From dc8f814accab73f3b8fa318d8592d5c3e5b76bbf Mon Sep 17 00:00:00 2001
From: Roman Leventov <leventov@users.noreply.github.com>
Date: Wed, 7 Dec 2016 14:54:09 -0600
Subject: [PATCH] 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)

---
 .../java/io/druid/segment/filter/Filters.java | 37 ++++++++++++++-----
 1 file changed, 27 insertions(+), 10 deletions(-)

diff --git a/processing/src/main/java/io/druid/segment/filter/Filters.java b/processing/src/main/java/io/druid/segment/filter/Filters.java
index fb26bef42b4..eea3d1cf089 100644
--- a/processing/src/main/java/io/druid/segment/filter/Filters.java
+++ b/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))) {
-                  currIndex++;
+                ImmutableBitmap bitmap = nextBitmap;
+                if (bitmap == null) {
+                  throw new NoSuchElementException();
                 }
-
-                if (currIndex == bitmapIndex.getCardinality()) {
-                  return bitmapIndex.getBitmapFactory().makeEmptyImmutableBitmap();
-                }
-
-                return bitmapIndex.getBitmap(currIndex++);
+                findNextBitmap();
+                return bitmap;
               }
 
               @Override