void silc_cond_wait(SilcCond cond, SilcMutex mutex);

    Waits for condition variable `cond' to be signalled.  This function
    will block the calling thread until the condition variable is
    signalled.  The `mutex' must be locked before calling this function.
    The `mutex' will be unlocked inside this function.  After this
    function returns the `mutex' is in locked state again.

    silc_mutex_lock(lock);
    while (c->a == NULL)
      silc_cond_wait(cond, lock);
    ...
    silc_mutex_unlock(lock);