Is Volatile.Read / Volatile.Write for "double" atomic?

Question

MSDN states that:

Reads and writes of other types, including long, ulong, double, and decimal, as well as user-defined types, need not be atomic.

C# 7.0 draft specification - Variables - 9.6 Atomicity of variable references

Will Volatile.Write(Double, Double) work as atomic operation? If so how this is guaranteed?

Is it safe to do Volatile.Write(ref mydouble, value); in one thread and Volatile.Read(ref mydouble) in another where mydouble has double type?

That was general question. Another question - what should I do in this particular situation:

• 2 processors Xeon x64 server
• Windows + MS .NET 4.5
• read/write double from different threads
• SMALLEST latency (need smallest because i'm writing HFT software)

Answer 1

No, Volatile is not atomic, and it is not safe in an SMP (>1 processor) system to assume so. It is safe on a uniprocessor machine.

Unless you really need the performance, you probably want Interlocked instead, either Interlocked.Exchange or Interlocked.Read.