How Do I Detect When a Client Thread Exits?

Here’s an interesting library writer’s dilemma. In my library (in my case EasyNetQ) I’m assigning thread local resources. So when a client creates a new thread and then calls certain methods on my library new resources get created. In the case of EasyNetQ a new channel to the RabbitMQ server is created when the client calls ‘Publish’ on a new thread. I want to be able to detect when the client thread exits so that I can clean up the resources (channels).

The only way of doing this I’ve come up with is to create a new ‘watcher’ thread that simply blocks on a Join call to the client thread. Here a simple demonstration:

First my ‘library’. It grabs the client thread and then creates a new thread which blocks on ‘Join’:

public class Library
{
    public void StartSomething()
    {
        Console.WriteLine("Library says: StartSomething called");

        var clientThread = Thread.CurrentThread;
        var exitMonitorThread = new Thread(() =>
        {
            clientThread.Join();
            Console.WriteLine("Libaray says: Client thread existed");
        });

        exitMonitorThread.Start();
    }
}

Here’s a client that uses my library. It creates a new thread and then calls my library’s StartSomething method:

public class Client
{
    private readonly Library library;

    public Client(Library library)
    {
        this.library = library;
    }

    public void DoWorkInAThread()
    {
        var thread = new Thread(() =>
        {
            library.StartSomething();
            Thread.Sleep(10);
            Console.WriteLine("Client thread says: I'm done");
        });
        thread.Start();
    }
}

When I run the client like this:

var client = new Client(new Library());

client.DoWorkInAThread();

// give the client thread time to complete
Thread.Sleep(100);

I get this output:

Library says: StartSomething called