Question

What is the difference (if any) between using

void MethodName()
{
    lock(this)
    {
        // (...)
    }
}

or

private object o = new object();
void MethodName()
{
    lock(o)
    {
        // (...)
    }
}

?

Is there a difference in performance? Style? Behaviour?

Answer 1

The difference is that anyone can lock on your instance, but only you can lock on a private object.

This helps prevent deadlocks.

For example:

Let’s say that Microsoft used lock(this) in the Control class.

Then, if someone else locks on a Control instance, his lock would prevent the code in Control from running, which is not what he wants.

This is particularly bad if you lock on types that are shared across AppDomains