MAPREDUCE-7302. Upgrading to JUnit 4.13 causes testcase TestFetcher.testCorruptedIFile() to fail. Contributed by Peter Bacsko. Reviewed by Akira Ajisaka.

(cherry picked from commit da93cd962c8d19874d09360726628cdde8595a7d)

Conflicts:
	hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/ReadaheadPool.java

(cherry picked from commit 7ad844ee9ed7eaab4fbb4d38576be10d497460cf)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/ReadaheadPool.java

@@ -29,6 +29,7 @@ import org.apache.hadoop.io.nativeio.NativeIO;
 
 import static org.apache.hadoop.io.nativeio.NativeIO.POSIX.POSIX_FADV_WILLNEED;
 
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
 import com.google.common.util.concurrent.ThreadFactoryBuilder;
 import org.slf4j.Logger;
@@ -59,7 +60,17 @@ public class ReadaheadPool {
       return instance;
     }
   }
-  
+
+  @VisibleForTesting
+  public static void resetInstance() {
+    synchronized (ReadaheadPool.class) {
+      if (instance != null) {
+        instance.pool.shutdownNow();
+        instance = null;
+      }
+    }
+  }
+
   private ReadaheadPool() {
     pool = new ThreadPoolExecutor(POOL_SIZE, MAX_POOL_SIZE, 3L, TimeUnit.SECONDS,
         new ArrayBlockingQueue<Runnable>(CAPACITY));

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/test/java/org/apache/hadoop/mapreduce/task/reduce/TestFetcher.java

@@ -47,6 +47,7 @@ import java.util.ArrayList;
 
 import javax.crypto.SecretKey;
 
+import org.apache.hadoop.io.ReadaheadPool;
 import org.apache.hadoop.io.Text;
 import org.apache.hadoop.mapred.Counters;
 import org.apache.hadoop.mapred.IFileInputStream;
@@ -93,6 +94,8 @@ public class TestFetcher {
   @SuppressWarnings("unchecked") // mocked generics
   public void setup() {
     LOG.info(">>>> " + name.getMethodName());
+    // to avoid threading issues with JUnit 4.13+
+    ReadaheadPool.resetInstance();
     job = new JobConf();
     job.setBoolean(MRJobConfig.SHUFFLE_FETCH_RETRY_ENABLED, false);
     jobWithRetry = new JobConf();