On Oct 23, 2010, at 2:57 PM, Claude Heiland-Allen wrote: On 23/10/10 17:42, Gregory Crosswhite wrote: On 10/23/10 7:54 AM, John Lato wrote: On Fri, Oct 22, 2010 at 6:16 PM, Bulat Ziganshin mailto:bulat.ziganshin@gmail.com> wrote: Hello John, Monday, October 18, 2010, 8:15:42 PM, you wrote:

If anyone is listening, I would very much like for there to be a mechanism by which external functions can be called "unsafe"-ly, but without blocking all other Haskell threads. I have code that does this:

+RTS -N2 This doesn't work, which was why the OP asked in the first place. When a thread calls an unsafe foreign function, it blocks everything until that function returns. Is that true? The last time we discussed this in Haskell Cafe the conclusion I drew from the discussion was that unsafe foreign functions block the current thread but not any other thread. The conclusion I drew was that "unsafe" foreign functions block the current "capability" (OS thread) and any "threads" (Haskell forkIO etc) currently scheduled on that capability, but other capabilities and threads continue executing as normal. I haven't tested it recently, but I think that is mostly correct except that an unsafe call will also prevent major collections, which will eventually tie up the rest of the capabilities as well.