.net - Interlocked.Xxx 方法是否保证在所有数据缓存中更新值？

Question

例子:

Thread a:  Interlocked.Increment(ref x);

Thread b:  int currentValue = x;

假设线程 b 在线程 a 之后执行，线程 b 中的“currentValue”是否保证是递增的值？或者，线程 b 是否需要执行 Thread.VolatileRead(ref x)？

Answer 1

从技术上讲，这取决于运行 .NET 的 CPU，但对于任何常见的 CPU，答案是肯定的，Interlocked.Increment 可以保证缓存一致性。它acts as a memory barrier按照 MESI 的要求。

a CPU can have in its cache a line which is invalid, but where it doesn't yet know that line is invalid - the invalidation queue contains the invalidation which hasn't yet been acted upon. (The invalidation queue is on the other "side" of the cache; the CPU can't scan it, as it can the store buffer). As a result, memory barriers are required.

http://en.wikipedia.org/wiki/MESI_protocol (x86)

MOESI(用于 AMD64 芯片)非常相似:

http://en.wikipedia.org/wiki/MOESI_protocol (AMD64)