[3.12] gh-105716: Support Background Threads in Subinterpreters Consistently (gh-109921) (gh-110707)

The existence of background threads running on a subinterpreter was preventing interpreters from getting properly destroyed, as well as impacting the ability to run the interpreter again. It also affected how we wait for non-daemon threads to finish.

We add PyInterpreterState.threads.main, with some internal C-API functions.

(cherry-picked from commit 1dd9dee45d2591b4e701039d1673282380696849)

1 files changed, 37 insertions, 0 deletions

diff --git a/Python/pystate.c b/Python/pystate.c
index 0430454..534e77f 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -1049,6 +1049,39 @@ _PyInterpreterState_DeleteExceptMain(_PyRuntimeState *runtime)
 #endif
 
 
+int
+_PyInterpreterState_SetRunningMain(PyInterpreterState *interp)
+{
+    if (interp->threads_main != NULL) {
+        PyErr_SetString(PyExc_RuntimeError,
+                        "interpreter already running");
+        return -1;
+    }
+    PyThreadState *tstate = current_fast_get(&_PyRuntime);
+    _Py_EnsureTstateNotNULL(tstate);
+    if (tstate->interp != interp) {
+        PyErr_SetString(PyExc_RuntimeError,
+                        "current tstate has wrong interpreter");
+        return -1;
+    }
+    interp->threads_main = tstate;
+    return 0;
+}
+
+void
+_PyInterpreterState_SetNotRunningMain(PyInterpreterState *interp)
+{
+    assert(interp->threads_main == current_fast_get(&_PyRuntime));
+    interp->threads_main = NULL;
+}
+
+int
+_PyInterpreterState_IsRunningMain(PyInterpreterState *interp)
+{
+    return (interp->threads_main != NULL);
+}
+
+
 //----------
 // accessors
 //----------
@@ -2757,6 +2790,10 @@ _register_builtins_for_crossinterpreter_data(struct _xidregistry *xidregistry)
 }
 
 
+/*************/
+/* Other API */
+/*************/
+
 _PyFrameEvalFunction
 _PyInterpreterState_GetEvalFrameFunc(PyInterpreterState *interp)
 {