I too am confused by your results. Right now I have 3 speculative possibilities:

  1. Your cpu isn't a real dual-core, but rather one of those pseudo-dual core hyperthreaded things, and your OS is presenting it as if it were a true dual core.
  2. One or more of the R dlls is non-threadsafe, and they've dodged the issue by using a semaphore to serialise access.

    This seems to be the most likely explanation.

  3. There is something inherent in your implementation that is causing the threads to serialise.

    I haven't been able to spot anything from a fairly extended inspection, but there is rather too much code to comprehensively 'run it in my head'.

    Unfortunately, even if I had the data files, I would still not be able to run it here as IPC::Open2 (nor any of the alternatives), don't work worth a damn on my platform.

My best suggestion for isolating which (if any) of the above is the problem, is to log the command output of your demo run, split it into 2 and then start two manual R sessions and feed (pipe) half to each and set them both going at the same time and see how long they take.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
RIP PCW It is as I've been saying!(Audio until 20090817)

In reply to Re^5: Using threads to run multiple external processes at the same time by BrowserUk
in thread Using threads to run multiple external processes at the same time by Anonymous Monk

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