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gh-112529: Make the GC scheduling thread-safe (#114880)

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The GC keeps track of the number of allocations (less deallocations)
since the last GC. This buffers the count in thread-local state and uses
atomic operations to modify the per-interpreter count. The thread-local
buffering avoids contention on shared state.

A consequence is that the GC scheduling is not as precise, so
"test_sneaky_frame_object" is skipped because it requires that the GC be
run exactly after allocating a frame object.
This commit is contained in:
Sam Gross 2024-02-16 11:22:27 -05:00 • committed by GitHub
parent f92857a930
commit b24c9161a6
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7 changed files with 71 additions and 16 deletions
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10
Modules/gcmodule.c
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@ -201,6 +201,16 @@ gc_get_count_impl(PyObject *module)
/*[clinic end generated code: output=354012e67b16398f input=a392794a08251751]*/
{
GCState *gcstate = get_gc_state();
#ifdef Py_GIL_DISABLED
_PyThreadStateImpl *tstate = (_PyThreadStateImpl *)_PyThreadState_GET();
struct _gc_thread_state *gc = &tstate->gc;
// Flush the local allocation count to the global count
_Py_atomic_add_int(&gcstate->generations[0].count, (int)gc->alloc_count);
gc->alloc_count = 0;
#endif
return Py_BuildValue("(iii)",
gcstate->generations[0].count,
gcstate->generations[1].count,