fix regression - reintroducing the safety check removed in commit-1d602be

processing/src/main/java/io/druid/segment/incremental/IncrementalIndexStorageAdapter.java

@@ -60,6 +60,8 @@
 
 import javax.annotation.Nullable;
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
@@ -361,34 +363,43 @@ public IndexedInts getRow()
                     final int[][] dims = currEntry.getKey().getDims();
 
                     int[] indices = dimIndex < dims.length ? dims[dimIndex] : null;
-                    if (indices == null) {
-                      indices = new int[0];
-                    }
-                    // check for null entry
-                    if (indices.length == 0 && dimValLookup.contains(null)) {
-                      indices = new int[] { dimValLookup.getId(null) };
-                    }
 
-                    final int[] vals = indices;
+                    List<Integer> valsTmp = null;
+                    if ((indices == null || indices.length == 0) && dimValLookup.contains(null)) {
+                      int id = dimValLookup.getId(null);
+                      if (id < maxId) {
+                        valsTmp = new ArrayList<>(1);
+                        valsTmp.add(id);
+                      }
+                    } else if (indices != null && indices.length > 0) {
+                      valsTmp = new ArrayList<>(indices.length);
+                      for (int i = 0; i < indices.length; i++) {
+                        int id = indices[i];
+                        if (id < maxId) {
+                          valsTmp.add(id);
+                        }
+                      }
+                    }
 
+                    final List<Integer> vals = valsTmp == null ? Collections.EMPTY_LIST : valsTmp;
                     return new IndexedInts()
                     {
                       @Override
                       public int size()
                       {
-                        return vals.length;
+                        return vals.size();
                       }
 
                       @Override
                       public int get(int index)
                       {
-                        return vals[index];
+                        return vals.get(index);
                       }
 
                       @Override
                       public Iterator<Integer> iterator()
                       {
-                        return Ints.asList(vals).iterator();
+                        return vals.iterator();
                       }
 
                       @Override

processing/src/test/java/io/druid/segment/incremental/IncrementalIndexStorageAdapterTest.java

@@ -19,6 +19,7 @@
 
 package io.druid.segment.incremental;
 
+import com.google.common.base.Function;
 import com.google.common.base.Supplier;
 import com.google.common.base.Suppliers;
 import com.google.common.collect.ImmutableMap;
@@ -46,6 +47,8 @@
 import io.druid.query.topn.TopNResultValue;
 import io.druid.segment.Cursor;
 import io.druid.segment.DimensionSelector;
+import io.druid.segment.StorageAdapter;
+import io.druid.segment.data.IndexedInts;
 import io.druid.segment.filter.SelectorFilter;
 import org.joda.time.DateTime;
 import org.joda.time.Interval;
@@ -54,6 +57,7 @@
 import org.junit.runner.RunWith;
 import org.junit.runners.Parameterized;
 
+import javax.annotation.Nullable;
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
@@ -376,4 +380,76 @@ public void testFilterByNull() throws Exception
     MapBasedRow row = (MapBasedRow) results.get(0);
     Assert.assertEquals(ImmutableMap.of("billy", "hi", "cnt", 1L), row.getEvent());
   }
+
+  @Test
+  public void testCursoringAndIndexUpdationInterleaving() throws Exception
+  {
+    final IncrementalIndex index = indexCreator.createIndex();
+    final long timestamp = System.currentTimeMillis();
+
+    for (int i = 0; i < 2; i++) {
+      index.add(
+          new MapBasedInputRow(
+              timestamp,
+              Lists.newArrayList("billy"),
+              ImmutableMap.<String, Object>of("billy", "v1" + i)
+          )
+      );
+    }
+
+    final StorageAdapter sa = new IncrementalIndexStorageAdapter(index);
+
+    Sequence<Cursor> cursors = sa.makeCursors(
+        null, new Interval(timestamp - 60_000, timestamp + 60_000), QueryGranularity.ALL, false
+    );
+
+    Sequences.toList(
+        Sequences.map(
+            cursors,
+            new Function<Cursor, Object>()
+            {
+              @Nullable
+              @Override
+              public Object apply(Cursor cursor)
+              {
+                DimensionSelector dimSelector = cursor.makeDimensionSelector(
+                    new DefaultDimensionSpec(
+                        "billy",
+                        "billy"
+                    )
+                );
+                int cardinality = dimSelector.getValueCardinality();
+
+                //index gets more rows at this point, while other thread is iterating over the cursor
+                try {
+                  for (int i = 0; i < 1; i++) {
+                    index.add(
+                        new MapBasedInputRow(
+                            timestamp,
+                            Lists.newArrayList("billy"),
+                            ImmutableMap.<String, Object>of("billy", "v2" + i)
+                        )
+                    );
+                  }
+                }
+                catch (Exception ex) {
+                  throw new RuntimeException(ex);
+                }
+
+                // and then, cursoring continues in the other thread
+                while (!cursor.isDone()) {
+                  IndexedInts row = dimSelector.getRow();
+                  for (int i : row) {
+                    Assert.assertTrue(i < cardinality);
+                  }
+                  cursor.advance();
+                }
+
+                return null;
+              }
+            }
+        ),
+        new ArrayList<>()
+    );
+  }
 }