test_scheduler: Test for hang when exiting with running experiments

The respective code path in artiq.master.scheduler._mk_worker_method
wasn't previously covered.

artiq/test/test_scheduler.py

@@ -185,6 +185,49 @@ class SchedulerCase(unittest.TestCase):
 
         loop.run_until_complete(scheduler.stop())
 
+    def test_close_with_active_runs(self):
+        """Check scheduler exits with experiments still running"""
+        loop = self.loop
+
+        scheduler = Scheduler(_RIDCounter(0), {}, None)
+
+        expid_bg = _get_expid("BackgroundExperiment")
+        # Suppress the SystemExit backtrace when worker process is killed.
+        expid_bg["log_level"] = logging.CRITICAL
+        expid = _get_expid("EmptyExperiment")
+
+        background_running = asyncio.Event()
+        empty_ready = asyncio.Event()
+        background_completed = asyncio.Event()
+        def notify(mod):
+            if mod == {"path": [0],
+                       "value": "running",
+                       "key": "status",
+                       "action": "setitem"}:
+                background_running.set()
+            if mod == {"path": [0],
+                       "value": "deleting",
+                       "key": "status",
+                       "action": "setitem"}:
+                background_completed.set()
+            if mod == {"path": [1],
+                       "value": "prepare_done",
+                       "key": "status",
+                       "action": "setitem"}:
+                empty_ready.set()
+        scheduler.notifier.publish = notify
+
+        scheduler.start()
+        scheduler.submit("main", expid_bg, -99, None, False)
+        loop.run_until_complete(background_running.wait())
+
+        scheduler.submit("main", expid, 0, None, False)
+        loop.run_until_complete(empty_ready.wait())
+
+        # At this point, (at least) BackgroundExperiment is still running; make
+        # sure we can stop the scheduler without hanging.
+        loop.run_until_complete(scheduler.stop())
+
     def test_flush(self):
         loop = self.loop
         scheduler = Scheduler(_RIDCounter(0), dict(), None)