bpo-40453: Add PyConfig._isolated_subinterpreter (GH-19820)

An isolated subinterpreter cannot spawn threads, spawn a child
process or call os.fork().

* Add private _Py_NewInterpreter(isolated_subinterpreter) function.
* Add isolated=True keyword-only parameter to
  _xxsubinterpreters.create().
* Allow again os.fork() in "non-isolated" subinterpreters.

1 files changed, 8 insertions, 0 deletions

diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
index b3d90b2..77baba4 100644
--- a/Modules/_threadmodule.c
+++ b/Modules/_threadmodule.c
@@ -1085,6 +1085,14 @@ thread_PyThread_start_new_thread(PyObject *self, PyObject *fargs)
                         "optional 3rd arg must be a dictionary");
         return NULL;
     }
+
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    if (interp->config._isolated_interpreter) {
+        PyErr_SetString(PyExc_RuntimeError,
+                        "thread is not supported for isolated subinterpreters");
+        return NULL;
+    }
+
     boot = PyMem_NEW(struct bootstate, 1);
     if (boot == NULL)
         return PyErr_NoMemory();