[YARN-2945] FSLeafQueue#assignContainer - document the reason for using both write and read locks

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.7.0
• Hadoop Flags: Reviewed
• Assignee: Tsuyoshi Ozawa
• Reporter: Tsuyoshi Ozawa
• Created: 10/Dec/14 05:25
• Updated: 31/Aug/15 06:59
• Resolved: 17/Dec/14 20:04

Description

After YARN-2910, assignContainer hold WriteLock while sorting and ReadLock while referencing runnableApps. This can cause interrupted assignment of containers regardless of the policy.

    writeLock.lock();
    try {
      Collections.sort(runnableApps, comparator);
    } finally {
      writeLock.unlock();
    }
    readLock.lock();
    try {
      for (FSAppAttempt sched : runnableApps) {
        if (SchedulerAppUtils.isBlacklisted(sched, node, LOG)) {
          continue;
        }

        assigned = sched.assignContainer(node);
        if (!assigned.equals(Resources.none())) {
          break;
        }
       }
    } finally {
      readLock.unlock();
    }