reader-writer-problem

I don't expect much code, actually not any code at all, but my mind is currently blank.
What's a better solution than the trivial one (writers wait for all readers to finish)?
I don't really like to use a timer, so do you think it would be a good idea to let the writers do their job every x readers?
The program will be written in C, using pthreads.

Also I know /prog/ won't do my assignment, I just need an idea, or verification if mine would do.

higher default priority to writers + implement aging for all

use file locking

doers_thread {
    when (must_do) {
        wait_for_do (file);
        flock (file);
        for (doers)
            do();
        funlock (file);
    }
}
add_do_thread (readers_thread, reading);
add_do_thread (writers_thread, writing);