HDFS-15818. Fix TestFsDatasetImpl.testReadLockCanBeDisabledByConfig. Contributed by Leon Gao (#2679)

(cherry picked from commit 9434c1e)

Author: LeonGao91

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestFsDatasetImpl.java

@@ -17,8 +17,7 @@
  */
 package org.apache.hadoop.hdfs.server.datanode.fsdataset.impl;
 
-import java.util.Arrays;
-import java.util.Collections;
+import java.util.concurrent.TimeoutException;
 import java.util.function.Supplier;
 import com.google.common.collect.Lists;
 
@@ -240,11 +239,12 @@ public void run() {
     waiter.join();
     // The holder thread is still holding the lock, but the waiter can still
     // run as the lock is a shared read lock.
+    // Otherwise test will timeout with deadlock.
     assertEquals(true, accessed.get());
     holder.interrupt();
   }
 
-  @Test(timeout=10000)
+  @Test(timeout=20000)
   public void testReadLockCanBeDisabledByConfig()
       throws Exception {
     HdfsConfiguration conf = new HdfsConfiguration();
@@ -253,58 +253,58 @@ public void testReadLockCanBeDisabledByConfig()
     MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf)
         .numDataNodes(1).build();
     try {
+      AtomicBoolean accessed = new AtomicBoolean(false);
       cluster.waitActive();
       DataNode dn = cluster.getDataNodes().get(0);
       final FsDatasetSpi<?> ds = DataNodeTestUtils.getFSDataset(dn);
 
       CountDownLatch latch = new CountDownLatch(1);
       CountDownLatch waiterLatch = new CountDownLatch(1);
-      // create a synchronized list and verify the order of elements.
-      List<Integer> syncList =
-          Collections.synchronizedList(new ArrayList<>());
-
-
       Thread holder = new Thread() {
         public void run() {
-          latch.countDown();
           try (AutoCloseableLock l = ds.acquireDatasetReadLock()) {
-            syncList.add(0);
-          } catch (Exception e) {
-            return;
-          }
-          try {
+            latch.countDown();
+            // wait for the waiter thread to access the lock.
             waiterLatch.await();
-            syncList.add(2);
-          } catch (InterruptedException e) {
+          } catch (Exception e) {
           }
         }
       };
 
       Thread waiter = new Thread() {
         public void run() {
           try {
-            // wait for holder to get into the critical section.
+            // Wait for holder to get ds read lock.
             latch.await();
           } catch (InterruptedException e) {
             waiterLatch.countDown();
+            return;
           }
           try (AutoCloseableLock l = ds.acquireDatasetReadLock()) {
-            syncList.add(1);
+            accessed.getAndSet(true);
+            // signal the holder thread.
             waiterLatch.countDown();
           } catch (Exception e) {
           }
         }
       };
       waiter.start();
       holder.start();
-
-      waiter.join();
+      // Wait for sometime to make sure we are in deadlock,
+      try {
+        GenericTestUtils.waitFor(() ->
+                accessed.get(),
+            100, 10000);
+        fail("Waiter thread should not execute.");
+      } catch (TimeoutException e) {
+      }
+      // Release waiterLatch to exit deadlock.
+      waiterLatch.countDown();
       holder.join();
-
-      // verify that the synchronized list has the correct sequence.
-      assertEquals(
-          "The sequence of checkpoints does not correspond to shared lock",
-          syncList, Arrays.asList(0, 1, 2));
+      waiter.join();
+      // After releasing waiterLatch water
+      // thread will be able to execute.
+      assertTrue(accessed.get());
     } finally {
       cluster.shutdown();
     }