I have a console app in which I want to give the user x seconds to respond to the prompt. If no input is made after a certain period of time, program logic should continue. We assume a timeout means empty response.
What is the most straightforward way of approaching this?
I'm surprised to learn that after 5 years, all of the answers still suffer from one or more of the following problems:
I believe my solution will solve the original problem without suffering from any of the above problems:
class Reader {
private static Thread inputThread;
private static AutoResetEvent getInput, gotInput;
private static string input;
static Reader() {
getInput = new AutoResetEvent(false);
gotInput = new AutoResetEvent(false);
inputThread = new Thread(reader);
inputThread.IsBackground = true;
inputThread.Start();
}
private static void reader() {
while (true) {
getInput.WaitOne();
input = Console.ReadLine();
gotInput.Set();
}
}
// omit the parameter to read a line without a timeout
public static string ReadLine(int timeOutMillisecs = Timeout.Infinite) {
getInput.Set();
bool success = gotInput.WaitOne(timeOutMillisecs);
if (success)
return input;
else
throw new TimeoutException("User did not provide input within the timelimit.");
}
}
Calling is, of course, very easy:
try {
Console.WriteLine("Please enter your name within the next 5 seconds.");
string name = Reader.ReadLine(5000);
Console.WriteLine("Hello, {0}!", name);
} catch (TimeoutException) {
Console.WriteLine("Sorry, you waited too long.");
}
Alternatively, you can use the TryXX(out) convention, as shmueli suggested:
public static bool TryReadLine(out string line, int timeOutMillisecs = Timeout.Infinite) {
getInput.Set();
bool success = gotInput.WaitOne(timeOutMillisecs);
if (success)
line = input;
else
line = null;
return success;
}
Which is called as follows:
Console.WriteLine("Please enter your name within the next 5 seconds.");
string name;
bool success = Reader.TryReadLine(out name, 5000);
if (!success)
Console.WriteLine("Sorry, you waited too long.");
else
Console.WriteLine("Hello, {0}!", name);
In both cases, you cannot mix calls to Reader with normal Console.ReadLine calls: if the Reader times out, there will be a hanging ReadLine call. Instead, if you want to have a normal (non-timed) ReadLine call, just use the Reader and omit the timeout, so that it defaults to an infinite timeout.
So how about those problems of the other solutions I mentioned?
The only problem that I foresee with this solution is that it is not thread-safe. However, multiple threads can't really ask the user for input at the same time, so synchronization should be happening before making a call to Reader.ReadLine anyway.
AutoResetEvents should be initialized before starting the thread. I edited the code in the post. Thanks! –
Retroversion horrible waste, but of course your signalling is superior. Also, using one blocking Console.ReadLine call in an infinite-loop in a second threat prevents the problems with lots of such calls hanging around in the background as in the other, heavily upvoted, solutions below. Thank you for sharing your code. +1 –
Introspect Console.ReadLine() call you make. You end up with a "phantom" ReadLine that needs to be completed first. –
Flipflop IsBackground property to true? –
Retroversion getInput. –
Martinelli consumerGreenLight and producerGreenLight. –
Martinelli Reader.ReadLine in time (i.e. you type "he" and then timeout happens) the incomplete input is part of subsequent Reader.ReadLine (i.e. if you type "lo" the second time, the result is "helo" instead of "lo"). –
Tobar getInput. Since the next call to Console.ReadLine() blocks anyways. I think the only need for getInput() is to save the very first call to Console.Readline() if Reader.Readline() will NEVER be called in the application llifetime. –
Blakley string ReadLine(int timeoutms)
{
ReadLineDelegate d = Console.ReadLine;
IAsyncResult result = d.BeginInvoke(null, null);
result.AsyncWaitHandle.WaitOne(timeoutms);//timeout e.g. 15000 for 15 secs
if (result.IsCompleted)
{
string resultstr = d.EndInvoke(result);
Console.WriteLine("Read: " + resultstr);
return resultstr;
}
else
{
Console.WriteLine("Timed out!");
throw new TimedoutException("Timed Out!");
}
}
delegate string ReadLineDelegate();
ReadLine you call sits there waiting for input. If you call it 100 times, it creates 100 threads which don't all go away until you hit Enter 100 times! –
Bellinger EndInvoke call on timeout cannot be solved. On the other hand, the accepted solution with one sync call in a second thread, running forever, is perfect. Thank you for your effort, but I cannot use your solution. -1 sorry –
Introspect Will this approach using Console.KeyAvailable help?
