Small cleanups and performance improvements in o.e.c.u.concurrent.AtomicArray

Some small obvious cleanups in AtomicArray, drying up a volatile hack,
removing some redundant and potentially buggy volatile access and
simplifying (and for large arrays also speeding up) the API for copying the contents to an array.

Author: original-brownbear

server/src/main/java/org/elasticsearch/action/bulk/BulkOperation.java

@@ -323,9 +323,7 @@ private void redirectFailuresOrCompleteBulkOperation() {
     }
 
     private void completeBulkOperation() {
-        listener.onResponse(
-            new BulkResponse(responses.toArray(new BulkItemResponse[responses.length()]), buildTookInMillis(startTimeNanos))
-        );
+        listener.onResponse(new BulkResponse(responses.toArray(BulkItemResponse.class), buildTookInMillis(startTimeNanos)));
         // Allow memory for bulk shard request items to be reclaimed before all items have been completed
         bulkRequest = null;
     }

server/src/main/java/org/elasticsearch/action/bulk/TransportSimulateBulkAction.java

@@ -99,7 +99,7 @@ protected void createMissingIndicesAndIndexData(
                 )
             );
         }
-        listener.onResponse(new BulkResponse(responses.toArray(new BulkItemResponse[responses.length()]), buildTookInMillis(startTime)));
+        listener.onResponse(new BulkResponse(responses.toArray(BulkItemResponse.class), buildTookInMillis(startTime)));
     }
 
     /*

server/src/main/java/org/elasticsearch/action/get/TransportMultiGetAction.java

@@ -99,7 +99,7 @@ protected void doExecute(Task task, final MultiGetRequest request, final ActionL
 
         if (shardRequests.isEmpty()) {
             // only failures..
-            listener.onResponse(new MultiGetResponse(responses.toArray(new MultiGetItemResponse[responses.length()])));
+            listener.onResponse(new MultiGetResponse(responses.toArray(MultiGetItemResponse.class)));
         }
 
         executeShardAction(listener, responses, shardRequests);
@@ -138,7 +138,7 @@ public void onFailure(Exception e) {
                 }
 
                 private void finishHim() {
-                    delegate.onResponse(new MultiGetResponse(responses.toArray(new MultiGetItemResponse[responses.length()])));
+                    delegate.onResponse(new MultiGetResponse(responses.toArray(MultiGetItemResponse.class)));
                 }
             });
         }

server/src/main/java/org/elasticsearch/action/search/TransportMultiSearchAction.java

@@ -189,7 +189,7 @@ private void handleResponse(final int responseSlot, final MultiSearchResponse.It
             private void finish() {
                 ActionListener.respondAndRelease(
                     listener,
-                    new MultiSearchResponse(responses.toArray(new MultiSearchResponse.Item[responses.length()]), buildTookInMillis())
+                    new MultiSearchResponse(responses.toArray(MultiSearchResponse.Item.class), buildTookInMillis())
                 );
             }
 

server/src/main/java/org/elasticsearch/action/termvectors/TransportMultiTermVectorsAction.java

@@ -101,7 +101,7 @@ protected void doExecute(Task task, final MultiTermVectorsRequest request, final
 
         if (shardRequests.size() == 0) {
             // only failures..
-            listener.onResponse(new MultiTermVectorsResponse(responses.toArray(new MultiTermVectorsItemResponse[responses.length()])));
+            listener.onResponse(new MultiTermVectorsResponse(responses.toArray(MultiTermVectorsItemResponse.class)));
         }
 
         executeShardAction(listener, responses, shardRequests);
@@ -148,9 +148,7 @@ public void onFailure(Exception e) {
                 }
 
                 private void finishHim() {
-                    listener.onResponse(
-                        new MultiTermVectorsResponse(responses.toArray(new MultiTermVectorsItemResponse[responses.length()]))
-                    );
+                    listener.onResponse(new MultiTermVectorsResponse(responses.toArray(MultiTermVectorsItemResponse.class)));
                 }
             });
         }

server/src/main/java/org/elasticsearch/cluster/metadata/MetadataIndexStateService.java

@@ -638,7 +638,7 @@ public void onFailure(Exception e) {
 
                     private void processIfFinished() {
                         if (countDown.countDown()) {
-                            onResponse.accept(new IndexResult(index, results.toArray(new ShardResult[results.length()])));
+                            onResponse.accept(new IndexResult(index, results.toArray(ShardResult.class)));
                         }
                     }
                 }));
@@ -768,7 +768,7 @@ public void onFailure(Exception e) {
 
                     private void processIfFinished() {
                         if (countDown.countDown()) {
-                            AddBlockResult result = new AddBlockResult(index, results.toArray(new AddBlockShardResult[results.length()]));
+                            AddBlockResult result = new AddBlockResult(index, results.toArray(AddBlockShardResult.class));
                             logger.debug("result of applying block to index {}: {}", index, result);
                             onResponse.accept(result);
                         }

server/src/main/java/org/elasticsearch/common/util/concurrent/AtomicArray.java

@@ -8,8 +8,7 @@
 
 package org.elasticsearch.common.util.concurrent;
 
-import org.elasticsearch.ElasticsearchGenerationException;
-
+import java.lang.reflect.Array;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -59,15 +58,17 @@ public int nonNullLength() {
      */
     public void set(int i, E value) {
         array.set(i, value);
-        if (nonNullList != null) { // read first, lighter, and most times it will be null...
-            nonNullList = null;
-        }
+        resetCachedList();
     }
 
     public final void setOnce(int i, E value) {
         if (array.compareAndSet(i, null, value) == false) {
             throw new IllegalStateException("index [" + i + "] has already been set");
         }
+        resetCachedList();
+    }
+
+    private void resetCachedList() {
         if (nonNullList != null) { // read first, lighter, and most times it will be null...
             nonNullList = null;
         }
@@ -87,9 +88,10 @@ public E get(int i) {
      * Returns the it as a non null list.
      */
     public List<E> asList() {
-        if (nonNullList == null) {
-            if (array == null || array.length() == 0) {
-                nonNullList = Collections.emptyList();
+        var res = nonNullList;
+        if (res == null) {
+            if (array.length() == 0) {
+                res = Collections.emptyList();
             } else {
                 List<E> list = new ArrayList<>(array.length());
                 for (int i = 0; i < array.length(); i++) {
@@ -98,20 +100,20 @@ public List<E> asList() {
                         list.add(e);
                     }
                 }
-                nonNullList = list;
+                res = list;
             }
+            nonNullList = res;
         }
-        return nonNullList;
+        return res;
     }
 
     /**
      * Copies the content of the underlying atomic array to a normal one.
      */
-    public E[] toArray(E[] a) {
-        if (a.length != array.length()) {
-            throw new ElasticsearchGenerationException("AtomicArrays can only be copied to arrays of the same size");
-        }
-        for (int i = 0; i < array.length(); i++) {
+    public E[] toArray(Class<E> clazz) {
+        @SuppressWarnings("unchecked")
+        E[] a = (E[]) Array.newInstance(clazz, array.length());
+        for (int i = 0; i < a.length; i++) {
             a[i] = array.get(i);
         }
         return a;