# Async

If we run an application then the code will run top-down, line by line.
If an operation takes a long time then the program will 'hang' and appear
to do nothing.
Today we want 'responsive' apps which don't 'hang' unless there is a critical fault.
Examples mainly include online/offline apps which have sensitivity to the network status.  If the app goes offline, it can either stop working or revert to an offline mode.

C#

	Main(){
		DoThisAsync();     // convention is use word 'Async' at END OF METHOD
		Console.ReadLine();  // ensure program stops and waits for async to
								complete.  Otherwise application may terminate
								before async returns.
	}

	async static void DoThisAsync(){
		await File.ReadAsync("thisfile.txt");  // marks line where aysync
		 										// operation takes place
	}

	async keyword ensures that the 'Main' method now does not WAIT for this
	method but the processing just calls the method then continues processing
	the next line of the main method.