class Sample
{
public static void Main()
{
ConsoleKeyInfo cki = new ConsoleKeyInfo();
do {
Console.WriteLine("\nPress a key to display; press the 'x' key to quit.");
// Your code could perform some useful task in the following loop. However,
// for the sake of this example we'll merely pause for a quarter second.
while (Console.KeyAvailable == false)
Thread.Sleep(250); // Loop until input is entered.
cki = Console.ReadKey(true);
Console.WriteLine("You pressed the '{0}' key.", cki.Key);
} while(cki.Key != ConsoleKey.X);
}
}
KeyAvailable only indicates that the user has started typing input to ReadLine, but we need an event on pressing Enter, that makes ReadLine to return. This solution only works for ReadKey, i.e., getting just one character. As this does not solve the actual question for ReadLine, I cannot use your solution. -1 sorry –
Introspect This worked for me.
ConsoleKeyInfo k = new ConsoleKeyInfo();
Console.WriteLine("Press any key in the next 5 seconds.");
for (int cnt = 5; cnt > 0; cnt--)
{
if (Console.KeyAvailable)
{
k = Console.ReadKey();
break;
}
else
{
Console.WriteLine(cnt.ToString());
System.Threading.Thread.Sleep(1000);
}
}
Console.WriteLine("The key pressed was " + k.Key);
One way or another you do need a second thread. You could use asynchronous IO to avoid declaring your own:
If the read returns data, set the event and your main thread will continue, otherwise you'll continue after the timeout.
If you're in the Main() method, you can't use await, so you'll have to use Task.WaitAny():
var task = Task.Factory.StartNew(Console.ReadLine);
var result = Task.WaitAny(new Task[] { task }, TimeSpan.FromSeconds(5)) == 0
? task.Result : string.Empty;
However, C# 7.1 introduces the possiblity to create an async Main() method, so it's better to use the Task.WhenAny() version whenever you have that option:
var task = Task.Factory.StartNew(Console.ReadLine);
var completedTask = await Task.WhenAny(task, Task.Delay(TimeSpan.FromSeconds(5)));
var result = object.ReferenceEquals(task, completedTask) ? task.Result : string.Empty;
// Wait for 'Enter' to be pressed or 5 seconds to elapse
using (Stream s = Console.OpenStandardInput())
{
ManualResetEvent stop_waiting = new ManualResetEvent(false);
s.BeginRead(new Byte[1], 0, 1, ar => stop_waiting.Set(), null);
// ...do anything else, or simply...
stop_waiting.WaitOne(5000);
// If desired, other threads could also set 'stop_waiting'
// Disposing the stream cancels the async read operation. It can be
// re-opened if needed.
}
I think you will need to make a secondary thread and poll for a key on the console. I know of no built in way to accomplish this.
Calling Console.ReadLine() in the delegate is bad because if the user doesn't hit 'enter' then that call will never return. The thread executing the delegate will be blocked until the user hits 'enter', with no way to cancel it.
Issuing a sequence of these calls will not behave as you would expect. Consider the following (using the example Console class from above):
System.Console.WriteLine("Enter your first name [John]:");
string firstName = Console.ReadLine(5, "John");
System.Console.WriteLine("Enter your last name [Doe]:");
string lastName = Console.ReadLine(5, "Doe");
The user lets the timeout expire for the first prompt, then enters a value for the second prompt. Both firstName and lastName will contain the default values. When the user hits 'enter', the first ReadLine call will complete, but the code has abandonded that call and essentially discarded the result. The second ReadLine call will continue to block, the timeout will eventually expire and the value returned will again be the default.
BTW- There is a bug in the code above. By calling waitHandle.Close() you close the event out from under the worker thread. If the user hits 'enter' after the timeout expires, the worker thread will attempt to signal the event which throws an ObjectDisposedException. The exception is thrown from the worker thread, and if you haven't setup an unhandled exception handler your process will terminate.
