Queuer is a queue manager, built on top of OperationQueue and Dispatch (aka GCD).
qualityOfService property on Queuer classinit function on Queuer class with maxConcurrentOperationCount and qualityOfService properties, both with a default value, so no changes are requiredConcurrentOperation is subclassable with open instead of public Access Control #2
ConcurrentOperation to create asynchronous operationsQueuer to handle a shared queue or create a custom oneRequestOperation to create network request operationsSemaphore to create a Dispath semaphoreSynchronousOperation to create synchronous operations