Memory Model
The foundation of multithreading is a well-defined memory model. This memory model has to deal with the following points:
- Atomic operations: Operations that can be performed without interruption.
- Partial ordering of operations: Sequence of operations that must not be reordered.
- Visible effects of operations: Guarantees when operations on shared variables are visible in other threads.
The C++ memory model has a lot in common with its predecessor: the Java memory model. On the contrary, C++ permits the breaking of sequential consistency. The sequential consistency is the default behaviour of atomic operations.
The sequential consistency provides two guarantees.
- The instructions of a program are executed in source code order.
- There is a global order of all operations on all threads.
