I want to discover printers on worker thread . My end goal it to do print operation explicitly on worker thread. In UIkit, UIPrintInteractionController can send the printing job to printer in two ways: , Presenting the printing user interface(using present() func , which can work only with main thread) Printing directly to a printer(using print() func , in which we can pass UIPrinter() object containing information about the printer and it can work with worker thread). Using UIPrinterPickerController , which works on main thread , i can get list of printer . And then do the printing to that printer using method to of UIPrintInteractionController's method 2 of printing from worker thread . But i want whole printing to be done on worker thread. By using cups i want to discover the printers using worker thread , so that whole print operation in my application can happen on worker thread.