How thread safe are static fields?

[JoeRip]

In the following struct:

   public struct myStruct
        {
            public static int CumulativeCountOfInstances;

            public myStruct(int SomeUnusedData)
            {
                CumulativeCountOfInstances++;
            }
        }

If concurrent processes are creating myStruct structs, what prevents collisions as each instance tries to increment CumulativeCountOfInstances?

[Mark Salsbery]

Nothing prevents it. Maybe a good place for an interlocked increment :) How are different processes sharing the same variable? Or did you mean concurrent threads? Mark

Mark Salsbery Microsoft MVP - Visual C++ :java:

[JoeRip]

I definitely mean concurrent threads. Friday afternoons are very hard on my concentration. So I should use Interlocked increments from my constructor, AND I should should use Interlocked exchange any time I want to read this value? Dang, static isn't as static as I thought it was :-)

[Mark Salsbery]

If you use Interlocked.Increment() / Interlocked.Decrement() then the new value will be returned (an increment and a read are combined in one atomic operation). Reading (for integer types) is atomic (except for 64-bit integers on a 32-bit processor) so there's no Interlocked.Read except for longs. You could use Interlocked.Exchange() if that's what you need to do, but it's not appropriate for just reading the value (what value would you exchange?). To write/modify the variable beyond the atomic operations provided by the Interlocked class, you'll need to use some other type critical section, like lock. Mark

Mark Salsbery Microsoft MVP - Visual C++ :java:

[JoeRip]

Thanks again. I wondered why there was no Read for Int32.