title: What race conditions and consequences will it be if thread-unsafe collection is used
body: <p>I have a general question that I cannot quite understand. </p>
  
  <p>What race conditions and consequences will it be if thread-unsafe collection is used?</p>
  
  <p>For example, java.util.HashSet is not thread safe. So what are the kind of race conditions and consequences? Could someone list these and provide some detailed explanation?</p>
  
  <p>Thank you.</p>