Add news entry

Signed-off-by: Pablo Galindo <pablogsal@gmail.com>

Doc/whatsnew/3.12.rst

@@ -93,6 +93,13 @@ Other Language Changes
   when parsing source code containing null bytes. (Contributed by Pablo Galindo
   in :gh:`96670`.)
 
+* The Garbage Collector now runs only on the eval breaker mechanism of the
+  Python bytecode evaluation loop instead on object allocations. The GC can
+  also run when :c:func:`PyErr_CheckSignals` is called so C extensions that
+  need to run for a long time without executing any Python code also have a
+  chance to execute the GC periodically. (Contributed by Pablo Galindo in
+  :gh:`97922`.)
+
 New Modules
 ===========
 

Misc/NEWS.d/next/Core and Builtins/2022-10-05-11-37-15.gh-issue-97922.Zu9Bge.rst

@@ -0,0 +1,5 @@
+The Garbage Collector now runs only on the eval breaker mechanism of the
+Python bytecode evaluation loop instead on object allocations. The GC can
+also run when :c:func:`PyErr_CheckSignals` is called so C extensions that
+need to run for a long time without executing any Python code also have a
+chance to execute the GC periodically.

Modules/gcmodule.c

@@ -2255,9 +2255,15 @@ PyObject_IS_GC(PyObject *obj)
 void
 _Py_ScheduleGC(PyInterpreterState *interp)
 {
+    GCState *gcstate = &interp->gc;
+    if (gcstate->collecting == 1) {
+        return;
+    }
     struct _ceval_state *ceval = &interp->ceval;
-    _Py_atomic_store_relaxed(&ceval->gc_scheduled, 1);
-    _Py_atomic_store_relaxed(&ceval->eval_breaker, 1);
+    if (!_Py_atomic_load_relaxed(&ceval->gc_scheduled)) {
+        _Py_atomic_store_relaxed(&ceval->gc_scheduled, 1);
+        _Py_atomic_store_relaxed(&ceval->eval_breaker, 1);
+    }
 }
 
 void

Python/ceval_gil.c

@@ -70,7 +70,8 @@ COMPUTE_EVAL_BREAKER(PyInterpreterState *interp,
            && _Py_ThreadCanHandleSignals(interp))
         | (_Py_atomic_load_relaxed_int32(&ceval2->pending.calls_to_do)
            && _Py_ThreadCanHandlePendingCalls())
-        | ceval2->pending.async_exc);
+        | ceval2->pending.async_exc
+        | _Py_atomic_load_relaxed_int32(&ceval2->gc_scheduled));
 }
 
 
@@ -945,6 +946,7 @@ _Py_HandlePending(PyThreadState *tstate)
     if (_Py_atomic_load_relaxed_int32(&interp_ceval_state->gc_scheduled)) {
         _Py_atomic_store_relaxed(&interp_ceval_state->gc_scheduled, 0);
         _Py_RunGC(tstate);
+        COMPUTE_EVAL_BREAKER(tstate->interp, ceval, interp_ceval_state);
     }
 
     /* Pending signals */
@@ -988,16 +990,17 @@ _Py_HandlePending(PyThreadState *tstate)
         return -1;
     }
 
-#ifdef MS_WINDOWS
-    // bpo-42296: On Windows, _PyEval_SignalReceived() can be called in a
-    // different thread than the Python thread, in which case
+
+    // It is possible that some of the conditions that trigger the eval breaker
+    // are called in a different thread than the Python thread. An example of
+    // this is bpo-42296: On Windows, _PyEval_SignalReceived() can be called in
+    // a different thread than the Python thread, in which case
     // _Py_ThreadCanHandleSignals() is wrong. Recompute eval_breaker in the
     // current Python thread with the correct _Py_ThreadCanHandleSignals()
     // value. It prevents to interrupt the eval loop at every instruction if
     // the current Python thread cannot handle signals (if
     // _Py_ThreadCanHandleSignals() is false).
     COMPUTE_EVAL_BREAKER(tstate->interp, ceval, interp_ceval_state);
-#endif
 
     return 0;
 }