1 files changed, 47 insertions, 43 deletions

diff --git a/Modules/_xxsubinterpretersmodule.c b/Modules/_xxsubinterpretersmodule.c
index 5d4f1b9..c0958c6 100644
--- a/Modules/_xxsubinterpretersmodule.c
+++ b/Modules/_xxsubinterpretersmodule.c
@@ -2,7 +2,14 @@
 /* interpreters module */
 /* low-level access to interpreter primitives */
 
+#ifndef Py_BUILD_CORE_BUILTIN
+#  define Py_BUILD_CORE_MODULE 1
+#endif
+
 #include "Python.h"
+#include "pycore_initconfig.h"    // _PyErr_SetFromPyStatus()
+#include "pycore_pyerrors.h"      // _PyErr_ChainExceptions1()
+#include "pycore_pystate.h"       // _PyInterpreterState_SetRunningMain()
 #include "interpreteridobject.h"
 
 
@@ -353,41 +360,14 @@ exceptions_init(PyObject *mod)
 }
 
 static int
-_is_running(PyInterpreterState *interp)
-{
-    PyThreadState *tstate = PyInterpreterState_ThreadHead(interp);
-    if (PyThreadState_Next(tstate) != NULL) {
-        PyErr_SetString(PyExc_RuntimeError,
-                        "interpreter has more than one thread");
-        return -1;
-    }
-
-    assert(!PyErr_Occurred());
-    struct _PyInterpreterFrame *frame = tstate->cframe->current_frame;
-    if (frame == NULL) {
-        return 0;
-    }
-    return 1;
-}
-
-static int
-_ensure_not_running(PyInterpreterState *interp)
+_run_script(PyInterpreterState *interp, const char *codestr,
+            _sharedns *shared, _sharedexception *sharedexc)
 {
-    int is_running = _is_running(interp);
-    if (is_running < 0) {
+    if (_PyInterpreterState_SetRunningMain(interp) < 0) {
+        // We skip going through the shared exception.
         return -1;
     }
-    if (is_running) {
-        PyErr_Format(PyExc_RuntimeError, "interpreter already running");
-        return -1;
-    }
-    return 0;
-}
 
-static int
-_run_script(PyInterpreterState *interp, const char *codestr,
-            _sharedns *shared, _sharedexception *sharedexc)
-{
     PyObject *excval = NULL;
     PyObject *main_mod = _PyInterpreterState_GetMainModule(interp);
     if (main_mod == NULL) {
@@ -417,6 +397,7 @@ _run_script(PyInterpreterState *interp, const char *codestr,
     else {
         Py_DECREF(result);  // We throw away the result.
     }
+    _PyInterpreterState_SetNotRunningMain(interp);
 
     *sharedexc = no_exception;
     return 0;
@@ -432,6 +413,7 @@ error:
     }
     Py_XDECREF(excval);
     assert(!PyErr_Occurred());
+    _PyInterpreterState_SetNotRunningMain(interp);
     return -1;
 }
 
@@ -439,9 +421,6 @@ static int
 _run_script_in_interpreter(PyObject *mod, PyInterpreterState *interp,
                            const char *codestr, PyObject *shareables)
 {
-    if (_ensure_not_running(interp) < 0) {
-        return -1;
-    }
     module_state *state = get_module_state(mod);
 
     _sharedns *shared = _get_shared_ns(shareables);
@@ -452,8 +431,26 @@ _run_script_in_interpreter(PyObject *mod, PyInterpreterState *interp,
     // Switch to interpreter.
     PyThreadState *save_tstate = NULL;
     if (interp != PyInterpreterState_Get()) {
-        // XXX Using the "head" thread isn't strictly correct.
+        // XXX gh-109860: Using the "head" thread isn't strictly correct.
         PyThreadState *tstate = PyInterpreterState_ThreadHead(interp);
+        assert(tstate != NULL);
+        // Hack (until gh-109860): The interpreter's initial thread state
+        // is least likely to break.
+        while(tstate->next != NULL) {
+            tstate = tstate->next;
+        }
+        // We must do this check before switching interpreters, so any
+        // exception gets raised in the right one.
+        // XXX gh-109860: Drop this redundant check once we stop
+        // re-using tstates that might already be in use.
+        if (_PyInterpreterState_IsRunningMain(interp)) {
+            PyErr_SetString(PyExc_RuntimeError,
+                            "interpreter already running");
+            if (shared != NULL) {
+                _sharedns_free(shared);
+            }
+            return -1;
+        }
         // XXX Possible GILState issues?
         save_tstate = PyThreadState_Swap(tstate);
     }
@@ -473,8 +470,10 @@ _run_script_in_interpreter(PyObject *mod, PyInterpreterState *interp,
         _sharedexception_apply(&exc, state->RunFailedError);
     }
     else if (result != 0) {
-        // We were unable to allocate a shared exception.
-        PyErr_NoMemory();
+        if (!PyErr_Occurred()) {
+            // We were unable to allocate a shared exception.
+            PyErr_NoMemory();
+        }
     }
 
     if (shared != NULL) {
@@ -569,12 +568,20 @@ interp_destroy(PyObject *self, PyObject *args, PyObject *kwds)
     // Ensure the interpreter isn't running.
     /* XXX We *could* support destroying a running interpreter but
        aren't going to worry about it for now. */
-    if (_ensure_not_running(interp) < 0) {
+    if (_PyInterpreterState_IsRunningMain(interp)) {
+        PyErr_Format(PyExc_RuntimeError, "interpreter running");
         return NULL;
     }
 
     // Destroy the interpreter.
+    // XXX gh-109860: Using the "head" thread isn't strictly correct.
     PyThreadState *tstate = PyInterpreterState_ThreadHead(interp);
+    assert(tstate != NULL);
+    // Hack (until gh-109860): The interpreter's initial thread state
+    // is least likely to break.
+    while(tstate->next != NULL) {
+        tstate = tstate->next;
+    }
     // XXX Possible GILState issues?
     PyThreadState *save_tstate = PyThreadState_Swap(tstate);
     Py_EndInterpreter(tstate);
@@ -743,11 +750,7 @@ interp_is_running(PyObject *self, PyObject *args, PyObject *kwds)
     if (interp == NULL) {
         return NULL;
     }
-    int is_running = _is_running(interp);
-    if (is_running < 0) {
-        return NULL;
-    }
-    if (is_running) {
+    if (_PyInterpreterState_IsRunningMain(interp)) {
         Py_RETURN_TRUE;
     }
     Py_RETURN_FALSE;
@@ -758,6 +761,7 @@ PyDoc_STRVAR(is_running_doc,
 \n\
 Return whether or not the identified interpreter is running.");
 
+
 static PyMethodDef module_functions[] = {
     {"create",                    _PyCFunction_CAST(interp_create),
      METH_VARARGS | METH_KEYWORDS, create_doc},