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gh-143057: avoid lock in tracemalloc APIs when it is not enabled #143065

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Merged
kumaraditya303 merged 4 commits into from
Dec 22, 2025
Merged

gh-143057: avoid lock in tracemalloc APIs when it is not enabled #143065

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0e94835
avoid lock in tracemalloc in general case
kumaraditya303 Dec 22, 2025
19f6c87
code review
kumaraditya303 Dec 22, 2025
c4e9ed0
📜🤖 Added by blurb_it.
blurb-it[bot] Dec 22, 2025
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Update Misc/NEWS.d/next/Core_and_Builtins/2025-12-22-12-03-09.gh-issu…
kumaraditya303 Dec 22, 2025
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avoid lock in tracemalloc in general case
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@kumaraditya303
kumaraditya303 committed Dec 22, 2025
commit 0e9483510468714042f9164dba8a824b0c2c72c2
5 changes: 4 additions & 1 deletion Include/internal/pycore_tracemalloc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -21,7 +21,10 @@ struct _PyTraceMalloc_Config {
} initialized;

/* Is tracemalloc tracing memory allocations?
Variable protected by the TABLES_LOCK(). */
Variable protected by the TABLES_LOCK() and stored atomically.
Atomic store is used so that it can read without locking for the
general case of checking if tracemalloc is enabled.
*/
int tracing;

/* limit of the number of frames in a traceback, 1 by default.
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43 changes: 23 additions & 20 deletions Python/tracemalloc.c
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Expand Up @@ -850,7 +850,7 @@ _PyTraceMalloc_Start(int max_nframe)

/* everything is ready: start tracing Python memory allocations */
TABLES_LOCK();
tracemalloc_config.tracing = 1;
_Py_atomic_store_int_relaxed(&tracemalloc_config.tracing, 1);
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TABLES_UNLOCK();

return 0;
Expand All @@ -867,7 +867,7 @@ _PyTraceMalloc_Stop(void)
}

/* stop tracing Python memory allocations */
tracemalloc_config.tracing = 0;
_Py_atomic_store_int_relaxed(&tracemalloc_config.tracing, 0);

/* unregister the hook on memory allocators */
PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &allocators.raw);
Expand Down Expand Up @@ -1207,18 +1207,20 @@ int
PyTraceMalloc_Track(unsigned int domain, uintptr_t ptr,
size_t size)
{
if (_Py_atomic_load_int_relaxed(&tracemalloc_config.tracing) == 0) {
/* tracemalloc is not tracing: do nothing */
return -2;
}
PyGILState_STATE gil_state = PyGILState_Ensure();
TABLES_LOCK();

int result;
if (tracemalloc_config.tracing) {
result = tracemalloc_add_trace_unlocked(domain, ptr, size);
}
else {
// Check again now that we hold the lock
if (!tracemalloc_config.tracing) {
TABLES_UNLOCK();
PyGILState_Release(gil_state);
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/* tracemalloc is not tracing: do nothing */
result = -2;
return -2;
}

int result = tracemalloc_add_trace_unlocked(domain, ptr, size);
TABLES_UNLOCK();
PyGILState_Release(gil_state);
return result;
Expand All @@ -1228,20 +1230,21 @@ PyTraceMalloc_Track(unsigned int domain, uintptr_t ptr,
int
PyTraceMalloc_Untrack(unsigned int domain, uintptr_t ptr)
{
TABLES_LOCK();

int result;
if (tracemalloc_config.tracing) {
tracemalloc_remove_trace_unlocked(domain, ptr);
result = 0;
}
else {
if (_Py_atomic_load_int_relaxed(&tracemalloc_config.tracing) == 0) {
/* tracemalloc is not tracing: do nothing */
result = -2;
return -2;
}

TABLES_LOCK();
// Check again now that we hold the lock
if (!tracemalloc_config.tracing) {
TABLES_UNLOCK();
/* tracemalloc is not tracing: do nothing */
return -2;
}
tracemalloc_remove_trace_unlocked(domain, ptr);
TABLES_UNLOCK();
return result;
return 0;
}


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