darwin-dispatch-once-nonstatic¶
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 of Apple’s dispatch_once documentation for more information.