Getting Visual Studio to Display Deadlocked Tasks

It’s not a new feature — since it existed since freaking Visual Studio 2010!

Yesterday during an unrelated meeting, Alon Fliess showed a bunch of us developers how Visual Studio detects deadlocks in tasks (automatically) and shows the current task status in both Parallel Tasks and Tasks debug windows (duh).

I got home late but I wanted to experiment and see what would happen, so I wrote a simple program to see how well Visual Studio understands the bugs I can throw at it:

static void Main(string[] args) 
{ 
    int taskCount = 6; 
    var tasks = new Task[taskCount]; 
    var autoResetEvent = new AutoResetEvent(false); 
    for (int i = 0; i < taskCount; i++) 
    { 
        tasks[i] = Task.Factory.StartNew(state => 
        { 
            var index = (int)state; 
            if (index < 3) 
            { 
                tasks[(index + 1) % 3].Wait(); 
            } 
            else if (index == 3) 
            { 
                Task.Factory.StartNew(() => 
                { 
                    while (true) { } 
                }).Wait(); 
            } 
            else 
            { 
                autoResetEvent.WaitOne(); 
            } 
        }, i); 
    } 

    Task.WaitAll(tasks); 

    autoResetEvent.Set(); 
}

After a few seconds I paused/breaked execution and got the following (Debug –> windows –> Tasks):

So out of the 6 tasks I spawned the first three deadlocks are detected by VS, Three tasks that show as blocked (waiting for AutoResetEvent and waiting for another task to complete). The only task that shows as running is the one that happily burning CPU on awhile loop that would never end (also known as the Halting problem).

That’s good enough for me. 

I guess it’s another case of a useful feature that I always wanted but didn’t know already existed.

Happy coding…