Simple utility for executing synchronous code in concurrent read/write blocks. Thanks to "Mastering Grand Central Dispatch" from WWDC 2011: https://developer.apple.com/videos/wwdc/2011/?id=210

RWSync.swift

/// RWSync provides methods for executing read/write blocks through the Grand Central Dispatch.
/// Multiple reads may execute concurrently, but a write will block all other executions in the queue.
class RWSync {

	private let queue: dispatch_queue_t

	/// Instantiates RWSync with a new concurrent queue.
	init() {
		let queueName = "rwsync.\(mach_absolute_time())"
		self.queue = dispatch_queue_create(queueName, DISPATCH_QUEUE_CONCURRENT)
	}

	func readAsync(cb: () -> ()) {
		dispatch_async(queue, cb)
	}

	func readAsyncMain(cb: () -> ()) {
		dispatch_async(queue) {
			dispatch_sync(dispatch_get_main_queue(), cb)
		}
	}

	func writeAsync(cb: () -> ()) {
		dispatch_barrier_async(queue, cb)
	}

}