ONOS-4018 - Enhance the DistributedRegionStore to make sure that a

device ID appears in at most one Region's list of devices.

Change-Id: I6d30fab2c09544c68f49b11682f08ee8ded060fe

@@ -169,6 +169,16 @@ public class DistributedRegionStore
 
     @Override
     public void addDevices(RegionId regionId, Collection<DeviceId> deviceIds) {
+        // Devices can only be a member in one region.  Remove the device if it belongs to
+        // a different region than the region for which we are attempting to add it.
+        for (DeviceId deviceId : deviceIds) {
+            Region region = getRegionForDevice(deviceId);
+            if ((region != null) && (!regionId.id().equals(region.id().id()))) {
+                Set<DeviceId> deviceIdSet1 = ImmutableSet.of(deviceId);
+                removeDevices(region.id(), deviceIdSet1);
+            }
+        }
+
         membershipRepo.compute(regionId, (id, existingDevices) -> {
             if (existingDevices == null) {
                 return ImmutableSet.copyOf(deviceIds);

@@ -137,6 +137,15 @@ public class DistributedRegionStoreTest {
         deviceIds = store.getRegionDevices(RID1);
         assertEquals("incorrect device count", 3, deviceIds.size());
 
+        // Test adding DID3 to RID2 but it is already in RID1.
+        // DID3 will be removed from RID1 and added to RID2.
+        Region r2 = store.createRegion(RID2, "R2", CAMPUS, MASTERS);
+        store.addDevices(RID2, ImmutableSet.of(DID3));
+        deviceIds = store.getRegionDevices(RID1);
+        assertEquals("incorrect device count", 2, deviceIds.size());
+        deviceIds = store.getRegionDevices(RID2);
+        assertEquals("incorrect device count", 1, deviceIds.size());
+
         store.removeDevices(RID1, ImmutableSet.of(DID2, DID3));
         deviceIds = store.getRegionDevices(RID1);
         assertEquals("incorrect device count", 1, deviceIds.size());