Eager cleanup of parameterized mini cluster resources.

Jenkins runs on the PR clearly shows that the peak thread usage
is dangerously close to the ulimits. Infact a bunch of failures
are with thread creation.

This patch eagerly cleans up the mini cluster resources from
previous parameterized runs so that they are not held up for longer
after each run.

Profiled the test runs using YourKit and I can see that the peak
thread usage substantially dropped.

hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestFromClientSide.java

@@ -145,8 +145,6 @@ public class TestFromClientSide {
   private static byte [] VALUE = Bytes.toBytes("testValue");
   protected static int SLAVES = 3;
 
-  private static final List<HBaseTestingUtility> tearDownClusters = new ArrayList<>();
-
   @Rule public TestTableName name = new TestTableName();
 
   // To keep the child classes happy.
@@ -174,6 +172,11 @@ protected static final void initialize(Class registryImpl, int numHedgedReqs, Cl
     // ((Log4JLogger)ScannerCallable.LOG).getLogger().setLevel(Level.ALL);
     // make sure that we do not get the same ts twice, see HBASE-19731 for more details.
     EnvironmentEdgeManager.injectEdge(new NonRepeatedEnvironmentEdge());
+    if (TEST_UTIL != null) {
+      // Belongs to another parameterized run. Currently, there is no clean way to cleanup test
+      // resources after each parametrized run. Something like @AfterParameterized.
+      TEST_UTIL.shutdownMiniCluster();
+    }
     TEST_UTIL = new HBaseTestingUtility();
     Configuration conf = TEST_UTIL.getConfiguration();
     conf.setStrings(CoprocessorHost.REGION_COPROCESSOR_CONF_KEY,
@@ -187,8 +190,6 @@ protected static final void initialize(Class registryImpl, int numHedgedReqs, Cl
       conf.setBoolean(HConstants.MASTER_REGISTRY_ENABLE_HEDGED_READS_KEY, true);
       conf.setInt(HConstants.HBASE_RPCS_HEDGED_REQS_FANOUT_KEY, numHedgedReqs);
     }
-    // We need more than one region server in this test
-    tearDownClusters.add(TEST_UTIL);
     StartMiniClusterOption.Builder builder = StartMiniClusterOption.builder();
     // Multiple masters needed only when hedged reads for master registry are enabled.
     builder.numMasters(numHedgedReqs > 1 ? 3 : 1).numRegionServers(SLAVES);
@@ -197,8 +198,8 @@ protected static final void initialize(Class registryImpl, int numHedgedReqs, Cl
 
   @AfterClass
   public static void tearDownAfterClass() throws Exception {
-    for (HBaseTestingUtility util: tearDownClusters) {
-      util.shutdownMiniCluster();
+    if (TEST_UTIL != null) {
+      TEST_UTIL.shutdownMiniCluster();
     }
   }
 

hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestScannersFromClientSide.java

@@ -91,16 +91,13 @@ public class TestScannersFromClientSide {
   private static byte [] QUALIFIER = Bytes.toBytes("testQualifier");
   private static byte [] VALUE = Bytes.toBytes("testValue");
 
-  // Cleaned up after the entire test is run.
-  private static List<HBaseTestingUtility> tearDownClusters = new ArrayList<>();
-
   @Rule
   public TestTableName name = new TestTableName();
 
   @AfterClass
   public static void tearDownAfterClass() throws Exception {
-    for (HBaseTestingUtility testingUtility: tearDownClusters) {
-      testingUtility.shutdownMiniCluster();
+    if (TEST_UTIL != null) {
+      TEST_UTIL.shutdownMiniCluster();
     }
   }
 
@@ -114,8 +111,12 @@ public static Collection parameters() {
   }
 
   public TestScannersFromClientSide(Class registryImpl, int numHedgedReqs) throws Exception {
+    if (TEST_UTIL != null) {
+      // Might be a remnant of another parameterized run. JUnit does not provide a hook to run after
+      // each parameterized test run.
+      TEST_UTIL.shutdownMiniCluster();
+    }
     TEST_UTIL = new HBaseTestingUtility();
-    tearDownClusters.add(TEST_UTIL);
     Configuration conf = TEST_UTIL.getConfiguration();
     conf.setLong(HConstants.HBASE_CLIENT_SCANNER_MAX_RESULT_SIZE_KEY, 10 * 1024 * 1024);
     conf.setClass(HConstants.REGISTRY_IMPL_CONF_KEY, registryImpl, AsyncRegistry.class);