reordering atomic operations in C++

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);.