I struggled with this problem for 5 months before I found an solution that works perfectly in an enterprise setting.
The problem with most of the solutions so far is that they rely on something other than Console.ReadLine(), and Console.ReadLine() has a lot of advantages:
My solution is as follows:
Sample code:
InputSimulator.SimulateKeyPress(VirtualKeyCode.RETURN);
More information on this technique, including the correct technique to abort a thread that uses Console.ReadLine:
.NET call to send [enter] keystroke into the current process, which is a console app?
How to abort another thread in .NET, when said thread is executing Console.ReadLine?
I may be reading too much into the question, but I am assuming the wait would be similar to the boot menu where it waits 15 seconds unless you press a key. You could either use (1) a blocking function or (2) you could use a thread, an event, and a timer. The event would act as a 'continue' and would block until either the timer expired or a key was pressed.
Pseudo-code for (1) would be:
// Get configurable wait time
TimeSpan waitTime = TimeSpan.FromSeconds(15.0);
int configWaitTimeSec;
if (int.TryParse(ConfigManager.AppSetting["DefaultWaitTime"], out configWaitTimeSec))
waitTime = TimeSpan.FromSeconds(configWaitTimeSec);
bool keyPressed = false;
DateTime expireTime = DateTime.Now + waitTime;
// Timer and key processor
ConsoleKeyInfo cki;
// EDIT: adding a missing ! below
while (!keyPressed && (DateTime.Now < expireTime))
{
if (Console.KeyAvailable)
{
cki = Console.ReadKey(true);
// TODO: Process key
keyPressed = true;
}
Thread.Sleep(10);
}
As if there weren't already enough answers here :0), the following encapsulates into a static method @kwl's solution above (the first one).
public static string ConsoleReadLineWithTimeout(TimeSpan timeout)
{
Task<string> task = Task.Factory.StartNew(Console.ReadLine);
string result = Task.WaitAny(new Task[] { task }, timeout) == 0
? task.Result
: string.Empty;
return result;
}
Usage
static void Main()
{
Console.WriteLine("howdy");
string result = ConsoleReadLineWithTimeout(TimeSpan.FromSeconds(8.5));
Console.WriteLine("bye");
}
.NET 4 makes this incredibly simple using Tasks.
First, build your helper:
Private Function AskUser() As String
Console.Write("Answer my question: ")
Return Console.ReadLine()
End Function
Second, execute with a task and wait:
Dim askTask As Task(Of String) = New TaskFactory().StartNew(Function() AskUser())
askTask.Wait(TimeSpan.FromSeconds(30))
If Not askTask.IsCompleted Then
Console.WriteLine("User failed to respond.")
Else
Console.WriteLine(String.Format("You responded, '{0}'.", askTask.Result))
End If
There's no trying to recreate ReadLine functionality or performing other perilous hacks to get this working. Tasks let us solve the question in a very natural way.
EDIT: fixed the problem by having the actual work be done in a separate process and killing that process if it times out. See below for details. Whew!
Just gave this a run and it seemed to work nicely. My coworker had a version which used a Thread object, but I find the BeginInvoke() method of delegate types to be a bit more elegant.
namespace TimedReadLine
{
public static class Console
{
private delegate string ReadLineInvoker();
public static string ReadLine(int timeout)
{
return ReadLine(timeout, null);
}
public static string ReadLine(int timeout, string @default)
{
using (var process = new System.Diagnostics.Process
{
StartInfo =
{
FileName = "ReadLine.exe",
RedirectStandardOutput = true,
UseShellExecute = false
}
})
{
process.Start();
var rli = new ReadLineInvoker(process.StandardOutput.ReadLine);
var iar = rli.BeginInvoke(null, null);
if (!iar.AsyncWaitHandle.WaitOne(new System.TimeSpan(0, 0, timeout)))
{
process.Kill();
return @default;
}
return rli.EndInvoke(iar);
}
}
}
}
The ReadLine.exe project is a very simple one which has one class which looks like so:
namespace ReadLine
{
internal static class Program
{
private static void Main()
{
System.Console.WriteLine(System.Console.ReadLine());
}
}
}
Console.ReadLine() are blocking and will hold up input on the next request. The accepted answer is fairly close, but still has limitations. –
Tega ReadLine() in your program after calling this one. See what happens. You have to hit return TWICE to get it to go due to the single-threaded nature of the Console. It. Doesn't. Work. –
Tega I can't comment on Gulzar's post unfortunately, but here's a fuller example:
while (Console.KeyAvailable == false)
{
Thread.Sleep(250);
i++;
if (i > 3)
throw new Exception("Timedout waiting for input.");
}
input = Console.ReadLine();
My code is based entirely on the friend's answer @JSQuareD
But I needed to use Stopwatch to timer because when I finished the program with Console.ReadKey() it was still waiting for Console.ReadLine() and it generated unexpected behavior.
