https://github.com/python/cpython/commit/eb892868b31322d7cf271bc25923e14b1f67ae38
commit: eb892868b31322d7cf271bc25923e14b1f67ae38
branch: main
author: Kevin Wang <[email protected]>
committer: colesbury <[email protected]>
date: 2025-12-01T19:04:47-05:00
summary:
gh-142048: Fix quadratically increasing GC delays (gh-142051)
The GC for the free threaded build would get slower with each collection due
to effectively double counting objects freed by the GC.
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2025-12-01-20-41-26.gh-issue-142048.c2YosX.rst
M Python/gc_free_threading.c
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2025-12-01-20-41-26.gh-issue-142048.c2YosX.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2025-12-01-20-41-26.gh-issue-142048.c2YosX.rst
new file mode 100644
index 00000000000000..1400dae13ffe32
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2025-12-01-20-41-26.gh-issue-142048.c2YosX.rst
@@ -0,0 +1,2 @@
+Fix quadratically increasing garbage collection delays in free-threaded
+build.
diff --git a/Python/gc_free_threading.c b/Python/gc_free_threading.c
index 1717603b947f90..e672e870db2f27 100644
--- a/Python/gc_free_threading.c
+++ b/Python/gc_free_threading.c
@@ -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;
}
}
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