Basics of the Memory Model

From the concurrency point of view, there are two main aspects of the memory model:

• What is a memory location?
• What happens if two threads access the same memory location?

Let me answer both questions.

What is a memory location?

A memory location is according to cppreference.com

• an object of scalar type (arithmetic type, pointer type, enumeration type, or std::nullptr_t),
• or the largest contiguous sequence of bit fields of non-zero length.

Here is an example of a memory location:

struct S {
    char a;        // memory location #1
    int b : 5;     // memory location #2
    int c : 11,    // memory location #2 (continued)
          : 0,
        d : 8;     // memory location #3
    int e;         // memory location #4
    double f;      // memory location #5
    std::string g; // several memory locations
};

First, the object obj consists of seven sub-objects and the two bit fields b, and c share the same memory location.

Here are...