title: Haskell lightweight threads overhead and use on multicores
body: <p>I've been reading the "Real World Haskell" book, the chapter on concurrency and parallelism. My question is as follows:</p>
  
  <ul>
  <li><p>Since Haskell threads are really just multiple "virtual" threads inside one "real" OS-thread, does this mean that creating a lot of them (like 1000) will not have a drastic impact on performance? I.e., can we say that the overhead incurred from creating a Haskell thread with <code>forkIO</code> is (almost) negligible? Please bring pactical examples if possible.</p></li>
  <li><p>Doesn't the concept of lightweight threads prevent us from using the benefints of multicore architectures? As I understand, it is not possible for two Haskell threads to execute concurrently on two separate cores, because they are really one single thread from the operating system's point of view. Or does the Haskell runtime do some clever tricks to ensure that multiple CPU's can be made use of? </p></li>
  </ul>