Function sigprocmask 

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

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

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

Upon success, returns 0. Upon failure, returns -1, sets errno to indicate the error, and does not change the signal mask.

Use of this function is unspecified in a multi-threaded process.