I'm trying to work out in my head the best way to structure a Cocoa app that's essentially a concurrent download manager. There's a server the app talks to, the user makes a big list of things to pull down, and the app processes that list. (It's not using HTTP or FTP, so I can't use the URL-loading system; I'll be talking across socket connections.)
This is basically the classic producer-consumer pattern. The trick is that the number of consumers is fixed, and they're persistent. The server sets a strict limit on the number of simultaneous connections that can be open (though usually at least two), and opening new connections is expensive, so in an ideal world, the same N connections are open for the lifetime of the app. I've looked over the Apple's Concurrency Programming Guide (http://developer.apple.com/mac/library/documentation/General/Conceptual/ConcurrencyProgrammingGuide/Introduction/Introduction.html), and done some searching around on web and Stack Overflow, but not finding a lot of information that seems directly applicable, because of those constraints. One way to approach this might be to create N threads, each of which would "own" a connection, and wait on the request queue, blocking if it's empty. Since the number of connections will never be huge, this is not unreasonable in terms of actual system overhead. But conceptually, it seems like Cocoa must offer a more elegant solution. It seems like I could use an NSOperationQueue, and call setMaxConcurrentOperationCount: with the number of connections. Then I just toss the download requests into that queue. But I'm not sure, in that case, how to manage the connections themselves. (Just put them on a stack, and rely on the queue to ensure I don't over/under-run? Throw in a dispatch semaphore along with the stack?) I'd been thinking that Grand Central Dispatch might open up some other ways of tackling this, but at first blush, it doesn't seem like it. GCD's flagship ability to dynamically scale concurrency (mentioned, for example, in Apple's guide's recommendations on Changing Producer-Consumer Implementations) doesn't actually help me. But I've just scratched the surface of reading about it. Can anyone recommend other lines of inquiry? Or good examples of this kind of concurrent operation? Sixten _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
