MacOS Cocoa - keep dock icon open when all windows are closed - swift

Question

my application is a listener service that is normally idle, waiting for incoming messages over the network, or for instructions from the user via the Dock icon menus.
however something keeps closing or hiding the Dock icon, unless i keep a window open.
i am working in XCode Swift, with Cocoa with Storyboards, and am developing for MacOS 10.13
i started a new project as above, and edited AppDelegate.swift as follows:
#NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {
func applicationDidFinishLaunching(_ aNotification: Notification) {
print( "app did finish launching" )
// Insert code here to initialize your application
for window in NSApp.windows {
print( window.debugDescription )
window.close()
}
DispatchQueue.global(qos: .userInitiated).async {
var seconds = 0
while true {
sleep( 1 )
print( ( seconds % 2 ) == 0 ? "tick" : "tock", seconds )
seconds += 1
}
}
}
func applicationShouldTerminateAfterLastWindowClosed(_ sender: NSApplication) -> Bool {
print( "app should terminate after last window - set regular policy" )
sender.setActivationPolicy( .regular )
return false
}
}
with no other changes, the application builds and runs, closing one window, however;
1 - the dock icon vanishes as soon as the application loses focus.
2 - after about sixty seconds the application slows down, and the sleep call is taking much longer than 1 second to return.
i need to prevent both of these behaviours, from which two questions follow:
a - where does Apple document these behaviours?
b - what is the correct way to control these behaviours?
in my experience it seems that most MacOS apps stay open in the dock, even though all of their windows are closed. for example Finder, Terminal, Safari, Notes, etc, etc.
what am i not understanding?
edited - i found this answer a week ago
Mac app disappears when window is closed then another app is selected
and i added both of parameters to my application Info, however it would seem i made an error, because i checked again today, and found they were both set to YES.
setting them both to NO appears to answer my question, my application is now working properly, and i will continue to test.
thank you, very much appreciated.