Fixes an NPE in OFDPA pipeliners

- Introduced a new method to indicate whether the pipeliner is ready to receive objectives or not
- Ensure init() in OfDpa2Pipeline and OvsOfdpaPipeline can only be invoked once
  This is to avoid processing duplicated DEVICE_ADDED events introduced by gerrit 18899

Change-Id: Icb08935cb1f2761d7c98b5086fc27b6a0d8bc0cf
diff --git a/drivers/default/src/main/java/org/onosproject/driver/pipeline/ofdpa/Ofdpa2Pipeline.java b/drivers/default/src/main/java/org/onosproject/driver/pipeline/ofdpa/Ofdpa2Pipeline.java
index 17a2d86..d8b1f06 100644
--- a/drivers/default/src/main/java/org/onosproject/driver/pipeline/ofdpa/Ofdpa2Pipeline.java
+++ b/drivers/default/src/main/java/org/onosproject/driver/pipeline/ofdpa/Ofdpa2Pipeline.java
@@ -151,27 +151,36 @@
     private ScheduledExecutorService accumulatorExecutorService
         = newSingleThreadScheduledExecutor(groupedThreads("OfdpaPipeliner", "acc-%d", log));
 
+    protected AtomicBoolean ready = new AtomicBoolean(false);
+
     @Override
     public void init(DeviceId deviceId, PipelinerContext context) {
-        this.deviceId = deviceId;
+        if (!ready.getAndSet(true)) {
+            this.deviceId = deviceId;
 
-        serviceDirectory = context.directory();
-        coreService = serviceDirectory.get(CoreService.class);
-        flowRuleService = serviceDirectory.get(FlowRuleService.class);
-        groupService = serviceDirectory.get(GroupService.class);
-        flowObjectiveStore = context.store();
-        deviceService = serviceDirectory.get(DeviceService.class);
-        // Init the accumulator, if enabled
-        if (isAccumulatorEnabled(this)) {
-            accumulator = new ForwardingObjectiveAccumulator(context.accumulatorMaxObjectives(),
-                                                             context.accumulatorMaxBatchMillis(),
-                                                             context.accumulatorMaxIdleMillis());
+            serviceDirectory = context.directory();
+            coreService = serviceDirectory.get(CoreService.class);
+            flowRuleService = serviceDirectory.get(FlowRuleService.class);
+            groupService = serviceDirectory.get(GroupService.class);
+            flowObjectiveStore = context.store();
+            deviceService = serviceDirectory.get(DeviceService.class);
+            // Init the accumulator, if enabled
+            if (isAccumulatorEnabled(this)) {
+                accumulator = new ForwardingObjectiveAccumulator(context.accumulatorMaxObjectives(),
+                        context.accumulatorMaxBatchMillis(),
+                        context.accumulatorMaxIdleMillis());
+            }
+
+            initDriverId();
+            initGroupHander(context);
+
+            initializePipeline();
         }
+    }
 
-        initDriverId();
-        initGroupHander(context);
-
-        initializePipeline();
+    @Override
+    public boolean isReady() {
+        return ready.get();
     }
 
     void setupAccumulatorForTests(int maxFwd, int maxBatchMS, int maxIdleMS) {