Neil Mitchell wrote: > > I guess the "nested calls to parallel_" bit is the part of the spec > that makes everything much harder! > > Thanks > > Neil
Yes. Much more annoying. But the problem here is generic. To avoid it you must never allow all thread to block at once. The parallel_ function is such a job, so you solved this with the 'idempotent' trick. You solution works by blocking all but 1 thread. 1a) Some worker thread 1 executes parallel_ with some jobs 1b) These get submitted the work queue 'chan' 1c) worker thread 1 starts on those same jobs, ignoring the queue 1d) worker thread 1 reaches the job being processed by thread 2 1e) worker thread 1 blocks until the jobs is finished in modifyMVar 2a) Worker thread 2 grabs a job posted by thread 1, that calls parallel_ 2b) This batch of jobs gets submitted to the work queue 'chan' 2c) worker thread 2 starts on those same jobs, ignoring the queue 1d) worker thread 2 reaches the job being processed by thread 3 1e) worker thread 2 blocks until the jobs is finished in modifyMVar 3...4...5... And now only 1 thread is still working, and it has to work in series. I think I can fix this... _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe