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gh-142048: Fix quadratically increasing GC delays (gh-142051)

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The GC for the free threaded build would get slower with each collection due
to effectively double counting objects freed by the GC.
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Kevin Wang 2025-12-01 19:04:47 -05:00 • committed by GitHub
parent e32c975640
commit eb892868b3
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Misc/NEWS.d/next/Core_and_Builtins/2025-12-01-20-41-26.gh-issue-142048.c2YosX.rst Normal file
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@ -0,0 +1,2 @@
Fix quadratically increasing garbage collection delays in free-threaded
build.

14
Python/gc_free_threading.c
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@ -2210,7 +2210,19 @@ record_deallocation(PyThreadState *tstate)
gc->alloc_count--;
if (gc->alloc_count <= -LOCAL_ALLOC_COUNT_THRESHOLD) {
GCState *gcstate = &tstate->interp->gc;
_Py_atomic_add_int(&gcstate->young.count, (int)gc->alloc_count);
int count = _Py_atomic_load_int_relaxed(&gcstate->young.count);
int new_count;
do {
if (count == 0) {
break;
}
new_count = count + (int)gc->alloc_count;
if (new_count < 0) {
new_count = 0;
}
} while (!_Py_atomic_compare_exchange_int(&gcstate->young.count,
&count,
new_count));
gc->alloc_count = 0;
}
}