It WORKED PERFECTLY for me. Maintains the original Console.ReadLine ()
class Program
{
static void Main(string[] args)
{
Console.WriteLine("What is the answer? (5 secs.)");
try
{
var answer = ConsoleReadLine.ReadLine(5000);
Console.WriteLine("Answer is: {0}", answer);
}
catch
{
Console.WriteLine("No answer");
}
Console.ReadKey();
}
}
class ConsoleReadLine
{
private static string inputLast;
private static Thread inputThread = new Thread(inputThreadAction) { IsBackground = true };
private static AutoResetEvent inputGet = new AutoResetEvent(false);
private static AutoResetEvent inputGot = new AutoResetEvent(false);
static ConsoleReadLine()
{
inputThread.Start();
}
private static void inputThreadAction()
{
while (true)
{
inputGet.WaitOne();
inputLast = Console.ReadLine();
inputGot.Set();
}
}
// omit the parameter to read a line without a timeout
public static string ReadLine(int timeout = Timeout.Infinite)
{
if (timeout == Timeout.Infinite)
{
return Console.ReadLine();
}
else
{
var stopwatch = new Stopwatch();
stopwatch.Start();
while (stopwatch.ElapsedMilliseconds < timeout && !Console.KeyAvailable) ;
if (Console.KeyAvailable)
{
inputGet.Set();
inputGot.WaitOne();
return inputLast;
}
else
{
throw new TimeoutException("User did not provide input within the timelimit.");
}
}
}
}
Simple threading example to solve this
Thread readKeyThread = new Thread(ReadKeyMethod);
static ConsoleKeyInfo cki = null;
void Main()
{
readKeyThread.Start();
bool keyEntered = false;
for(int ii = 0; ii < 10; ii++)
{
Thread.Sleep(1000);
if(readKeyThread.ThreadState == ThreadState.Stopped)
keyEntered = true;
}
if(keyEntered)
{ //do your stuff for a key entered
}
}
void ReadKeyMethod()
{
cki = Console.ReadKey();
}
or a static string up top for getting an entire line.
Im my case this work fine:
public static ManualResetEvent evtToWait = new ManualResetEvent(false);
private static void ReadDataFromConsole( object state )
{
Console.WriteLine("Enter \"x\" to exit or wait for 5 seconds.");
while (Console.ReadKey().KeyChar != 'x')
{
Console.Out.WriteLine("");
Console.Out.WriteLine("Enter again!");
}
evtToWait.Set();
}
static void Main(string[] args)
{
Thread status = new Thread(ReadDataFromConsole);
status.Start();
evtToWait = new ManualResetEvent(false);
evtToWait.WaitOne(5000); // wait for evtToWait.Set() or timeOut
status.Abort(); // exit anyway
return;
}
Isn't this nice and short?
if (SpinWait.SpinUntil(() => Console.KeyAvailable, millisecondsTimeout))
{
ConsoleKeyInfo keyInfo = Console.ReadKey();
// Handle keyInfo value here...
