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, 10 insertions, 3 deletions

diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 7909cdbf5b..5726a559cf 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -1526,7 +1526,7 @@ Py_Finalize(void)
 */
 
 static PyStatus
-new_interpreter(PyThreadState **tstate_p)
+new_interpreter(PyThreadState **tstate_p, int isolated_subinterpreter)
 {
     PyStatus status;
 
@@ -1573,6 +1573,7 @@ new_interpreter(PyThreadState **tstate_p)
     if (_PyStatus_EXCEPTION(status)) {
         goto error;
     }
+    interp->config._isolated_interpreter = isolated_subinterpreter;
 
     status = pycore_interp_init(tstate);
     if (_PyStatus_EXCEPTION(status)) {
@@ -1606,10 +1607,10 @@ error:
 }
 
 PyThreadState *
-Py_NewInterpreter(void)
+_Py_NewInterpreter(int isolated_subinterpreter)
 {
     PyThreadState *tstate = NULL;
-    PyStatus status = new_interpreter(&tstate);
+    PyStatus status = new_interpreter(&tstate, isolated_subinterpreter);
     if (_PyStatus_EXCEPTION(status)) {
         Py_ExitStatusException(status);
     }
@@ -1617,6 +1618,12 @@ Py_NewInterpreter(void)
 
 }
 
+PyThreadState *
+Py_NewInterpreter(void)
+{
+    return _Py_NewInterpreter(0);
+}
+
 /* Delete an interpreter and its last thread.  This requires that the
    given thread state is current, that the thread has no remaining
    frames, and that it is its interpreter's only remaining thread.