|Perl: the Markov chain saw|
Re: [OT]: threading recursive subroutines.by ikegami (Pope)
|on Feb 02, 2011 at 19:58 UTC||Need Help??|
Good question! I've been working on it to see what the real issue is. I don't have an answer for you; I'm just documenting what I've found for everyone's benefit.
First, I presume that "inherently recursive" means "cannot be rewritten to be tail-recursive". Fibonacci is an example of an inherently recursive algorithm.
At face value, it's quite easy to make it threaded:
But what if you wanted to limit the number of threads (perhaps to limit overhead)? One solution would be to have a pool of threads and to use them if available.
(The above assumes closures can be shared, but it can be rewritten to not use closures.)
When implementing async_maybe (and the get of the object it returns), one must be extra careful to avoid the situation where a thread is waiting to have it's result collected.
But what if you want a worker model (perhaps to distribute the work to other machines)? Now, that's hard. One would need some kind of a callback system.
The TODO item is hard to do cleanly. And of course, I'm still using closures even though I think that's not an option for threads threads. Rewriting to avoid closures will likely make the code even longer.