Tim was debugging one of those multithreading bugs, where there appeared to be a race condition of some kind. The developer who had initially written the code denied that such a thing could exist: Its impossible, I used locks to synchronize the threads!

Well, he did use locks at the very least.

/// 

/// Performs the synchronisation
/// 
/// Current state
private void Synchronize(object state)
{
    // Take care that this can only run in one thread at a time
    var lockThis = new Object();
    lock (lockThis)
    {
        //…code…
    }
}

There is of course, one problem. The object you use for the lock needs to be shared across threads. This is less a lock in the sense of an air lock and more a lock in the sense of a complete hull breach.

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https://thedailywtf.com/articles/synchronized-threads