dispatch_group.swift

let dispatch_group: dispatch_group_t = dispatch_group_create()

func startRequests(){
	 asyncFunctionA()
	 asyncFunctionB()
	 dispatch_group_wait(dispatch_group, DISPATCH_TIME_FOREVER) // Wait forever! or set a reasonable default for timeout
}

func alsoStartRequests(){
	 asyncFunctionA()
	 asyncFunctionB()
	 dispatch_group_notify(dispatch_group, dispatch_get_main_queue()) { 
            // Single callback that is executed after all tasks are complete.
            if (self.errorA != nil) || (self.errorB != nil) {
            	//Handle error
            	return
            }
            self.processResponse(self.responseA, self.responseB)
     	}
}

func asyncFunctionA(){
	let urlRequest: NSURLRequest = ...
	dispatch_group_enter(dispatch_group)
	let task = self.session?.dataTaskWithRequest(urlRequest, completionHandler: {
  	(data:NSData?, response:NSURLResponse?, error:NSError?) in
  		self.errorA = error
  		self.responseA = response
		dispatch_group_leave(self.dispatch_group)
    	})
}

func asyncFunctionB(){
	let urlRequest: NSURLRequest = ...
	dispatch_group_enter(dispatch_group)
	let task = self.session?.dataTaskWithRequest(urlRequest, completionHandler: {
  	(data:NSData?, response:NSURLResponse?, error:NSError?) in
  		self.errorB = error
  		self.responseB = response
		dispatch_group_leave(self.dispatch_group)
    	})
}