Console.ReadLine and other read methods block the current thread until the user enters input. Sometimes you need to cancel the read operation when a condition is met, such as after a timeout or in response to an event.
Windows provides a function to cancel an I/O request: CancelIoEx. To use it, you need the handle of the I/O stream. In this case, it is the console input stream handle, which you can obtain with GetStdHandle using the STD_INPUT_HANDLE constant. Combining these two functions makes it straightforward to cancel a pending read. Once canceled, Console.Read throws an exception that you need to handle. Depending on the read method used, catch either InvalidOperationException or OperationCanceledException.
The following code starts a 10-second timer and calls Console.Read. If the user does not enter anything in time, the timer cancels the I/O request:
C#
class Program
{
const int STD_INPUT_HANDLE = -10;
[DllImport("kernel32.dll", SetLastError = true)]
internal static extern IntPtr GetStdHandle(int nStdHandle);
[DllImport("kernel32.dll", SetLastError = true)]
static extern bool CancelIoEx(IntPtr handle, IntPtr lpOverlapped);
static void Main(string[] args)
{
// Start the timeout
var read = false;
Task.Delay(10000).ContinueWith(_ =>
{
if (!read)
{
// Timeout => cancel the console read
var handle = GetStdHandle(STD_INPUT_HANDLE);
CancelIoEx(handle, IntPtr.Zero);
}
});
try
{
// Start reading from the console
Console.WriteLine("Do you want to continue [Y/n] (10 seconds remaining):");
var key = Console.ReadKey();
read = true;
Console.WriteLine("Key read");
}
// Handle the exception when the operation is canceled
catch (InvalidOperationException)
{
Console.WriteLine("Operation canceled");
}
catch (OperationCanceledException)
{
Console.WriteLine("Operation canceled");
}
}
}
Documentation:
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