb->tb_frame);
PyObject_GC_Del(tb);
_Py_FREELIST_FREE(tracebacks, tb, PyObject_GC_Del);
}

static int
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