}
This is a fuller example of Glen Slayden's solution. I happended to make this when building a test case for another problem. It uses asynchronous I/O and a manual reset event.
public static void Main() {
bool readInProgress = false;
System.IAsyncResult result = null;
var stop_waiting = new System.Threading.ManualResetEvent(false);
byte[] buffer = new byte[256];
var s = System.Console.OpenStandardInput();
while (true) {
if (!readInProgress) {
readInProgress = true;
result = s.BeginRead(buffer, 0, buffer.Length
, ar => stop_waiting.Set(), null);
}
bool signaled = true;
if (!result.IsCompleted) {
stop_waiting.Reset();
signaled = stop_waiting.WaitOne(5000);
}
else {
signaled = true;
}
if (signaled) {
readInProgress = false;
int numBytes = s.EndRead(result);
string text = System.Text.Encoding.UTF8.GetString(buffer
, 0, numBytes);
System.Console.Out.Write(string.Format(
"Thank you for typing: {0}", text));
}
else {
System.Console.Out.WriteLine("oy, type something!");
}
}
Here is safe solution which fakes console input to unblock thread after timeout. https://github.com/Igorium/ConsoleReader project provides a sample user dialog implementation.
var inputLine = ReadLine(5);
public static string ReadLine(uint timeoutSeconds, Func<uint, string> countDownMessage, uint samplingFrequencyMilliseconds)
{
if (timeoutSeconds == 0)
return null;
var timeoutMilliseconds = timeoutSeconds * 1000;
if (samplingFrequencyMilliseconds > timeoutMilliseconds)
throw new ArgumentException("Sampling frequency must not be greater then timeout!", "samplingFrequencyMilliseconds");
CancellationTokenSource cts = new CancellationTokenSource();
Task.Factory
.StartNew(() => SpinUserDialog(timeoutMilliseconds, countDownMessage, samplingFrequencyMilliseconds, cts.Token), cts.Token)
.ContinueWith(t => {
var hWnd = System.Diagnostics.Process.GetCurrentProcess().MainWindowHandle;
PostMessage(hWnd, 0x100, 0x0D, 9);
}, TaskContinuationOptions.NotOnCanceled);
var inputLine = Console.ReadLine();
cts.Cancel();
return inputLine;
}
private static void SpinUserDialog(uint countDownMilliseconds, Func<uint, string> countDownMessage, uint samplingFrequencyMilliseconds,
CancellationToken token)
{
while (countDownMilliseconds > 0)
{
token.ThrowIfCancellationRequested();
Thread.Sleep((int)samplingFrequencyMilliseconds);
countDownMilliseconds -= countDownMilliseconds > samplingFrequencyMilliseconds
? samplingFrequencyMilliseconds
: countDownMilliseconds;
}
}
[DllImport("User32.Dll", EntryPoint = "PostMessageA")]
private static extern bool PostMessage(IntPtr hWnd, uint msg, int wParam, int lParam);
I've got a solution to this using the Windows API that has some benefits over many of the solutions here:
The two main downsides:
The basic idea is that the Windows API has a function to cancel outstanding I/O requests: CancelIoEx. When you use it to cancel operations on STDIN, Console.ReadLine throws an OperationCanceledException.
So here's how you do it:
using System;
using System.Runtime.InteropServices;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleHelper
{
public static class ConsoleHelper
{
public static string ReadLine(TimeSpan timeout)
{
return ReadLine(Task.Delay(timeout));
}
public static string ReadLine(Task cancel_trigger)
{
var status = new Status();
var cancel_task = Task.Run(async () =>
{
await cancel_trigger;
status.Mutex.WaitOne();
bool io_done = status.IODone;
if (!io_done)
status.CancellationStarted = true;
status.Mutex.ReleaseMutex();
while (!status.IODone)
{
var success = CancelStdIn(out int error_code);
if (!success && error_code != 0x490) // 0x490 is what happens when you call cancel and there is not a pending I/O request
throw new Exception($"Canceling IO operation on StdIn failed with error {error_code} ({error_code:x})");
}
});
ReadLineWithStatus(out string input, out bool read_canceled);
if (!read_canceled)
{
status.Mutex.WaitOne();
bool must_wait = status.CancellationStarted;
status.IODone = true;
status.Mutex.ReleaseMutex();
if (must_wait)
cancel_task.Wait();
return input;
}
else // read_canceled == true
{
status.Mutex.WaitOne();
bool cancel_started = status.CancellationStarted;
status.IODone = true;
status.Mutex.ReleaseMutex();
if (!cancel_started)
