Writing/reading basic data type simultaneously

Question

In C++, say I have a variable of basic data type, like int counter , that is used by many threads. In order to modify counter , a thread must obtain a simple lock first. But I want the value to be readable at any time, whether it is locked or not.

When a thread reads counter while some other thread is modifying it, do I have any guarantee to at least get either the pre-write or post-write value, rather than some corrupted value?

For example:

//counter == 10
counter += 5;
//counter == 15

Will all threads reading counter around this time be guaranteed to at least read 10 or 15 ? Instead of some strange value like -834289 .

If the answer is implementation specific, I'm using Visual Studio 2015.

Answer 1

No it's not. Use a std::atomic_int

Answer 2

在Intel架构上 ，字大小值的分配通常是原子的，因此您不会读取损坏的值。

Answer 3

Look at the interlocked family of functions here:

https://msdn.microsoft.com/en-us/library/windows/desktop/ms686360(v=vs.85).aspx

The one you are looking for is most likely:

InterlockedAdd