Function pthread_atfork 

#[unsafe(no_mangle)]
pub extern "C" fn pthread_atfork(
    prepare: Option<extern "C" fn()>,
    parent: Option<extern "C" fn()>,
    child: Option<extern "C" fn()>,
) -> c_int

See https://pubs.opengroup.org/onlinepubs/9799919799/functions/pthread_atfork.html.