C# thread does not set variable value of another class?

Question

here is my testing code:

  class Program
{
    static void Main(string[] args)
    {
        new Thread(delegate() { runThread(); }).Start();

        Console.WriteLine(Global.test);
        Console.ReadKey();
    }
    private static void runThread()
    {
        Console.WriteLine("this is run thread");
        Global.test = "this is test from thread";

        Console.WriteLine(Global.test);
    }
}
public class Global
{

    public static string testV { get; set; }
}

I want to be able to set "testV" value with a thread. it looks like Thread does set value, but when retrieving testV value from main method, it gives nothing. why is that?

The reading from the main thread probably occurs before the other thread had a chance to write the value — vc 74, May 30 '13 at 07:28

score 4 · Accepted Answer · answered May 30 '13 at 07:28

4

There is no guarantee that that Global.test has been set by the time your main thread calls WriteLine. To see the effects, you could try sleeping for a little bit before writing it out, to prove the other thread has modified it.

Also, it's worth noting that the global static testV is not thread-safe and so undefined behaviour is in your future.

answered May 30 '13 at 07:28

Moo-Juice

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@user1225072, see: http://stackoverflow.com/questions/434890/is-a-string-property-itself-threadsafe – Moo-Juice May 30 '13 at 07:39

score 1 · Answer 2 · answered May 30 '13 at 07:29

In your particular case Console.WriteLine(Global.test); runs earlier, than runThread. The simplest way is to use Join:

var thread = new Thread(delegate() { runThread(); }).Start();
thread.Join();

Console.WriteLine(Global.test);

But this is not for production code, definitely (then same is true for manual thread creation too).

C# thread does not set variable value of another class?

2 Answers2