throw new Exception("Received cancelation not triggered by this method.");
else
cancel_task.Wait();
return null;
}
}
private const int STD_INPUT_HANDLE = -10;
[DllImport("kernel32.dll", SetLastError = true)]
private static extern IntPtr GetStdHandle(int nStdHandle);
[DllImport("kernel32.dll", SetLastError = true)]
private static extern bool CancelIoEx(IntPtr handle, IntPtr lpOverlapped);
private static bool CancelStdIn(out int error_code)
{
var handle = GetStdHandle(STD_INPUT_HANDLE);
bool success = CancelIoEx(handle, IntPtr.Zero);
if (success)
{
error_code = 0;
return true;
}
else
{
var rc = Marshal.GetLastWin32Error();
error_code = rc;
return false;
}
}
private class Status
{
public Mutex Mutex = new Mutex(false);
public volatile bool IODone;
public volatile bool CancellationStarted;
}
private static void ReadLineWithStatus(out string result, out bool operation_canceled)
{
try
{
result = Console.ReadLine();
operation_canceled = false;
}
catch (OperationCanceledException)
{
result = null;
operation_canceled = true;
}
}
}
}
Avoid the temptation to simplify this, getting the threading right is pretty tricky. You need to handle all of these cases:
CancelStdIn is called before Console.ReadLine starts (this is why you need the loop in the cancel_trigger).CancelStdIn is called.CancelStdIn in response to the cancel trigger.Credits: Got the idea for CancelIoEx from a SO answer who got it from Gérald Barré's blog. However those solutions have subtle concurrency bugs.
Example implementation of Eric's post above. This particular example was used to read information that was passed to a console app via pipe:
using System;
using System.Collections.Generic;
using System.IO;
using System.Threading;
namespace PipedInfo
{
class Program
{
static void Main(string[] args)
{
StreamReader buffer = ReadPipedInfo();
Console.WriteLine(buffer.ReadToEnd());
}
#region ReadPipedInfo
public static StreamReader ReadPipedInfo()
{
//call with a default value of 5 milliseconds
return ReadPipedInfo(5);
}
public static StreamReader ReadPipedInfo(int waitTimeInMilliseconds)
{
//allocate the class we're going to callback to
ReadPipedInfoCallback callbackClass = new ReadPipedInfoCallback();
//to indicate read complete or timeout
AutoResetEvent readCompleteEvent = new AutoResetEvent(false);
//open the StdIn so that we can read against it asynchronously
Stream stdIn = Console.OpenStandardInput();
//allocate a one-byte buffer, we're going to read off the stream one byte at a time
byte[] singleByteBuffer = new byte[1];
//allocate a list of an arbitary size to store the read bytes
List<byte> byteStorage = new List<byte>(4096);
IAsyncResult asyncRead = null;
int readLength = 0; //the bytes we have successfully read
do
{
//perform the read and wait until it finishes, unless it's already finished
asyncRead = stdIn.BeginRead(singleByteBuffer, 0, singleByteBuffer.Length, new AsyncCallback(callbackClass.ReadCallback), readCompleteEvent);
if (!asyncRead.CompletedSynchronously)
readCompleteEvent.WaitOne(waitTimeInMilliseconds);
//end the async call, one way or another
//if our read succeeded we store the byte we read
if (asyncRead.IsCompleted)
{
readLength = stdIn.EndRead(asyncRead);
if (readLength > 0)
byteStorage.Add(singleByteBuffer[0]);
}
} while (asyncRead.IsCompleted && readLength > 0);
//we keep reading until we fail or read nothing
//return results, if we read zero bytes the buffer will return empty
return new StreamReader(new MemoryStream(byteStorage.ToArray(), 0, byteStorage.Count));
}
private class ReadPipedInfoCallback
{
public void ReadCallback(IAsyncResult asyncResult)
{
//pull the user-defined variable and strobe the event, the read finished successfully
AutoResetEvent readCompleteEvent = asyncResult.AsyncState as AutoResetEvent;
readCompleteEvent.Set();
}
}
#endregion ReadPipedInfo
}
}
Another cheap way to get a 2nd thread is to wrap it in a delegate.
string readline = "?";
ThreadPool.QueueUserWorkItem(
delegate
{
readline = Console.ReadLine();
}
);
do
{
Thread.Sleep(100);
} while (readline == "?");
Note that if you go down the "Console.ReadKey" route, you lose some of the cool features of ReadLine, namely:
To add a timeout, alter the while loop to suit.
