Workaround for ConcurrentModificationException

- Workaround fix for ONOS-1193
- If locking the whole link collection damages the performance,
  apply the fix suggested on GossipLinkStore comment.

Change-Id: Idd4d2e5b8e3a50843fe7abd10a615cfbd9a16478

@@ -246,6 +246,18 @@ public class GossipLinkStore
     @Override
     public Set<Link> getEgressLinks(ConnectPoint src) {
         Set<Link> egress = new HashSet<>();
+        //
+        // Change `srcLinks` to ConcurrentMap<DeviceId, (Concurrent)Set>
+        // to remove this synchronized block, if we hit performance issue.
+        // SetMultiMap#get returns wrapped collection to provide modifiable-view.
+        // And the wrapped collection is not concurrent access safe.
+        //
+        // Our use case here does not require returned collection to be modifiable,
+        // so the wrapped collection forces us to lock the whole multiset,
+        // for benefit we don't need.
+        //
+        // Same applies to `dstLinks`
+        synchronized (srcLinks) {
             for (LinkKey linkKey : srcLinks.get(src.deviceId())) {
                 if (linkKey.src().equals(src)) {
                     Link link = links.get(linkKey);
@@ -256,12 +268,14 @@ public class GossipLinkStore
                     }
                 }
             }
+        }
         return egress;
     }
 
     @Override
     public Set<Link> getIngressLinks(ConnectPoint dst) {
         Set<Link> ingress = new HashSet<>();
+        synchronized (dstLinks) {
             for (LinkKey linkKey : dstLinks.get(dst.deviceId())) {
                 if (linkKey.dst().equals(dst)) {
                     Link link = links.get(linkKey);
@@ -272,6 +286,7 @@ public class GossipLinkStore
                     }
                 }
             }
+        }
         return ingress;
     }
 

@@ -146,22 +146,26 @@ public class SimpleLinkStore
     @Override
     public Set<Link> getEgressLinks(ConnectPoint src) {
         Set<Link> egress = new HashSet<>();
+        synchronized (srcLinks) {
             for (LinkKey linkKey : srcLinks.get(src.deviceId())) {
                 if (linkKey.src().equals(src)) {
                     egress.add(links.get(linkKey));
                 }
             }
+        }
         return egress;
     }
 
     @Override
     public Set<Link> getIngressLinks(ConnectPoint dst) {
         Set<Link> ingress = new HashSet<>();
+        synchronized (dstLinks) {
             for (LinkKey linkKey : dstLinks.get(dst.deviceId())) {
                 if (linkKey.dst().equals(dst)) {
                     ingress.add(links.get(linkKey));
                 }
             }
+        }
         return ingress;
     }