How do I assert that the code is running in the main thread?

Question

This doesn't work:

Debug.Assert(Thread.CurrentThread.Name == "Main Thread"); //doesn't work
                     //name is null despite name
                     //in debugger being "Main Thread"

This does work:

Debug.Assert(Thread.CurrentThread.ManagedThreadId == 1);

But I was just wondering:

a) Is ManagedThreadId guaranteed to be 1 for the Main Thread?
b) Is there a better way of doing this? Via Attribute would be neatest I feed.

I'm working on a Silverlight project, I haven't tagged as such as I don't know it's relevant, but please comment if you belive there is a difference between Silverlight and other .net runtimes.

First, what do you mean by "Main Thread"? The first to be created by the runtime? — user703016, Oct 24 '12 at 11:45
Possible duplicate of http://stackoverflow.com/questions/2374451/how-to-tell-if-a-thread-is-the-main-thread-in-c-sharp — CodeZombie, Oct 24 '12 at 11:50
@Cicada Probably, it's the name shown in the debugger in the Threads window. It might say something else in French. — weston, Oct 24 '12 at 11:51

score 2 · Answer 1 · answered Oct 24 '12 at 11:45

Thread.CurrentThread.Name only works if the name was set. My guess is the debugger provides a default name. Can you set the name of the thread (at creation, or as soon as you hit main, perhaps)? This way you can check the assertion.

Something like:

static void Main()
{
    // Check whether the thread has previously been named 
    // to avoid a possible InvalidOperationException. 
    if(Thread.CurrentThread.Name == null)
    {
        Thread.CurrentThread.Name = "MainThread";
    }
}

See: http://msdn.microsoft.com/en-us/library/system.threading.thread.name.aspx

score 1 · Accepted Answer · answered Oct 24 '12 at 12:05

1

Put this code in your entry method of an application -

static int mainThreadId;

// In Main method:
mainThreadId = System.Threading.Thread.CurrentThread.ManagedThreadId;

// If called in the non main thread, will return false;
public static bool IsMainThread
{
    get
    {
       return System.Threading.Thread.CurrentThread.ManagedThreadId
                                                == mainThreadId;
    }
}

answered Oct 24 '12 at 12:05

Rohit Vats

79,502
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This answer is "copied" from answer given by Zach Johnson here (link below) 2 years before your answer-date! What a "coincidence". Check it out: https://stackoverflow.com/questions/2374451/how-to-tell-if-a-thread-is-the-main-thread-in-c-sharp – Gsv Jul 20 '17 at 02:21

score 0 · Answer 3 · answered Oct 24 '12 at 11:44

0

Check the IsBackground property.

This might not be a perfect solution as other threads can run as foreground threads, but it might be sufficient enough.

answered Oct 24 '12 at 11:44

CodeZombie

5,367
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From the documentation on MSDN it appears threads other than the main thread could have the 'IsBackground' set to false: [link](http://msdn.microsoft.com/en-us/library/system.threading.thread.isbackground.aspx) – SpruceMoose Oct 24 '12 at 11:51

How do I assert that the code is running in the main thread?

3 Answers3

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