We can exit from console application using ctrl + c usually on windows. I want to exit from the application using ctrl + x also. Is there a optimal way to do this?
One solution I can think of using the code similar to which is mentioned in this link.
How to achieve this?
It would be great is there if a cross platform solution, but it’s optional.
Your question is about detecting CONTROL X and your additional comment goes to the heart of the matter by asking:
[...] Where shall I write the code which I want to implement in the console application. For example like taking user input from console, then do something with that input value and write to console.
My answer, basically, is to treat them the same, polling for both CONTROL X and user input values in a single task loop but doing this strategically:
ReadKey when no character is waiting.This last point is crucial because the responsiveness is not constant but rather relies on the current activity. I have put together the following state-driven SQLite database program to demonstrate (full code is here). On the main screen, the user has only 5 choices (one of them is CONTROL X) and sampling a few times per second is plenty. If option 2 is chosen the user will enter a search term which requires a much higher sampling rate (maybe throttling to ~1 ms). The point is, we save that intensive polling for when we really need it.
What CONTROL X does
Obviously the loop will return once this is detected, but if a Task is "all there is" then what keeps the app from dropping out in the meantime? One solution is to have ConsoleApplication.Run() return a synchronization object like SemaphoreSlim and simply call Wait on it. Now the Main will not exit until CONTROL X releases the semaphore.
static void Main(string[] args)
{
ConsoleApplication.Run().Wait();
}
Under the hood, the Run method will start the process of filtering for user input by calling
Task.Run(() => filterKeyboardMessages());
Where the code goes
The activities are determined by the state. For this particular app, it is one of:
enum ConsoleState{ Menu, NewNote, SearchNotes, RecordsShown, }
This in turn is determined by user input. Every keystroke passes through this filter, where simplified outline in filterKeyboardMessages might be something like this.
while (true)
{
while (tryGetConsoleKey(out ConsoleKeyInfo keyInfo))
{
// C O N T R O L X
if (keyInfo.Modifiers == ConsoleModifiers.Control)
{
switch (keyInfo.Key)
{
case ConsoleKey.X:
// EXIT regardless of state
_running.Release();
return;
}
}
switch (CurrentState)
{
case ConsoleState.Menu:
// Only certain keys allowed
switch (keyInfo.Key)
{
case ConsoleKey.D1:
CurrentState = ConsoleState.NewNote;
break;
case ConsoleKey.D2:
CurrentState = ConsoleState.SearchNotes;
break;
case ConsoleKey.D3:
using (var cnx = new SQLiteConnection(_connectionString))
{
var sql = $"SELECT COUNT(*) FROM notes";
var count = cnx.ExecuteScalar<uint>(sql);
Console.WriteLine();
Console.WriteLine($"Database contains {count} records.");
}
break;
case ConsoleKey.D4:
using (var cnx = new SQLiteConnection(_connectionString))
{
var sql = $"DELETE FROM notes";
cnx.Execute(sql);
}
Console.WriteLine();
Console.WriteLine("Notes cleared.");
break;
}
break;
case ConsoleState.NewNote:
// Invoke editor to make a new note
break;
case ConsoleState.SearchNotes:
// - Take rapid user input keystrokes.
// - Be WAY more responsive when typing is allowed.
await Task.Delay(1);
// When ENTER is detected, perform the query
CurrentState = ConsoleState.RecordsShown;
continue;
case ConsoleState.RecordsShown:
// - The search results are now output to the screen.
switch (keyInfo.Key)
{
case ConsoleKey.Escape:
CurrentState = ConsoleState.Menu;
break;
}
break;
default:
break;
}
}
// In non-typing states, be efficient with core cycles by being less responsive.
await Task.Delay(250);
}
Sample keys without blocking
The tryGetConsoleKey is a critical utility that only blocks to read a character if it's already known to be available. The bool return value is checked with the idea that "if there's one keystroke there might be another" and uses the higher sampling rate until the buffer is depleted.
private static bool tryGetConsoleKey(out ConsoleKeyInfo key)
{
if (Console.KeyAvailable)
{
key = Console.ReadKey(intercept: true);
return true;
}
else
{
key = new ConsoleKeyInfo();
return false;
}
}
TEST
The following screenshots demonstrate the database application doing real work which at any given moment can be exited with CONTROL X.
Main view and note editor:
Make another two notes...
Now enter the search term. Something like 'tom' or 'canonical':
The record results are displayed in the RecordsShown activity:
In dotnet 6 (newest dotnet core) you can achieve it like this for instance. This would be the complete program.cs of a console application due to new using/ namespace model.
Update, explaining the code:
It doesn't really matter what version of .net you use, only mentioned it because of why you no longer would see using statements in the top of the file, which could appear odd.
So the idea is that your main program thread has to do two things, 1 start whatever your program is doing and be a root of that and now 2 listen for keyboard typing, which is has to be doing all the time so we need another thread for 1.
