On http://hackage.haskell.org/trac/hackage/ticket/447, it's suggested that during parallel builds the output from child jobs simply shouldn't be displayed at all. When it comes to dealing with concurrent logging, why not have children write all log lines via queue to a master thread, then have the master flush all output associated with a job once it completes? That way the user can still see a "sequential" build, it will just seem to progress faster. P.S. If I should post questions like this on the associated task let me know. Thanks, Frank