Please don't hate me for adding another solution to the plethora of existing answers! This works for Console.ReadKey(), but could easily be modified to work with ReadLine(), etc.
As the "Console.Read" methods are blocking, it's necessary to "nudge" the StdIn stream to cancel the read.
Calling syntax:
ConsoleKeyInfo keyInfo;
bool keyPressed = AsyncConsole.ReadKey(500, out keyInfo);
// where 500 is the timeout
Code:
public class AsyncConsole // not thread safe
{
private static readonly Lazy<AsyncConsole> Instance =
new Lazy<AsyncConsole>();
private bool _keyPressed;
private ConsoleKeyInfo _keyInfo;
private bool DoReadKey(
int millisecondsTimeout,
out ConsoleKeyInfo keyInfo)
{
_keyPressed = false;
_keyInfo = new ConsoleKeyInfo();
Thread readKeyThread = new Thread(ReadKeyThread);
readKeyThread.IsBackground = false;
readKeyThread.Start();
Thread.Sleep(millisecondsTimeout);
if (readKeyThread.IsAlive)
{
try
{
IntPtr stdin = GetStdHandle(StdHandle.StdIn);
CloseHandle(stdin);
readKeyThread.Join();
}
catch { }
}
readKeyThread = null;
keyInfo = _keyInfo;
return _keyPressed;
}
private void ReadKeyThread()
{
try
{
_keyInfo = Console.ReadKey();
_keyPressed = true;
}
catch (InvalidOperationException) { }
}
public static bool ReadKey(
int millisecondsTimeout,
out ConsoleKeyInfo keyInfo)
{
return Instance.Value.DoReadKey(millisecondsTimeout, out keyInfo);
}
private enum StdHandle { StdIn = -10, StdOut = -11, StdErr = -12 };
[DllImport("kernel32.dll")]
private static extern IntPtr GetStdHandle(StdHandle std);
[DllImport("kernel32.dll")]
private static extern bool CloseHandle(IntPtr hdl);
}
Here is a solution that uses Console.KeyAvailable. These are blocking calls, but it should be fairly trivial to call them asynchronously via the TPL if desired. I used the standard cancellation mechanisms to make it easy to wire in with the Task Asynchronous Pattern and all that good stuff.
public static class ConsoleEx
{
public static string ReadLine(TimeSpan timeout)
{
var cts = new CancellationTokenSource();
return ReadLine(timeout, cts.Token);
}
public static string ReadLine(TimeSpan timeout, CancellationToken cancellation)
{
string line = "";
DateTime latest = DateTime.UtcNow.Add(timeout);
do
{
cancellation.ThrowIfCancellationRequested();
if (Console.KeyAvailable)
{
ConsoleKeyInfo cki = Console.ReadKey();
if (cki.Key == ConsoleKey.Enter)
{
return line;
}
else
{
line += cki.KeyChar;
}
}
Thread.Sleep(1);
}
while (DateTime.UtcNow < latest);
return null;
}
}
There are some disadvantages with this.
ReadLine provides (up/down arrow scrolling, etc.).Ended up here because a duplicate question was asked. I came up with the following solution which looks straightforward. I am sure it has some drawbacks I missed.
static void Main(string[] args)
{
Console.WriteLine("Hit q to continue or wait 10 seconds.");
Task task = Task.Factory.StartNew(() => loop());
Console.WriteLine("Started waiting");
task.Wait(10000);
Console.WriteLine("Stopped waiting");
}
static void loop()
{
while (true)
{
if ('q' == Console.ReadKey().KeyChar) break;
}
}
I came to this answer and end up doing:
/// <summary>
/// Reads Line from console with timeout.
