$len = @fwrite($this->_socket, $send_buffer);
// send successful.
if ($len === strlen($send_buffer)) {
    return true;
}
// Send only part of the data.
if ($len > 0) {
    $this->_sendBuffer = substr($send_buffer, $len);
} else {
    // Connection closed?
    if (!is_resource($this->_socket) || feof($this->_socket)) {
        self::$statistics++;
        if ($this->onError) {
            try {
                call_user_func($this->onError, $this, WORKERMAN_SEND_FAIL, 'client closed');
            } catch (\Exception $e) {
                Worker::log($e);
                exit(250);
            } catch (\Error $e) {
                Worker::log($e);
                exit(250);
            }
        }
        $this->destroy();
        return false;
    }
    $this->_sendBuffer = $send_buffer;
}
Worker::$globalEvent->add($this->_socket, EventInterface::EV_WRITE, array($this, 'baseWrite'));

這段代碼中 當(dāng)$len != strlen($send_buffer)的時(shí)候，為什么不繼續(xù) fwrite將剩余的數(shù)據(jù)發(fā)送出去，而要去監(jiān)聽(tīng)
baseWrite函數(shù)， 在baseWrite里將剩余數(shù)據(jù)發(fā)送出去