Fix ML_SYNC_ON_FIELD_TO_GUARD_CHANGING_THAT_FIELD issue

Change-Id: I367514c698e825ccf6fda63104e2a51f51c190c4

@@ -32,6 +32,8 @@ import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 
 import static com.google.common.base.Preconditions.checkNotNull;
 
@@ -45,7 +47,8 @@ public class DefaultRoutingHandler {
     private HashMap<DeviceId, ECMPShortestPathGraph> currentEcmpSpgMap;
     private HashMap<DeviceId, ECMPShortestPathGraph> updatedEcmpSpgMap;
     private DeviceConfiguration config;
-    private Status populationStatus;
+    private final Lock statusLock = new ReentrantLock();
+    private volatile Status populationStatus;
 
     /**
      * Represents the default routing population status.
@@ -86,6 +89,8 @@ public class DefaultRoutingHandler {
      */
     public boolean populateAllRoutingRules() {
 
+        statusLock.lock();
+        try {
             populationStatus = Status.STARTED;
             rulePopulator.resetCounter();
             log.info("Starts to populate routing rules");
@@ -115,6 +120,9 @@ public class DefaultRoutingHandler {
             log.info("Completes routing rule population. Total # of rules pushed : {}",
                     rulePopulator.getCounter());
             return true;
+        } finally {
+            statusLock.unlock();
+        }
     }
 
     /**
@@ -127,7 +135,8 @@ public class DefaultRoutingHandler {
      */
     public boolean populateRoutingRulesForLinkStatusChange(Link linkFail) {
 
-        synchronized (populationStatus) {
+        statusLock.lock();
+        try {
 
             if (populationStatus == Status.STARTED) {
                 log.warn("Previous rule population is not finished.");
@@ -179,6 +188,8 @@ public class DefaultRoutingHandler {
                 log.warn("Failed to repopulate the rules.");
                 return false;
             }
+        } finally {
+            statusLock.unlock();
         }
     }
 
@@ -504,7 +515,8 @@ public class DefaultRoutingHandler {
      * ABORTED status when any groups required for flows is not set yet.
      */
     public void startPopulationProcess() {
-        synchronized (populationStatus) {
+        statusLock.lock();
+        try {
             if (populationStatus == Status.IDLE
                     || populationStatus == Status.SUCCEEDED
                     || populationStatus == Status.ABORTED) {
@@ -514,6 +526,8 @@ public class DefaultRoutingHandler {
                 log.warn("Not initiating startPopulationProcess as populationStatus is {}",
                          populationStatus);
             }
+        } finally {
+            statusLock.unlock();
         }
     }
 
@@ -522,13 +536,16 @@ public class DefaultRoutingHandler {
      * Mostly the process is aborted when the groups required are not set yet.
      */
     public void resumePopulationProcess() {
-        synchronized (populationStatus) {
+        statusLock.lock();
+        try {
             if (populationStatus == Status.ABORTED) {
                 populationStatus = Status.STARTED;
                 // TODO: we need to restart from the point aborted instead of
                 // restarting.
                 populateAllRoutingRules();
             }
+        } finally {
+            statusLock.unlock();
         }
     }
 }