title: Keeping a list of processes
body: <p>Here is my scenario: I have a function which performs operations on other processes. It performs an operation on a given process, then performs some more operations, then undoes the first operation. I would like to do this operation only once on each process.</p>
  
  <p>This leads to my question: How do I keep a list of processes to identify which ones have already been operated on and which have not? I was thinking of storing process ids, but they are recyclable. Process handles are also recyclable.</p>