/// </summary>
/// <exception cref="System.TimeoutException">If user does not enter line in the specified time.</exception>
/// <param name="timeout">Time to wait in milliseconds. Negative value will wait forever.</param>
/// <returns></returns>
public static string ReadLine(int timeout = -1)
{
ConsoleKeyInfo cki = new ConsoleKeyInfo();
StringBuilder sb = new StringBuilder();
// if user does not want to spesify a timeout
if (timeout < 0)
return Console.ReadLine();
int counter = 0;
while (true)
{
while (Console.KeyAvailable == false)
{
counter++;
Thread.Sleep(1);
if (counter > timeout)
throw new System.TimeoutException("Line was not entered in timeout specified");
}
cki = Console.ReadKey(false);
if (cki.Key == ConsoleKey.Enter)
{
Console.WriteLine();
return sb.ToString();
}
else
sb.Append(cki.KeyChar);
}
}
A simple example using Console.KeyAvailable:
Console.WriteLine("Press any key during the next 2 seconds...");
Thread.Sleep(2000);
if (Console.KeyAvailable)
{
Console.WriteLine("Key pressed");
}
else
{
Console.WriteLine("You were too slow");
}
Much more contemporary and Task based code would look something like this:
public string ReadLine(int timeOutMillisecs)
{
var inputBuilder = new StringBuilder();
var task = Task.Factory.StartNew(() =>
{
while (true)
{
var consoleKey = Console.ReadKey(true);
if (consoleKey.Key == ConsoleKey.Enter)
{
return inputBuilder.ToString();
}
inputBuilder.Append(consoleKey.KeyChar);
}
});
var success = task.Wait(timeOutMillisecs);
if (!success)
{
throw new TimeoutException("User did not provide input within the timelimit.");
}
return inputBuilder.ToString();
}
I had a unique situation of having a Windows Application (Windows Service). When running the program interactively Environment.IsInteractive (VS Debugger or from cmd.exe), I used AttachConsole/AllocConsole to get my stdin/stdout.
To keep the process from ending while the work was being done, the UI Thread calls Console.ReadKey(false). I wanted to cancel the waiting the UI thread was doing from another thread, so I came up with a modification to the solution by @JSquaredD.
using System;
using System.Diagnostics;
internal class PressAnyKey
{
private static Thread inputThread;
private static AutoResetEvent getInput;
private static AutoResetEvent gotInput;
private static CancellationTokenSource cancellationtoken;
static PressAnyKey()
{
// Static Constructor called when WaitOne is called (technically Cancel too, but who cares)
getInput = new AutoResetEvent(false);
gotInput = new AutoResetEvent(false);
inputThread = new Thread(ReaderThread);
inputThread.IsBackground = true;
inputThread.Name = "PressAnyKey";
inputThread.Start();
}
private static void ReaderThread()
{
while (true)
{
// ReaderThread waits until PressAnyKey is called
getInput.WaitOne();
// Get here
// Inner loop used when a caller uses PressAnyKey
while (!Console.KeyAvailable && !cancellationtoken.IsCancellationRequested)
{
Thread.Sleep(50);
}
// Release the thread that called PressAnyKey
gotInput.Set();
}
}
/// <summary>
/// Signals the thread that called WaitOne should be allowed to continue
/// </summary>
public static void Cancel()
{
// Trigger the alternate ending condition to the inner loop in ReaderThread
if(cancellationtoken== null) throw new InvalidOperationException("Must call WaitOne before Cancelling");
cancellationtoken.Cancel();
}
/// <summary>
/// Wait until a key is pressed or <see cref="Cancel"/> is called by another thread
/// </summary>
public static void WaitOne()
{
if(cancellationtoken==null || cancellationtoken.IsCancellationRequested) throw new InvalidOperationException("Must cancel a pending wait");
cancellationtoken = new CancellationTokenSource();
// Release the reader thread
getInput.Set();
// Calling thread will wait here indefiniately
// until a key is pressed, or Cancel is called
gotInput.WaitOne();
}
}
This seems to be the simplest, working solution, that doesn't use any native APIs:
static Task<string> ReadLineAsync(CancellationToken cancellation)
{
return Task.Run(() =>
{
while (!Console.KeyAvailable)
{
if (cancellation.IsCancellationRequested)
return null;
Thread.Sleep(100);
}
return Console.ReadLine();
});
}
Example usage:
static void Main(string[] args)
{
AsyncContext.Run(async () =>
{
CancellationTokenSource cancelSource = new CancellationTokenSource();
cancelSource.CancelAfter(1000);
Console.WriteLine(await ReadLineAsync(cancelSource.Token) ?? "null");
});
}
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