clean packet context

@@ -6,6 +6,7 @@ import org.onlab.packet.Ethernet;
 import org.projectfloodlight.openflow.protocol.OFPacketIn;
 import org.projectfloodlight.openflow.protocol.OFPacketOut;
 import org.projectfloodlight.openflow.protocol.action.OFAction;
+import org.projectfloodlight.openflow.protocol.action.OFActionOutput;
 import org.projectfloodlight.openflow.types.OFBufferId;
 import org.projectfloodlight.openflow.types.OFPort;
 
@@ -36,21 +37,26 @@ public final class DefaultPacketContext implements PacketContext {
     }
 
     @Override
-    public void build(OFPort outPort) {
+    public synchronized void build(OFPort outPort) {
+        if (isBuilt) {
+            return;
+        }
+        OFPacketOut.Builder builder = sw.factory().buildPacketOut();
+        OFAction act = buildOutput(outPort.getPortNumber());
+        pktout = builder.setXid(pktin.getXid())
+                .setBufferId(pktin.getBufferId())
+                .setActions(Collections.singletonList(act))
+                .build();
         isBuilt = true;
-
     }
 
     @Override
-    public void build(Ethernet ethFrame, OFPort outPort) {
+    public synchronized void build(Ethernet ethFrame, OFPort outPort) {
         if (isBuilt) {
             return;
         }
         OFPacketOut.Builder builder = sw.factory().buildPacketOut();
-        OFAction act = sw.factory().actions()
-                .buildOutput()
-                .setPort(OFPort.of(outPort.getPortNumber()))
-                .build();
+        OFAction act = buildOutput(outPort.getPortNumber());
         pktout = builder.setXid(pktin.getXid())
                 .setBufferId(OFBufferId.NO_BUFFER)
                 .setActions(Collections.singletonList(act))
@@ -85,4 +91,12 @@ public final class DefaultPacketContext implements PacketContext {
         return pktin.getData().clone();
     }
 
+    private OFActionOutput buildOutput(Integer port) {
+        OFActionOutput act = sw.factory().actions()
+                .buildOutput()
+                .setPort(OFPort.of(port))
+                .build();
+        return act;
+    }
+
 }