[GitHub] [hive] dengzhhu653 commented on a change in pull request #2693: HIVE-25582: Empty result when using offset limit with MR

[GitBox <gi...@apache.org>]

dengzhhu653 commented on a change in pull request #2693:
URL: https://github.com/apache/hive/pull/2693#discussion_r752141014



##########
File path: ql/src/java/org/apache/hadoop/hive/ql/exec/mr/ObjectCache.java
##########
@@ -18,82 +18,66 @@
 
 package org.apache.hadoop.hive.ql.exec.mr;
 
+import java.util.Map;
 import java.util.concurrent.Callable;
-import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.TimeoutException;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
+
 import org.apache.hadoop.hive.ql.metadata.HiveException;
 
 /**
- * ObjectCache. No-op implementation on MR we don't have a means to reuse
- * Objects between runs of the same task.
+ * ObjectCache. Simple implementation on MR we don't have a means to reuse
+ * Objects between runs of the same task, this acts as a local cache.
  *
  */
 public class ObjectCache implements org.apache.hadoop.hive.ql.exec.ObjectCache {
 
   private static final Logger LOG = LoggerFactory.getLogger(ObjectCache.class.getName());
 
+  private final Map<String, Object> cache = new ConcurrentHashMap<>();
+
+  private static ExecutorService staticPool = Executors.newCachedThreadPool();
+
   @Override
   public void release(String key) {
     // nothing to do
     LOG.debug("{} no longer needed", key);
+    cache.remove(key);
   }
 
   @Override
   public <T> T retrieve(String key) throws HiveException {
-    return retrieve(key, null);
+    return (T) cache.get(key);
   }
 
   @Override
   public <T> T retrieve(String key, Callable<T> fn) throws HiveException {
+    T value = (T) cache.get(key);
+    if (value != null || fn == null) {
+      return value;
+    }
     try {
       LOG.debug("Creating {}", key);
-      return fn.call();
+      value = fn.call();
     } catch (Exception e) {
       throw new HiveException(e);
     }
+    T previous = (T) cache.putIfAbsent(key, value);
+    return previous != null ? previous : value;
   }
 
   @Override
   public <T> Future<T> retrieveAsync(String key, Callable<T> fn) throws HiveException {
-    final T value = retrieve(key, fn);
-
-    return new Future<T>() {
-
-      @Override
-      public boolean cancel(boolean mayInterruptIfRunning) {
-        return false;
-      }
-
-      @Override
-      public boolean isCancelled() {
-        return false;
-      }
-
-      @Override
-      public boolean isDone() {
-        return true;
-      }
-
-      @Override
-      public T get() throws InterruptedException, ExecutionException {
-        return value;
-      }
-
-      @Override
-      public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException,
-          TimeoutException {
-        return value;
-      }
-    };
+    return staticPool.submit((Callable)() -> retrieve(key, fn));

Review comment:
       Done




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