Creating exactly N threads with Grand Central Dispatch (GCD)

Question

I know that i can execute tasks asynchronously with dispatch_async and dispatch_get_global_queue.

But how many threads dispatch_async create? What should i do to execute exactly N (no more, no less) threads with GCD, and performe some tasks on them? After execution of task i need to add new task in released thread, maybe in complitation block of previous task.

Or maybe i can control the count of threds with NSOperationQueue? I know that it has property maxConcurrentOperationCount, but it control only maximum limit of tasks. So, Can I be sure that NSOperationQueue creates no less than 8 threads, in case when i set maxConcurrentOperationCount = 8 and add 12 operations to the NSOperationQueue?

Thank you very much!

Answer 1

You should look into NSThread. It's the way to go if you need fine grain control over exactly the number of threads you want to have running.

Answer 2

Subclass NSOperation for the tasks you want to do and put them into an NSOperationQueue. You can set the number of concurrent operations on the queue.

NSOperationQueue *q = [[NSOperationQueue alloc] init];
q. maxConcurrentOperationCount = N;