confusion about the HBASE-11403 race condition issue

Recently, when I read the hbase source code of version 1.0.0, I found a method which I don't understand very much. That is the class AsyncProcess.java in client package, I did not understand why the code  if (tasksInProgress.get() != oldInProgress)  break exist in the private void waitForMaximumCurrentTasks(int max) method, if the  passed parameter max = 0,then it is possible that the tasksInProgress.get() > 0 but tasksInProgress.get() != oldInProgress,then the loop breaks,it is not what we want, we need all the previous jobs is done before the loop breaks,right? In the HBASE-11403, it is added to fix the race condition issue,I do not know what will cause race condition. When I click the url of the Test results, it is missing. Who can tell me why the code tasksInProgress.get() != oldInProgress shoud be added there?