Fix failing builds.

Author: ZeroIntensity

Include/internal/pycore_interp.h

@@ -421,6 +421,9 @@ _PyInterpreterState_PreventMain(PyInterpreterState *interp);
 PyAPI_FUNC(int)
 _PyInterpreterState_IsRunningAllowed(PyInterpreterState *interp);
 
+PyAPI_FUNC(PyThreadState *)
+_PyInterpreterState_ThreadHeadSafe(PyInterpreterState *interp);
+
 #define RARE_EVENT_INTERP_INC(interp, name) \
     do { \
         /* saturating add */ \

Modules/_interpretersmodule.c

@@ -711,18 +711,17 @@ interp_destroy(PyObject *self, PyObject *args, PyObject *kwds)
         return NULL;
     }
 
-    HEAD_LOCK(&_PyRuntime);
-    if (interp->threads.head != NULL)
+    // It would be nice if we could just lock the runtime here, but
+    // unfortunately we don't have access to private PyMutex functions from this module.
+    if (_PyInterpreterState_ThreadHeadSafe(interp) != NULL)
     {
         /*
          * We're in a weird limbo where the main thread isn't set but
          * the thread states haven't fully cleared yet.
          */
-        HEAD_UNLOCK(&_PyRuntime);
         PyErr_SetString(PyExc_InterpreterError, "interpreter is still finishing");
         return NULL;
     }
-    HEAD_UNLOCK(&_PyRuntime);
 
     /*
      * Running main has now been prevented, the interpreter will

Python/pystate.c

@@ -2557,6 +2557,16 @@ PyThreadState_Next(PyThreadState *tstate) {
 }
 
 
+PyThreadState *
+_PyInterpreterState_ThreadHeadSafe(PyInterpreterState *interp)
+{
+    HEAD_LOCK(&_PyRuntime);
+    PyThreadState *tstate = interp->threads.head;
+    HEAD_UNLOCK(&_PyRuntime);
+    return tstate;
+}
+
+
 /********************************************/
 /* reporting execution state of all threads */
 /********************************************/