Proposal: Atomic Operations¶

Note

Feature awaiting further design consideration.

Atomic operations provide well-defined behaviour when multiple threads interact.

Usage¶

void f(atomic int& value) {
        value++;
}

This code will generate code that atomically increments the int referred to by value.

Implementation¶

Atomic keyword¶

The atomic keyword makes a type atomic by wrapping it with atomic_t:

atomic int -> atomic_t<int>

atomic has no effect other than this and does not introduce a new type tag (i.e. unlike const, lval and ref).

Atomic type¶

atomic_t is a type that supports methods such as increment, decrement, addassign, etc. and calls to the wrapped type’s atomic_increment, atomic_decrement, atomic_addassign, etc.

The code above is therefore approximately equivalent to:

void f(int& value) {
        value.atomic_increment();
}

Loading values¶

Values can be loaded atomically simply by an implicit cast, which calls the atomic_load method of the wrapped type:

int f(atomic int& value) {
        return value;
}

Storing values¶

void f(atomic int* value) {
        *value = 42;
}