On Mon, Aug 19, 2013 at 2:08 PM, Patrick Connolly <p_conno...@slingshot.co.nz> wrote: > On Sat, 17-Aug-2013 at 05:09PM -0700, Jeff Newmiller wrote: > > > |> In most threaded multitasking environments it is not safe to > |> perform IO in multiple threads. In general you will have difficulty > |> performing IO in parallel processing so it is best to let the > |> master hand out data to worker tasks and gather results from them > |> for storage. Keep in mind that just because you have eight cores > |> for processing doesn't mean you have eight hard disks, so if your > |> problem is IO bound in single processor operation then it will also > |> be IO bound in threaded operation. > > For tasks which don't involve I/O but fail with mclapply, how does one > work out where the problem is? The handy browser() function which > allows for interactive diagnosis won't work with parallel jobs. > > What other approaches can one use? >
browser() requires I/O doesn't it? Anyways -- my rule of thumb is anything involving "the outside world" won't work so I/O covers most of it, but you also need to be aware of things like RNG (which can involve subtle IO with a global random seed if you're not aware of the concerns in the parallel package vignette). More precisely, anything that would be hard in a functional language (like Haskell) should keep you wary. Cheers, MW ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
