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From GitBox <...@apache.org>
Subject [GitHub] keith-turner commented on a change in pull request #969: [WIP] Issue-967
Date Thu, 01 Jan 1970 00:00:00 GMT
keith-turner commented on a change in pull request #969: [WIP] Issue-967
URL: https://github.com/apache/fluo/pull/969#discussion_r152160862
 
 

 ##########
 File path: modules/core/src/main/java/org/apache/fluo/core/impl/AsyncReader.java
 ##########
 @@ -0,0 +1,101 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more contributor license
+ * agreements. See the NOTICE file distributed with this work for additional information
regarding
+ * copyright ownership. The ASF licenses this file to you under the Apache License, Version
2.0 (the
+ * "License"); you may not use this file except in compliance with the License. You may obtain
a
+ * copy of the License at
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software distributed under
the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
express
+ * or implied. See the License for the specific language governing permissions and limitations
under
+ * the License.
+ */
+
+package org.apache.fluo.core.impl;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.LinkedBlockingQueue;
+
+import com.google.common.collect.Collections2;
+import org.apache.fluo.api.data.Bytes;
+import org.apache.fluo.api.data.Column;
+import org.apache.fluo.api.data.RowColumn;
+import org.apache.fluo.core.impl.TransactionImpl;
+
+public class AsyncReader {
+  private BlockingQueue<AsyncGet> asyncGetsQueue;
+  private ExecutorService executorService;
+  private TransactionImpl tx;
+
+  public AsyncReader(TransactionImpl tx) {
+    this.tx = tx;
+    asyncGetsQueue = new LinkedBlockingQueue<>();
+    executorService = Executors.newSingleThreadExecutor();
+  }
+
+  public CompletableFuture<Bytes> get(Bytes row, Column column) {
+    return get(row, column, null);
+  }
+
+  public CompletableFuture<Bytes> get(Bytes row, Column column, Bytes defaultValue)
{
+    AsyncGet curAsyncGet = new AsyncGet(row, column, defaultValue);
+    asyncGetsQueue.add(curAsyncGet);
+
+    executorService.submit(() -> {
+      List<AsyncGet> getsList = new ArrayList<>();
+      asyncGetsQueue.drainTo(getsList);
+
+      try {
+        Collection<RowColumn> rowColumns = Collections2.transform(getsList, ag ->
ag.rc);
+
+        Map<RowColumn, Bytes> getsMap = tx.get(rowColumns);
+
+        for (AsyncGet asyncGet : getsList) {
+          Bytes result = getsMap.get(asyncGet.rc);
+          asyncGet.res.complete(result == null ? defaultValue : result);
+          getsList.remove(asyncGet);
 
 Review comment:
   The following comments are moot because I don't think things needs to be removed based
on earlier comment.  Just sharing some knowledge in following comments.
   
   This could cause a concurrent modification exception.  The foreach has a hidden iterator.
 In java, many iterators will throw a concurrent modification exception if the collection
is modified during iteration.  Using a while loop with an explicit iterator and calling remove
on the iterator is the best way to remove while iterating.  
   
   Also removing items from an arraylist could be an O(N^2) operation.  In the situation of
removing from the middle of a list a linked list may be better.

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