C＃-多线程暂停

Question

Here's a code I made in C#:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace xyz
{
    class Program
    {
        Thread t1, t2;
        static void Main(string[] args)
        {
            Program go = new Program();
            go.actual();
        }
        public void actual()
        {
            t1 = new Thread(timer);
            t2 = new Thread(inputting);
            t1.Start();
            t2.Start();
        }
        public void timer()
        {
            Thread.Sleep(5000);
            t2.Abort();
            Console.WriteLine("5 seconds passed!");
        }
        public void inputting()
        {
            Console.WriteLine("Please wait 5 seconds...");
            Console.ReadKey();
        }
    }
}

Now, the problem is, when the console says "5 seconds passed!" (after aborting the t2 thread), it doesn't exit right away. This text stays there for a couple of seconds and then the console exits.

The thing is, if I press a key (of the ReadKey method) before the thread aborts, it displays the "5 seconds passed!" text and then it exits right away.

If I don't click any key, and the ReadKey method doesn't happen, it just displays the text for a couple of seconds.

Why is that? Is it a bug? And can I fix it?

Answer 1

The result you are seeing seems reasonable to me, calling Thread.Abort isn't going to somehow unblock the Console so it will still be waiting for input. Regardless, you should avoid calling Thread.Abort as there is no guarantee that it will work as expected. It's a much better approach to build cancellation support into your threads and there are various ways to do this.

Alternatively, just use the Task Parallel Library which has it all build in already.

Answer 2

From your comments I see that you basically want to timeout the Console.ReadKey call after a certain amount of time. Unfortunately, ReadKey does not have a timeout parameter. That is okay. We can wrap it in a method that does. You do not need to use any asynchronous mechanisms to accomplish this. Just use Console.KeyAvailable in a synchronous polling loop.

public static class ConsoleEx
{
  public static bool TryReadKey(TimeSpan timeout, out ConsoleKeyInfo keyinfo)
  {
    var cts = new CancellationTokenSource();
    return TryReadKey(timeout, cts.Token, out keyinfo);
  }

  public static bool TryReadKey(TimeSpan timeout, CancellationToken cancellation, out ConsoleKeyInfo keyinfo)
  {
    keyinfo = new ConsoleKeyInfo();
    DateTime latest = DateTime.UtcNow.Add(timeout);
    do
    {
        cancellation.ThrowIfCancellationRequested();
        if (Console.KeyAvailable)
        {
            keyinfo = Console.ReadKey();
            return true;
        }
        Thread.Sleep(1);
    }
    while (DateTime.UtcNow < latest);
    return false;
  }
}

And then you would use it like this.

public static void Main()
{
  ConsoleKeyInfo cki;
  if (ConsoleEx.TryReadKey(TimeSpan.FromSeconds(5), out cki))
  {
    Console.WriteLine("ReadKey returned a value.");
  }
  else
  {
    Console.WriteLine("ReadKey timed out.
  }
}