std::call_once, when should it be used?

Question

The std::call_once function, introduced in C++11, ensures a callable is called exactly one time, in a thread safe manner.

Since this can be achieved by other means - when should std::call_once be used? What type of problems is it intended to address?

Please provide examples.

Answer 1

Example: I use it for libcURL to retrieve http(s) data from websites. In libcURL, you have to do a one-time global initialization before you're able to use the library. Given that initialization is not thread-safe, but requesting data from websites is thread-safe, I use call_once that calls my initialization only once, no matter in what thread and whether it's called concurrently.