| .. title:: clang-tidy - darwin-dispatch-once-nonstatic |
| |
| 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 <https://developer.apple.com/documentation/dispatch/1447169-dispatch_once>`_ |
| for more information. |