To do so I make a class to which i pass the cancellation token in order for the main thread doing 2 to be able to stop 1 when desired. Once instantiated, the main thread simply calls the execute method assigning it to some dummy variable to which newer versions of the language has the convenient shorthand _, the intend being that we're not going to use the return value, you could technically just not assign it to anything.
The worker in its own right then is presumed to behave a bit like a timer tick without delay at the moment, the idea is that it has to check if it needs to be cancelled at times, though in some situations once cancelling, an exception will be thrown on the thread where the cancellation token is in play, which is why i catch that exception as it's a good practice and i wanted to communicate that you may have to deal with that too. so that your program can exit on your workers periodic operation check AND if the thread gets the cancel exception which to be honest varies some but is based on the https://learn.microsoft.com/en-us/dotnet/api/system.threading.cancellationtoken.throwifcancellationrequested?view=net-6.0 setting. In case You do not want to do period tasks, but instead would like to just run sequential code, you will want to set it to throw.
var shouldContinue = true;
var c = new CancellationTokenSource();
var worker = new MyWorker(c.Token);
while (shouldContinue)
{
try
{
if (!worker.IsExecuting)
_ = worker.Execute();
ConsoleKeyInfo keyInfo = Console.ReadKey();
if(keyInfo.Modifiers.HasFlag(ConsoleModifiers.Control) && keyInfo.Key == ConsoleKey.X)
{
c.Cancel();
shouldContinue = false;
//Todo: inform the use it's bye bye time
}
} catch(Exception ex)
{
//TODO: Something loggingly
shouldContinue= false;
}
}
public class MyWorker
{
private readonly CancellationToken _cancellationToken;
private bool _isExecuting;
public MyWorker(CancellationToken cancellationToken)
{
_cancellationToken = cancellationToken;
}
public bool IsExecuting { get => _isExecuting; set => _isExecuting = value; }
public async Task Execute()
{
_isExecuting = true;
try
{
await Task.Factory.StartNew(() =>
{
while (!_cancellationToken.IsCancellationRequested)
{
//TODO: Period tasks or simply kick up procecdural what not
}
});
}
catch (OperationCanceledException)
{
//Thanks Microsoft, of cause You do not actually yourself use exceptions only for exceptional cases :-|
}
finally
{
_isExecuting = false;
}
}
}
The CTRL+C and CTRL+BREAK key combinations receive special handling by console processes. By default, when a console window has the keyboard focus, CTRL+C or CTRL+BREAK is treated as a signal (SIGINT or SIGBREAK) and not as keyboard input. By default, these signals are passed to all console processes that are attached to the console. (Detached processes are not affected. See Creation of a Console.) The system creates a new thread in each client process to handle the event. The thread raises an exception if the process is being debugged. The debugger can handle the exception or continue with the exception unhandled.
CTRL+BREAK is always treated as a signal, but an application can change the default CTRL+C behavior in two ways that prevent the handler functions from being called:
So we can do some basic things and disable CTRL+C and CTRL+Break first.
Console.TreatControlCAsInput = false;
Console.CancelKeyPress += delegate (object? sender, ConsoleCancelEventArgs e) {
e.Cancel = true;
};
Console.WriteLine("Hello, World!");
Console.ReadKey();
The next step is hook up and add ctrl+x
Console.TreatControlCAsInput = false;
Console.CancelKeyPress += delegate (object? sender, ConsoleCancelEventArgs e) {
e.Cancel = true;
};
ConsoleKeyInfo cki;
do
{
Console.WriteLine("Hello, World!");
//todo any work here
cki = Console.ReadKey(true);
} while (cki.Modifiers != ConsoleModifiers.Control && cki.Key != ConsoleKey.X);
You can try the following code :)
ConsoleKeyInfo cki;
Console.Clear();
Console.TreatControlCAsInput = true;
while (true)
{
Console.Write("Press any key, or 'CTRL' + 'X' to quit");
// Start a console read operation. Do not display the input.
cki = Console.ReadKey(true);
if ((cki.Modifiers & ConsoleModifiers.Control) == 0 || cki.Key != ConsoleKey.X) continue;
Console.Write("CTL+");
Console.WriteLine(cki.Key.ToString());
break;
}
I think your question is based on an invalid assumption. The console app doesn't handle Ctrl+C it handles the PosixSignal.SIGINT. Which is send to your console app from the operating system by pressing Ctrl+C. You can handle it as input by setting Console.TreatControlCAsInput the other signal that is used is Ctrl+Break (PosixSignal.SIGQUIT) which you cannot handle as input.
You need to handle all other keyboard input so when Ctrl+X is pressed just return.
Console.TreatControlCAsInput = true; // or false to support both
Console.Write(">");
while (true)
{
var info = Console.ReadKey();
if (info.Modifiers == ConsoleModifiers.Control && info.Key == ConsoleKey.X)
{
return;
}
}
