HBASE-14968 ConcurrentModificationException in region close resulting in the region staying in closing state

hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/CoprocessorHost.java

@@ -103,8 +103,11 @@ public abstract class CoprocessorHost<E extends CoprocessorEnvironment> {
    */
   private static Set<String> coprocessorNames =
       Collections.synchronizedSet(new HashSet<String>());
+
   public static Set<String> getLoadedCoprocessors() {
-      return coprocessorNames;
+    synchronized (coprocessorNames) {
+      return new HashSet(coprocessorNames);
+    }
   }
 
   /**
@@ -348,6 +351,7 @@ public abstract class CoprocessorHost<E extends CoprocessorEnvironment> {
    */
   static class EnvironmentPriorityComparator
       implements Comparator<CoprocessorEnvironment> {
+    @Override
     public int compare(final CoprocessorEnvironment env1,
         final CoprocessorEnvironment env2) {
       if (env1.getPriority() < env2.getPriority()) {
@@ -436,6 +440,7 @@ public abstract class CoprocessorHost<E extends CoprocessorEnvironment> {
         LOG.warn("Not stopping coprocessor "+impl.getClass().getName()+
             " because not active (state="+state.toString()+")");
       }
+      synchronized (openTables) {
         // clean up any table references
         for (Table table: openTables) {
           try {
@@ -447,6 +452,7 @@ public abstract class CoprocessorHost<E extends CoprocessorEnvironment> {
           }
         }
       }
+    }
 
     @Override
     public Coprocessor getInstance() {

hbase-server/src/main/java/org/apache/hadoop/hbase/executor/EventHandler.java

@@ -97,6 +97,7 @@ public abstract class EventHandler implements Runnable, Comparable<Runnable> {
     return this;
   }
 
+  @Override
   public void run() {
     TraceScope chunk = Trace.startSpan(this.getClass().getSimpleName(), parent);
     try {
@@ -183,6 +184,10 @@ public abstract class EventHandler implements Runnable, Comparable<Runnable> {
    * @param t Throwable object
    */
   protected void handleException(Throwable t) {
-    LOG.error("Caught throwable while processing event " + eventType, t);
+    String msg = "Caught throwable while processing event " + eventType;
+    LOG.error(msg, t);
+    if (server != null) {
+      server.abort(msg, t);
+    }
   }
 }

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/handler/RegionReplicaFlushHandler.java

@@ -80,10 +80,8 @@ public class RegionReplicaFlushHandler extends EventHandler {
 
   @Override
   protected void handleException(Throwable t) {
-    super.handleException(t);
-
     if (t instanceof InterruptedIOException || t instanceof InterruptedException) {
-      // ignore
+      LOG.error("Caught throwable while processing event " + eventType, t);
     } else if (t instanceof RuntimeException) {
       server.abort("ServerAborting because a runtime exception was thrown", t);
     } else {

hbase-server/src/test/java/org/apache/hadoop/hbase/executor/TestExecutorService.java

@@ -19,8 +19,6 @@
 package org.apache.hadoop.hbase.executor;
 
 import static org.junit.Assert.*;
-import static org.junit.Assert.assertEquals;
-
 import java.io.IOException;
 import java.io.StringWriter;
 import java.util.concurrent.ThreadPoolExecutor;
@@ -29,7 +27,9 @@ import java.util.concurrent.atomic.AtomicInteger;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hbase.*;
+import org.apache.hadoop.hbase.Waiter.Predicate;
 import org.apache.hadoop.hbase.executor.ExecutorService.Executor;
 import org.apache.hadoop.hbase.executor.ExecutorService.ExecutorStatus;
 import org.apache.hadoop.hbase.testclassification.MiscTests;
@@ -173,5 +173,38 @@ public class TestExecutorService {
     }
   }
 
+  @Test
+  public void testAborting() throws Exception {
+    final Configuration conf = HBaseConfiguration.create();
+    final Server server = mock(Server.class);
+    when(server.getConfiguration()).thenReturn(conf);
+
+    ExecutorService executorService = new ExecutorService("unit_test");
+    executorService.startExecutorService(
+      ExecutorType.MASTER_SERVER_OPERATIONS, 1);
+
+
+    executorService.submit(new EventHandler(server, EventType.M_SERVER_SHUTDOWN) {
+      @Override
+      public void process() throws IOException {
+        throw new RuntimeException("Should cause abort");
+      }
+    });
+
+    Waiter.waitFor(conf, 30000, new Predicate<Exception>() {
+      @Override
+      public boolean evaluate() throws Exception {
+        try {
+          verify(server, times(1)).abort(anyString(), (Throwable) anyObject());
+          return true;
+        } catch (Throwable t) {
+          return false;
+        }
+      }
+    });
+
+    executorService.shutdown();
+  }
+
 }