When to use 'volatile' or 'Thread.MemoryBarrier()' in threadsafe locking code? (C#)

Question

When should I use volatile/Thread.MemoryBarrier() for thread safety?

Answer 1

What's wrong with

private static readonly object syncObj = new object();
private static int counter;

public static int NextValue()
{
    lock (syncObj)
    {
        return counter++;
    }
}

?

This does all necessary locking, memory barriers, etc. for you. It's well understood and more readable than any custom synchronization code based on volatile and Thread.MemoryBarrier().

---

EDIT

I can't think of a scenario in which I'd use volatile or Thread.MemoryBarrier(). For example

private static volatile int counter;

public static int NextValue()
{
    return counter++;
}

is not equivalent to the code above and is not thread-safe (volatile doesn't make ++ magically become thread-safe).

In a case like this:

private static volatile bool done;

void Thread1()
{
    while (!done)
    {
        // do work
    }
}

void Thread2()
{
    // do work
    done = true;
}

(which should work) I'd use a ManualResetEvent to signal when Thread2 is done.