No enqueue

qcodes/loops.py

@@ -409,7 +409,7 @@ def run_temp(self, **kwargs):
         return self.run(background=False, quiet=True,
                         data_manager=False, location=False, **kwargs)
 
-    def run(self, background=True, use_threads=True, enqueue=False,
+    def run(self, background=True, use_threads=True,
             quiet=False, data_manager=None, **kwargs):
         '''
         execute this loop
@@ -419,8 +419,6 @@ def run(self, background=True, use_threads=True, enqueue=False,
         use_threads: (default True): whenever there are multiple `get` calls
             back-to-back, execute them in separate threads so they run in
             parallel (as long as they don't block each other)
-        enqueue: (default False): wait for a previous background sweep to
-            finish? If false, will raise an error if another sweep is running
         quiet: (default False): set True to not print anything except errors
         data_manager: a DataManager instance (omit to use default,
             False to store locally)
@@ -446,11 +444,11 @@ def run(self, background=True, use_threads=True, enqueue=False,
 
         prev_loop = get_bg()
         if prev_loop:
-            if enqueue:
-                prev_loop.join()  # wait until previous loop finishes
-            else:
-                raise RuntimeError(
-                    'a loop is already running in the background')
+            if not quiet:
+                print('Waiting for the previous background Loop to finish...',
+                      flush=True)
+            prev_loop.join()
+
         if data_manager is False:
             data_mode = DataMode.LOCAL
         else:
@@ -461,6 +459,10 @@ def run(self, background=True, use_threads=True, enqueue=False,
         self.set_common_attrs(data_set=data_set, use_threads=use_threads,
                               signal_queue=self.signal_queue)
 
+        if prev_loop and not quiet:
+            print('...done. Starting ' + (data_set.location or 'new loop'),
+                  flush=True)
+
         if background:
             p = QcodesProcess(target=self._run_wrapper, name=MP_NAME)
             p.is_sweep = True

qcodes/tests/test_loop.py

@@ -106,12 +106,28 @@ def test_foreground_no_datamanager(self):
     def test_enqueue(self):
         c1 = self.gates.chan1
         loop = Loop(c1[1:5:1], 0.01).each(c1)
-        loop.run(location=self.location, quiet=True)
+        data1 = loop.run(location=self.location, quiet=True)
+
+        # second running of the loop should be enqueued, blocks until
+        # the first one finishes.
+        # TODO: check what it prints?
+        data2 = loop.run(location=self.location2, quiet=True)
+
+        data1.sync()
+        data2.sync()
+        self.assertEqual(data1.chan1.tolist(), [1, 2, 3, 4])
+        for v in data2.chan1:
+            self.assertTrue(np.isnan(v))
 
-        with self.assertRaises(RuntimeError):
-            loop.run(location=self.location2, quiet=True)
-        loop.run(location=self.location2, quiet=True, enqueue=True)
         loop.process.join()
+        data2.sync()
+        self.assertEqual(data2.chan1.tolist(), [1, 2, 3, 4])
+
+        # and while we're here, check that running a loop in the
+        # foreground *after* the background clears its .process
+        self.assertTrue(hasattr(loop, 'process'))
+        loop.run_temp()
+        self.assertFalse(hasattr(loop, 'process'))
 
 
 def sleeper(t):