BUG-650: allocation-free ResolveDataChangeState.needsProcessing()

Critical path optimization. Based on logic introduced in previous
patches, we now know that when the inherited subtree listener iterable
is not a Collection, it is by definition non-empty. Use this knowledge
to elide Iterables.isEmpty() which is (relatively) costly due to
object allocation.

With this patch, ResolveDataChangeState.needsProcessing() does not
allocate any objects and relies on readily-available state to determine
whether additional processing is required.

Change-Id: I0322e0a8f58165f695f2284116057d03e2d4cb45
Signed-off-by: Robert Varga <rovarga@cisco.com>

diff --git a/opendaylight/md-sal/sal-inmemory-datastore/src/main/java/org/opendaylight/controller/md/sal/dom/store/impl/ResolveDataChangeState.java b/opendaylight/md-sal/sal-inmemory-datastore/src/main/java/org/opendaylight/controller/md/sal/dom/store/impl/ResolveDataChangeState.java
index e18b632275b88f51e713468f1bf1ca7de6c24dfb..3db4115af67908bed3c4edfcfbb2d91cdae3baae 100644 (file)
--- a/opendaylight/md-sal/sal-inmemory-datastore/src/main/java/org/opendaylight/controller/md/sal/dom/store/impl/ResolveDataChangeState.java
+++ b/opendaylight/md-sal/sal-inmemory-datastore/src/main/java/org/opendaylight/controller/md/sal/dom/store/impl/ResolveDataChangeState.java
@@ -175,12 +175,25 @@ final class ResolveDataChangeState {
         if (!inheritedOne.isEmpty()) {
             return true;
         }
-        // Have SUBTREE listeners
-        if (!Iterables.isEmpty(inheritedSub)) {
-            return true;
+
+        /*
+         * Have SUBTREE listeners
+         *
+         * This is slightly magical replacement for !Iterables.isEmpty(inheritedSub).
+         * It relies on the logic in child(), which gives us the guarantee that when
+         * inheritedSub is not a Collection, it is guaranteed to be non-empty (which
+         * means we need to process). If it is a collection, we still need to check
+         * it for emptiness.
+         *
+         * Unlike Iterables.isEmpty() this code does not instantiate any temporary
+         * objects and is thus more efficient.
+         */
+        if (inheritedSub instanceof Collection) {
+            return !((Collection<?>) inheritedSub).isEmpty();
         }
 
-        return false;
+        // Non-Collection => non-empty => have to process
+        return true;
     }
 
     /**