gh-109746: Make _thread.start_new_thread delete state of new thread on its startup failure

Lib/test/test_threading.py

@@ -1106,6 +1106,26 @@ def exit_handler():
         self.assertEqual(out, b'')
         self.assertIn(b"can't create new thread at interpreter shutdown", err)
 
+    def test_start_new_thread_failed(self):
+        # gh-109746: if Python fails to start newly created thread
+        # due to failure of underlying PyThread_start_new_thread() call,
+        # its state should be removed from interpreter' thread states list
+        # to avoid its double cleanup
+        code = """if 1:
+            import resource
+            import threading
+
+            resource.setrlimit(resource.RLIMIT_NPROC, (150, 150))
+
+            while True:
+                t = threading.Thread()
+                t.start()
+                t.join()
+        """
+        _, out, err = assert_python_failure("-c", code)
+        self.assertEqual(out, b'')
+        self.assertIn(b"can't start new thread", err)
+
 class ThreadJoinOnShutdown(BaseTestCase):
 
     def _run_and_join(self, script):

Misc/NEWS.d/next/Core and Builtins/2023-09-22-21-01-56.gh-issue-109746.32MHt9.rst

@@ -0,0 +1 @@
+If :func:`!_thread.start_new_thread` fails to start a new thread, it deletes its state from interpreter and thus avoids its repeated cleanup on finalization.

Modules/_threadmodule.c

@@ -1295,6 +1295,7 @@ do_start_new_thread(thread_module_state* state,
     if (err) {
         PyErr_SetString(ThreadError, "can't start new thread");
         PyThreadState_Clear(boot->tstate);
+        PyThreadState_Delete(boot->tstate);
         thread_bootstate_free(boot, 1);
         return -1;
     }

Python/pystate.c

@@ -1591,7 +1591,9 @@ tstate_delete_common(PyThreadState *tstate)
     if (tstate->_status.bound_gilstate) {
         unbind_gilstate_tstate(tstate);
     }
-    unbind_tstate(tstate);
+    if (tstate->_status.bound) {
+        unbind_tstate(tstate);
+    }
 
     // XXX Move to PyThreadState_Clear()?
     clear_datastack(tstate);