HADOOP-10475. Merge change r1585888 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1585889 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -47,6 +47,9 @@ Release 2.5.0 - UNRELEASED
     HADOOP-10468. TestMetricsSystemImpl.testMultiThreadedPublish fails
     intermediately. (wheat9)
 
+    HADOOP-10475. ConcurrentModificationException in
+    AbstractDelegationTokenSelector.selectToken(). (jing9)
+
 Release 2.4.1 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/UserGroupInformation.java

@@ -18,6 +18,7 @@
 package org.apache.hadoop.security;
 
 import static org.apache.hadoop.fs.CommonConfigurationKeys.HADOOP_USER_GROUP_METRICS_PERCENTILES_INTERVALS;
+import static org.apache.hadoop.util.PlatformName.IBM_JAVA;
 
 import java.io.File;
 import java.io.IOException;
@@ -28,6 +29,7 @@ import java.security.Principal;
 import java.security.PrivilegedAction;
 import java.security.PrivilegedActionException;
 import java.security.PrivilegedExceptionAction;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
@@ -43,9 +45,9 @@ import javax.security.auth.kerberos.KerberosKey;
 import javax.security.auth.kerberos.KerberosPrincipal;
 import javax.security.auth.kerberos.KerberosTicket;
 import javax.security.auth.login.AppConfigurationEntry;
+import javax.security.auth.login.AppConfigurationEntry.LoginModuleControlFlag;
 import javax.security.auth.login.LoginContext;
 import javax.security.auth.login.LoginException;
-import javax.security.auth.login.AppConfigurationEntry.LoginModuleControlFlag;
 import javax.security.auth.spi.LoginModule;
 
 import org.apache.commons.logging.Log;
@@ -66,7 +68,6 @@ import org.apache.hadoop.security.token.Token;
 import org.apache.hadoop.security.token.TokenIdentifier;
 import org.apache.hadoop.util.Shell;
 import org.apache.hadoop.util.Time;
-import static org.apache.hadoop.util.PlatformName.IBM_JAVA;
 
 import com.google.common.annotations.VisibleForTesting;
 
@@ -1366,7 +1367,7 @@ public class UserGroupInformation {
   public synchronized
   Collection<Token<? extends TokenIdentifier>> getTokens() {
     return Collections.unmodifiableCollection(
-        getCredentialsInternal().getAllTokens());
+        new ArrayList<Token<?>>(getCredentialsInternal().getAllTokens()));
   }
 
   /**