HADOOP-17608. Fix NPE in TestKMS (#2828)

hadoop-common-project/hadoop-kms/src/test/java/org/apache/hadoop/crypto/key/kms/server/TestKMS.java

@@ -18,6 +18,8 @@
 package org.apache.hadoop.crypto.key.kms.server;
 
 import java.util.function.Supplier;
+
+import org.apache.commons.lang3.ThreadUtils;
 import org.apache.hadoop.thirdparty.com.google.common.cache.LoadingCache;
 import org.apache.curator.test.TestingServer;
 import org.apache.hadoop.conf.Configuration;
@@ -525,6 +527,7 @@ public class TestKMS {
     if (ssl) {
       sslFactory = new SSLFactory(SSLFactory.Mode.CLIENT, conf);
       try {
+        // the first reloader thread is created here
         sslFactory.init();
       } catch (GeneralSecurityException ex) {
         throw new IOException(ex);
@@ -541,31 +544,29 @@ public class TestKMS {
         final URI uri = createKMSUri(getKMSUrl());
 
         if (ssl) {
+          // the second reloader thread is created here
           KeyProvider testKp = createProvider(uri, conf);
-          ThreadGroup threadGroup = Thread.currentThread().getThreadGroup();
-          while (threadGroup.getParent() != null) {
-            threadGroup = threadGroup.getParent();
-          }
-          Thread[] threads = new Thread[threadGroup.activeCount()];
-          threadGroup.enumerate(threads);
-          Thread reloaderThread = null;
-          for (Thread thread : threads) {
-            if ((thread.getName() != null)
-                && (thread.getName().contains(SSL_RELOADER_THREAD_NAME))) {
-              reloaderThread = thread;
-            }
-          }
-          Assert.assertTrue("Reloader is not alive", reloaderThread.isAlive());
-          // Explicitly close the provider so we can verify the internal thread
-          // is shutdown
+          Collection<Thread> reloaderThreads =
+              ThreadUtils.findThreadsByName(SSL_RELOADER_THREAD_NAME);
+          // now there are two active reloader threads
+          assertEquals(2, reloaderThreads.size());
+          // Explicitly close the provider so we can verify
+          // the second reloader thread is shutdown
           testKp.close();
           boolean reloaderStillAlive = true;
           for (int i = 0; i < 10; i++) {
-            reloaderStillAlive = reloaderThread.isAlive();
-            if (!reloaderStillAlive) break;
+            for (Thread thread : reloaderThreads) {
+              if (!thread.isAlive()) {
+                reloaderStillAlive = false;
+                break;
+              }
+            }
             Thread.sleep(1000);
           }
           Assert.assertFalse("Reloader is still alive", reloaderStillAlive);
+          reloaderThreads =
+              ThreadUtils.findThreadsByName(SSL_RELOADER_THREAD_NAME);
+          assertEquals(1, reloaderThreads.size());
         }
 
         if (kerberos) {