compare_exchange_weak (C++)

concurrency cpp

Definition

compare_exchange_weak

bool compare_exchange_weak( T& expected, T desired,
                            std::memory_order success,
                            std::memory_order failure ) noexcept;

compare_exchange_weak atomically compares an atomic object with an expected value and, if they are equal, replaces the atomic value with a desired value.

If the comparison fails, the current atomic value is copied into expected.

Formally, for atomic object $x$, expected value $e$, and desired value $d$:

$$\begin{array}{rl}x=e& ⟹x\leftarrow d\text{ and return }\text{true}\\ x\ne e& ⟹e\leftarrow x\text{ and return }\text{false}\end{array}$$