protected TezTaskAttemptID getTaskAttemptId(Object task) {
    // TODO: why does Tez API use "Object" for this?
    if (task instanceof TaskAttempt) {
      return ((TaskAttempt)task).getTaskAttemptID();
    }
    throw new AssertionError("LLAP plugin can only schedule task attempts");
  }
The difference between this and getTotalResources() is that this only gives currently free
resource instances, while the other lists all the instances that may become available in a
while.
llap-tez/src/java/org/apache/hadoop/hive/llap/tezplugins/LlapTaskSchedulerService.java