Calling a code from one dispatch queue to run in another - swift

Question

I am running a CBPeripheralManager on a global dispatch queue with high priority (it's one of the initialization options). From that queue I create a dispatch timer to perform a repeated task on a custom serial queue. When that repeated task finishes, I call a member function from a dispatch_async block who specifies the global queue again.
To sum up, I'm trying to field callbacks to delegate functions on the global dispatch queue. Then calling a repeated, timed task within a custom serial queue. Finally, I want to call a function from within the serial queue to run back on the global queue.
Is that final function running outside of the serial queue, in the global queue? The dispatch_asyn for the global queue is contained within the serial queue block.

Answer 1

Your code is like the following, right?
let priority = DISPATCH_QUEUE_PRIORITY_HIGH
let globalQueue = dispatch_get_global_queue(priority, 0)
dispatch_async(globalQueue) {
//
// This block is invoked on globalQueue
// do CBPeripheralManager task
//
let serialQueue = dispatch_queue_create("custom", nil)
let timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, serialQueue)
// set timer
dispatch_source_set_event_handler(timer) {
//
// This block is invoked on serialQueue
// do task
//
if finishedRepeatedTasks {
dispatch_async(globalQueue) {
// (A)
// This block is invoked on globalQueue
// call a member function
//
}
}
}
dispatch_resume(timer)
}
And you mean (A) block call a member function was invoked on Global Queue?
Yes.