bpo-42208: Call GC collect earlier in PyInterpreterState_Clear() (GH-23044)

The last GC collection is now done before clearing builtins and sys
dictionaries. Add also assertions to ensure that gc.collect() is no
longer called after _PyGC_Fini().

Pass also the tstate to PyInterpreterState_Clear() to pass the
correct tstate to _PyGC_CollectNoFail() and _PyGC_Fini().

2 files changed, 28 insertions, 11 deletions

diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index adef161..ff58c1b 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -1576,10 +1576,7 @@ finalize_interp_clear(PyThreadState *tstate)
     int is_main_interp = _Py_IsMainInterpreter(tstate);
 
     /* Clear interpreter state and all thread states */
-    PyInterpreterState_Clear(tstate->interp);
-
-    /* Last explicit GC collection */
-    _PyGC_CollectNoFail(tstate);
+    _PyInterpreterState_Clear(tstate);
 
     /* Clear all loghooks */
     /* Both _PySys_Audit function and users still need PyObject, such as tuple.
@@ -1588,8 +1585,6 @@ finalize_interp_clear(PyThreadState *tstate)
         _PySys_ClearAuditHooks(tstate);
     }
 
-    _PyGC_Fini(tstate);
-
     if (is_main_interp) {
         _Py_HashRandomization_Fini();
         _PyArg_Fini();
diff --git a/Python/pystate.c b/Python/pystate.c
index eb24f2b..e888986 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -268,14 +268,11 @@ out_of_memory:
 }
 
 
-void
-PyInterpreterState_Clear(PyInterpreterState *interp)
+static void
+interpreter_clear(PyInterpreterState *interp, PyThreadState *tstate)
 {
     _PyRuntimeState *runtime = interp->runtime;
 
-    /* Use the current Python thread state to call audit hooks,
-       not the current Python thread state of 'interp'. */
-    PyThreadState *tstate = _PyThreadState_GET();
     if (_PySys_Audit(tstate, "cpython.PyInterpreterState_Clear", NULL) < 0) {
         _PyErr_Clear(tstate);
     }
@@ -306,6 +303,12 @@ PyInterpreterState_Clear(PyInterpreterState *interp)
     if (_PyRuntimeState_GetFinalizing(runtime) == NULL) {
         _PyWarnings_Fini(interp);
     }
+
+    /* Last garbage collection on this interpreter */
+    _PyGC_CollectNoFail(tstate);
+
+    _PyGC_Fini(tstate);
+
     /* We don't clear sysdict and builtins until the end of this function.
        Because clearing other attributes can execute arbitrary Python code
        which requires sysdict and builtins. */
@@ -320,6 +323,25 @@ PyInterpreterState_Clear(PyInterpreterState *interp)
 }
 
 
+void
+PyInterpreterState_Clear(PyInterpreterState *interp)
+{
+    // Use the current Python thread state to call audit hooks and to collect
+    // garbage. It can be different than the current Python thread state
+    // of 'interp'.
+    PyThreadState *current_tstate = _PyThreadState_GET();
+
+    interpreter_clear(interp, current_tstate);
+}
+
+
+void
+_PyInterpreterState_Clear(PyThreadState *tstate)
+{
+    interpreter_clear(tstate->interp, tstate);
+}
+
+
 static void
 zapthreads(PyInterpreterState *interp, int check_current)
 {