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gh-143057: Use atomics for _PyRuntime.tracemalloc.config.tracing - #143066
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early in `PyTraceMalloc_Track` and `PyTraceMalloc_Untrack` if tracemalloc isn't enabled. This avoids a significant scaling issue when tracemalloc isn't enabled, in extension modules that properly use the PyTraceMalloc_Track API (like numpy).
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Python/tracemalloc.c
| /* everything is ready: start tracing Python memory allocations */ | ||
| TABLES_LOCK(); | ||
| tracemalloc_config.tracing = 1; | ||
| _Py_atomic_store_int_release(&tracemalloc_config.tracing, 1); |
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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.
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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.
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Use atomics for the _PyRuntime.tracemalloc.config.tracing so we can bail early in PyTraceMalloc_Track and PyTraceMalloc_Untrack if tracemalloc isn't enabled. This avoids a significant scaling issue when tracemalloc isn't enabled, in extension modules that properly use the PyTraceMalloc_Track API (like numpy).