On Mon, Jan 24, 2011 at 11:23 AM, Joshua Ballanco <jball...@gmail.com> wrote:
> Arrays in MacRuby are not inherently thread safe. However,
> "Dispatch::Queue.new" creates a serial queue. So, there is an error in that
> each invocation of the block will execute serially. If, instead, the example
> had used "Dispatch::Queue.concurrent", then there would be a potential bug,
> but the easiest way to work around that is:
> gcdq = Dispatch::Queue.concurrent
> @result = []
> @result_q = Dispatch::Queue.new('@result_assignment_queue')
> gcdq.apply(5) { |i| res = i * i; @result_q.async { @result[i] = res } }
> p @resultYes, forcing the updates to run serially rather than in parallel. The poor-man's fork/join. > There's also a mixin available in the Dispatch gem which abstracts away the > need for a serial queue for assignments by monkey-patching assignments to > all happen on a serial queue. I'm curious what you mean by this. Can you point out the code? Is it actually attempting to rewrite local variable or instance variable or array modifications in code? > For those wondering about the advantages to this technique, it's worth > noting that GCD has a much lower overhead than more traditional methods of > parallelism. That said, if the calculation for each iteration is small, this > is not a useful technique. However, if the calculation for each iteration is > long or (more likely) non-deterministic -- as in waiting for an external > call or a remote connection -- then this can be a useful technique to > continue doing useful work while letting iteration complete in the > background. I suppose it's time to explain why I'm looking into this stuff at all. I'm building a JRuby-based mimic API of the MacRuby GCD API: https://github.com/headius/jcd I started out using java.util.concurrent Executors directly, and later moved to using HawtDispatch, a libdispatch-like API. The latter has done a reasonably good job of matching the necessary dispatch_* functions in an OO API, and for the pieces that exist the wrapping job has been trivial. What I have now is a mostly-complete Queue and Object, but I'm still figuring out how to map the other libdispatch primitives to what HawtDispatch provides. The library currently is complete enough to run a fork of ControlTower I made called ChaosBazaar: http://github.com/headius/ChaosBazaar There's no real reason I shouldn't be able to support most of the MacRuby GCD APIs using just what's available on the JVM (i.e. no native or OS dependencies), which would allow those APIs to be used on any platform (and GCD client code that's not otherwise bound to MacRuby to work on JRuby without modification). I think that would be a good thing for concurrency in the Ruby world. - Charlie _______________________________________________ MacRuby-devel mailing list MacRuby-devel@lists.macosforge.org http://lists.macosforge.org/mailman/listinfo.cgi/macruby-devel
