title: How to use threads to replace looping a subroutine in perl/pdl
body: <p>I have a perfectly good perl subroutine written as part of a perl module. Without going into too many details, it takes a string and a short list as arguments (often taken from terminal) and spits out a value (right now, always a floating point, but this may not always be the case.)</p>
  
  <p>Right now, the list portion of my argument takes two values, say (val1,val2). I save the output of my subroutine for hundreds of different values for val1 and val2 using for loops. Each iteration takes almost a second to complete--so completing this entire process takes hours.</p>
  
  <p>I recently read of a mystical (to me) computational tool called "threading" that apparently can replace for loops with blazing fast execution time. I have been having trouble understanding what these are and do, but I imagine they have something to do with parallel computing (and I would like to have my module as optimized as possible for parallel processors.)</p>
  
  <p>If I save all the values I would like to pass to val1 as a list, say @val1 and the same for val2, how can I use these "threads" to execute my subroutine for every combination of the elements of val1 and val2?
  Also, it would be helpful to know how to generalize this procedure to a subroutine that also takes val3, val4, etc.</p>