Fix network restore loop

brian2/core/magic.py

@@ -489,3 +489,7 @@ def start_scope():
     included by the magic functions such as `run`.
     """
     BrianObject._scope_current_key += 1
+
+    # Run garbage collection here to destroy stale objects from previous runs
+    # preventing them from squatting on auto-generated names in the InstanceFollower
+    gc.collect()

brian2/core/network.py

@@ -543,14 +543,15 @@ def add(self, *objs):
         """
         for obj in objs:
             if isinstance(obj, BrianObject):
-                if obj._network is not None:
+                if obj._network is not None and obj._network != self.id:
                     raise RuntimeError(
                         f"{obj.name} has already been simulated, cannot "
                         "add it to the network. If you were "
                         "trying to remove and add an object to "
                         "temporarily stop it from being run, "
                         "set its active flag to False instead."
                     )
+                obj._network = self.id
                 self.objects.add(obj)
             else:
                 # allow adding values from dictionaries

brian2/tests/test_network.py

@@ -1922,6 +1922,33 @@ def test_negative_duration_in_net_run():
         net.run(-1 * second)
 
 
+@pytest.mark.codegen_independent
+def test_network_restore_loop():
+    # Issue 1814: Verify that running and restoring networks in a loop
+    # does not raise KeyError due to auto-generated clocks leaking iteratively
+    filename = tempfile.mktemp(suffix="state", prefix="brian_test")
+    try:
+        start_scope()
+        G = NeuronGroup(10, "v:1", name="G")
+        G.run_regularly("v += 0.1", dt=1 * ms)
+        net = Network(collect())
+        net.run(1 * ms)
+        net.store(filename=filename)
+
+        for i in range(2):
+            start_scope()
+            G = NeuronGroup(10, "v:1", name="G")
+            G.run_regularly("v += 0.1", dt=1 * ms)
+            net2 = Network(collect())
+            net2.restore(filename=filename)
+            net2.run(1 * ms)
+    finally:
+        try:
+            os.remove(filename)
+        except OSError:
+            pass
+
+
 if __name__ == "__main__":
     BrianLogger.log_level_warn()
     for t in [