void silc_rwlock_rdlock(SilcRwLock rwlock);

    Acquires read lock of the read/write lock `rwlock'.  If the `rwlock'
    is locked by a writer the current thread will block until the other
    thread has issued silc_rwlock_unlock for the `rwlock'.  This function
    may be called multiple times to acquire the read lock.  There must be
    same number of silc_rwlock_unlock calls.  If `rwlock' is NULL this
    function has no effect.