Function pthread_sigmask 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pthread_sigmask(
    how: c_int,
    set: *const sigset_t,
    oldset: *mut sigset_t,
) -> c_int

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

Examines or changes (or both) the calling thread’s signal mask.

Upon success, returns 0. Upon failure, returns an error number.