[HADOOP-10487] Racy code in UserGroupInformation#ensureInitialized()

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Assignee: Haohui Mai
• Reporter: Haohui Mai
• Created: 10/Apr/14 00:55
• Updated: 14/Apr/14 21:22

Description

UserGroupInformation#ensureInitialized() uses the double-check-locking pattern to reduce the synchronization cost:

  private static void ensureInitialized() {
    if (conf == null) {
      synchronized(UserGroupInformation.class) {
        if (conf == null) { // someone might have beat us
          initialize(new Configuration(), false);
        }
      }
    }
  }

As tlipcon pointed out in the original jira (HADOOP-9748). This pattern is incorrect. Please see more details in http://en.wikipedia.org/wiki/Double-checked_locking and http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html

This jira proposes to use the static class holder pattern to do it correctly.

Issue Links

• is broken by: HADOOP-9748 Reduce blocking on UGI.ensureInitialized