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gh-143057: Use atomics for _PyRuntime.tracemalloc.config.tracing by Yhg1s · Pull Request #143066 · python/cpython · GitHub

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gh-143057: Use atomics for _PyRuntime.tracemalloc.config.tracing #143066

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Yhg1s wants to merge 1 commit into from
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gh-143057: Use atomics for _PyRuntime.tracemalloc.config.tracing #143066

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3 changes: 1 addition & 2 deletions Include/internal/pycore_tracemalloc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -20,8 +20,7 @@ struct _PyTraceMalloc_Config {
TRACEMALLOC_FINALIZED
} initialized;

/* Is tracemalloc tracing memory allocations?
Variable protected by the TABLES_LOCK(). */
/* Is tracemalloc tracing memory allocations? (Atomic.) */
int tracing;

/* limit of the number of frames in a traceback, 1 by default.
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19 changes: 15 additions & 4 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_release(&tracemalloc_config.tracing, 1);

kumaraditya303 Dec 22, 2025

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I think release is stronger than necessary because there are no data dependencies. The actual functions are called with the lock held anyways so only atomicity of tracing matters.

Yhg1s Dec 22, 2025

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I think there is a hidden data dependency: we don't want tracing to be enabled, an allocation to be tracked, and then another thread deallocating that tracked data without untracking.
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_release(&tracemalloc_config.tracing, 0);

/* unregister the hook on memory allocators */
PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &allocators.raw);
Expand Down Expand Up @@ -1207,6 +1207,12 @@ int
PyTraceMalloc_Track(unsigned int domain, uintptr_t ptr,
size_t size)
{
if (!_Py_atomic_load_int_relaxed(&tracemalloc_config.tracing)) {
// Exit early without attempting to lock if it doesn't look like
// we're tracing.
return -2;
}

PyGILState_STATE gil_state = PyGILState_Ensure();
TABLES_LOCK();

Expand All @@ -1215,7 +1221,7 @@ PyTraceMalloc_Track(unsigned int domain, uintptr_t ptr,
result = tracemalloc_add_trace_unlocked(domain, ptr, size);
}
else {
/* tracemalloc is not tracing: do nothing */
/* tracemalloc was disabled before we locked tables; do nothing. */
result = -2;
}

Expand All @@ -1228,6 +1234,11 @@ PyTraceMalloc_Track(unsigned int domain, uintptr_t ptr,
int
PyTraceMalloc_Untrack(unsigned int domain, uintptr_t ptr)
{
if (!_Py_atomic_load_int_relaxed(&tracemalloc_config.tracing)) {
// Exit early without attempting to lock if it doesn't look like
// we're tracing.
return -2;
}
TABLES_LOCK();

int result;
Expand All @@ -1236,7 +1247,7 @@ PyTraceMalloc_Untrack(unsigned int domain, uintptr_t ptr)
result = 0;
}
else {
/* tracemalloc is not tracing: do nothing */
/* tracemalloc was disabled before we locked tables; do nothing. */
result = -2;
}

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