Is the “switch” statement evaluation thread-safe?

Question

Consider the following sample code:

class MyClass
{
    public long x;

    public void DoWork()
    {
        switch (x)
        {
            case 0xFF00000000         


        

Answer 1

Yes, the switch statement itself, as shown in your question, is thread-safe. The value of field x is loaded once into a (hidden) local variable and that local is used for the switch block.

What isn't safe is the initial load of the field x into a local variable. 64-bit reads aren't guaranteed to be atomic, so you could be getting stale and/or torn reads at that point. This could easily be resolved by using Interlocked.Read, or similar, to explicitly read the field value into the local in a thread-safe way:

long y = Interlocked.Read(ref x);
switch (y)
{
    // ...
}