tidy - darwin-dispatch-once-nonstatic — Extra Clang Tools 22.0.0git documentation (original) (raw)

Finds declarations of dispatch_once_t variables without static or global storage. The behavior of using dispatch_once_t predicates with automatic or dynamic storage is undefined by libdispatch, and should be avoided.

It is a common pattern to have functions initialize internal static or global data once when the function runs, but programmers have been known to miss the static on the dispatch_once_t predicate, leading to an uninitialized flag value at the mercy of the stack.

Programmers have also been known to make dispatch_once_t variables be members of structs or classes, with the intent to lazily perform some expensive struct or class member initialization only once; however, this violates the libdispatch requirements.

See the discussion section ofApple’s dispatch_once documentationfor more information.