Sometimes you would like to dynamically create a mutex. If you don't want to require prior calling to g_thread_init(), because your code should also be usable in non-threaded programs, you are not able to use g_mutex_new() and thus GMutex, as that requires a prior call to g_thread_init(). In theses cases you can also use a GStaticMutex. It must be initialized with g_static_mutex_init() before using it and freed with with g_static_mutex_free() when not needed anymore to free up any allocated resources. Even though GStaticMutex is not opaque, it should only be used with the following functions, as it is defined differently on different platforms. All of the g_static_mutex_* functions apart from g_static_mutex_get_mutex can also be used even if g_thread_init() has not yet been called. Then they do nothing, apart from g_static_mutex_trylock, which does nothing but returning TRUE. Note All of the g_static_mutex_* functions are actually macros. Apart from taking their addresses, you can however use them as if they were functions.
A GStaticMutex works like a GMutex, but it has one significant advantage. It doesn't need to be created at run-time like a GMutex, but can be defined at compile-time. Here is a shorter, easier and safer version of our give_me_next_number()