Optimize Iterator<ImmutableBitmap> implementation inside Filters.matchPredicate() so that it doesn't emit empty bitmap in the end of the iteration, and make it to follow Iterator contract, that is throw NoSuchElementException from next() if there are no more bitmaps (#3754)

processing/src/main/java/io/druid/segment/filter/Filters.java

@@ -43,6 +43,7 @@ import io.druid.segment.data.Indexed;
 import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;
+import java.util.NoSuchElementException;
 
 /**
  */
@@ -141,26 +142,42 @@ public class Filters
           {
             return new Iterator<ImmutableBitmap>()
             {
-              int currIndex = 0;
+              private final int bitmapIndexCardinality = bitmapIndex.getCardinality();
+              private int nextIndex = 0;
+              private ImmutableBitmap nextBitmap;
+
+              {
+                findNextBitmap();
+              }
+
+              private void findNextBitmap()
+              {
+                while (nextIndex < bitmapIndexCardinality) {
+                  if (predicate.apply(dimValues.get(nextIndex))) {
+                    nextBitmap = bitmapIndex.getBitmap(nextIndex);
+                    nextIndex++;
+                    return;
+                  }
+                  nextIndex++;
+                }
+                nextBitmap = null;
+              }
 
               @Override
               public boolean hasNext()
               {
-                return currIndex < bitmapIndex.getCardinality();
+                return nextBitmap != null;
               }
 
               @Override
               public ImmutableBitmap next()
               {
-                while (currIndex < bitmapIndex.getCardinality() && !predicate.apply(dimValues.get(currIndex))) {
+                ImmutableBitmap bitmap = nextBitmap;
-                  currIndex++;
+                if (bitmap == null) {
+                  throw new NoSuchElementException();
                 }
-
+                findNextBitmap();
-                if (currIndex == bitmapIndex.getCardinality()) {
+                return bitmap;
-                  return bitmapIndex.getBitmapFactory().makeEmptyImmutableBitmap();
-                }
-
-                return bitmapIndex.getBitmap(currIndex++);
               }
 
               @Override