.Net CompareExchange reordering

Question

Can the compiler or processor reorder the following instructions so that another Thread sees a == 0 and b == 1?

Assuming int a = 0, b = 0; somewhere.

System.Threading.Interlocked.CompareExchange<int>(ref a, 1, 0);
System.Threading.Interlocked.CompareExchange<int>(ref b, 1, 0);

Answer 1

No. Using Interlock will signal a full memory fence. “That is, any variable writes before the call to an Interlocked method execute before the Interlocked method, and any variable reads after the call executes after the call.” [1] They use volatile read/write methods to prevent the b = 1 before a = 1.

[1]: Jeffrey Richter: “CLR via C# - Third Edition” part V Threading, page 803