bpo-33097: Fix submit accepting callable after executor shutdown by interpreter exit (GH-6144)

Executors in concurrent.futures accepted tasks after executor was shutdown by interpreter exit. Tasks were left in PENDING state forever. This fix changes submit to instead raise a RuntimeError.

Lib/test/test_concurrent_futures.py

@@ -303,6 +303,34 @@ class ExecutorShutdownTest:
         self.assertFalse(err)
         self.assertEqual(out.strip(), b"apple")
 
+    def test_submit_after_interpreter_shutdown(self):
+        # Test the atexit hook for shutdown of worker threads and processes
+        rc, out, err = assert_python_ok('-c', """if 1:
+            import atexit
+            @atexit.register
+            def run_last():
+                try:
+                    t.submit(id, None)
+                except RuntimeError:
+                    print("runtime-error")
+                    raise
+            from concurrent.futures import {executor_type}
+            if __name__ == "__main__":
+                context = '{context}'
+                if not context:
+                    t = {executor_type}(5)
+                else:
+                    from multiprocessing import get_context
+                    context = get_context(context)
+                    t = {executor_type}(5, mp_context=context)
+                    t.submit(id, 42).result()
+            """.format(executor_type=self.executor_type.__name__,
+                       context=getattr(self, "ctx", "")))
+        # Errors in atexit hooks don't change the process exit code, check
+        # stderr manually.
+        self.assertIn("RuntimeError: cannot schedule new futures", err.decode())
+        self.assertEqual(out.strip(), b"runtime-error")
+
     def test_hang_issue12364(self):
         fs = [self.executor.submit(time.sleep, 0.1) for _ in range(50)]
         self.executor.shutdown()