doMC vs doSNOW vs doSMP vs doMPI: why aren't the various parallel backends for 'foreach' functionally equivalent?

Question

I\'ve got a few test pieces of code that I\'ve been running on various machines, always with the same results. I thought the philosophy behind the various do... packages wa

Answer 1

doMC forks the current R process so it inherits all the existing variables. All the other do backends only pass on explicitly requested variables. Unfortunately I didn't realise that, and only tested with doMC - this is something I hope to fix in the next version of plyr.