Function thread_usleep

thread/thread.cpp:1366–1376

returns 0 if slept well (at lease `useconds`), -1 otherwise

    }
    // returns 0 if slept well (at lease `useconds`), -1 otherwise
    static int thread_usleep(Timeout timeout, thread_list* waitq)
    {
        if (unlikely(timeout.expired())) {
            return yield_as_sleep();
        }

        auto r = prepare_usleep(timeout, waitq);
        switch_context(r.from, r.to);
        assert(r.from->waitq == nullptr);
        return r.from->set_error_number();
    }

    typedef void (*defer_func)(void*);
    static int thread_usleep_defer(Timeout timeout,