Handle leaks with .NET System.Threading.Thread class

Question

I've a problem that number of Handles in my app is continuously growing. I did the debugging and recognize that this is caused by System.Threading.Thread class which is used for some routine. To simplify the debugging I’ve created a sample .NET application:

    ...

    private void button1_Click(object sender, EventArgs e)
    {
        Thread t = new Thread(DoWork);
        t.Start();
    }

    public void DoWork(object parameter)
    {
        // Do something...
    }

    ...

Each time I’m clicking the button, a thread is created using System.Threading.Thread class. The problem is that looks like the thread do not frees Handles because each click cause number of Handles growing by ~5.

The question is: how can I manually free all Handles created by System.Threading.Thread class?

Thanks in advance.

Answer 1

It's not actually leaking the handles, it's just that the GC hasn't collected them yet. Try changing the code in the button handler so that it loops and creates 500 threads or something and try pressing it a few times and you'll probably see handles being collected.

Answer 2

You don't need to manually free your thread handles, simply dropping all references to your Thread instance should suffice. Given that the thread is no longer running and all references to it are removed, the gargabe collector will free the handles on the next collection.

In your case, it doesn't look like the thread will ever finish.

Answer 3

Its a bug in the CLR

https://connect.microsoft.com/VisualStudio/feedback/details/430646/thread-handle-leak#tabs