What is the mutator?

[Jason Dusek]

  I've been reading a little about GC latency and have run
  across statements like this:

    One solution to the GC synchronisation problem would be to
    implement a concurrent garbage collector. Typically,
    however, concurrent GC adds some overhead to the mutator,
    since it must synchronise with the collector.some thunks are
    never “black-holed”, so giving a potential performance win.
    Unfortunately, in the parallel setting, it substantially
    enlarges the time window in which two or more duplicate
    threads might evaluate the same think, and thus

     -- Comparing and Optimising Parallel Haskell Implementations
        for Multicore Machines

  What is the mutator?

--
Jason Dusek