Thinking about it some. I think we will need some sort of very basic thread priorities. honoring these priorities will be _manditory_ for cooperative implementations but advisory for preemptive ones that meet the fairness guarentees. priorities are sometimes needed in cooperative systems to ensure certain things get run, but the fairness guarentees of preemptive systems make them less important. Another reason to make them advisory in preemptive implementations is because they might be using OS level threads and hence not have their own scheduler to tweak priorities in. I am thinking threadSetPriority :: ThreadID -> Int -> IO () threadSetPriority = ... with a small modification to the progress guarentee saying that when threads of different priorities are runnable, one of the threads of the highest priority will be running. we should also say something about priority inheritance via MVars... but perhaps this is too complicated for the spec and should be left up to the implementations (or just make it always advisory). let me know what y'all think. John -- John Meacham - ⑆repetae.net⑆john⑈