gh-98610: Adjust the Optional Restrictions on Subinterpreters (GH-98618)

Previously, the optional restrictions on subinterpreters were: disallow fork, subprocess, and threads.  By default, we were disallowing all three for "isolated" interpreters.  We always allowed all three for the main interpreter and those created through the legacy `Py_NewInterpreter()` API.

Those settings were a bit conservative, so here we've adjusted the optional restrictions to: fork, exec, threads, and daemon threads.  The default for "isolated" interpreters disables fork, exec, and daemon threads.  Regular threads are allowed by default.  We continue always allowing everything For the main interpreter and the legacy API.

In the code, we add `_PyInterpreterConfig.allow_exec` and  `_PyInterpreterConfig.allow_daemon_threads`.  We also add `Py_RTFLAGS_DAEMON_THREADS` and `Py_RTFLAGS_EXEC`.

1 files changed, 8 insertions, 2 deletions

diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index d26ae74..e648492 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -615,15 +615,21 @@ static void
 init_interp_settings(PyInterpreterState *interp, const _PyInterpreterConfig *config)
 {
     assert(interp->feature_flags == 0);
+
     if (config->allow_fork) {
         interp->feature_flags |= Py_RTFLAGS_FORK;
     }
-    if (config->allow_subprocess) {
-        interp->feature_flags |= Py_RTFLAGS_SUBPROCESS;
+    if (config->allow_exec) {
+        interp->feature_flags |= Py_RTFLAGS_EXEC;
     }
+    // Note that fork+exec is always allowed.
+
     if (config->allow_threads) {
         interp->feature_flags |= Py_RTFLAGS_THREADS;
     }
+    if (config->allow_daemon_threads) {
+        interp->feature_flags |= Py_RTFLAGS_DAEMON_THREADS;
+    }
 }