pub unsafe extern "C" fn fftwf_threads_set_callback(
parallel_loop: Option<unsafe extern "C" fn(work: Option<unsafe extern "C" fn(arg1: *mut c_char) -> *mut c_void>, jobdata: *mut c_char, elsize: usize, njobs: c_int, data: *mut c_void)>,
data: *mut c_void,
)