title: Windows Workflow Foundation equivalent of "lock"
body: <p>I have a class that inherits from <code>SequentialWorkflowActivity</code>, which can be executed simultaneously in multiple threads, and I need to make sure that part of the activity is  </p>
  
  <ul>
  <li>never interrupted  </li>
  <li>never executed across multiple threads  </li>
  </ul>
  
  <p>How can I do this in a WWF custom activity?</p>