reordering atomic operations in C++
c++, memory-model, multithreading, stdatomic
Solution
By default operations on atomic variables are done using the `memory_order_seq_cst` semantics, which guarantees that no reordering will be done.
Thus the line: `value = 1` cannot be reordered below the atomic assignment: `value = 1`, so the line `std::cout << value;` will always print 1.
By the same rules, the line: `std::cout << value;` cannot be reordered above the line: `while (!ready);`.
Problem
Suppose I have 2 threads: ``` int value = 0; std::atomic<bool> ready = false; thread 1: value = 1 ready = true; thread 2: while (!ready); std::cout << value; ``` Is this program able to output 0? I read about the C++ memory model - specifically, sequential consistency, which I believe is the default, and it wasn't particularly clear. Is the compiler only required to put atomic operations in the correct order relative to each other, or is it required to put atomic operations in the right order relative to all other operations?