Comments (1)
感谢关注和支持!
- ...如果同一个epoll 里多个conn 读事件到来,那么处理的时候,后面的就只能等前面的结束了。
默认使用的 LT,LT模式下,如果本次 epoll loop 1 中派送事件给异步协程池去读,读协程池尚未读取时就可能 epoll loop 1 结束,因为尚未读取,则仍然可读、LT模式会再次触发 epoll_wait 返回,所以进入 epoll loop 2、重复去派发读事件,造成事件和实际syscall重复浪费。
不同模式压测后我的环境下 LT 性能最好,而且即使异步读,涉及协议解析之类的 cpu 消耗,实际并发度仍然受到核心数限制,单独的异步读协程池数量也不适合太大、也还是涉及排队的问题,所以默认使用的 LT。
但是 nbio 是支持 epoll mod 可配置的,也支持 ET,但是不支持 ET+ONESHOT,因为 ONESHOT 每次都要重新添加事件、性能比较差一些。
EpollMod
参数配置成 EPOLLET,用户还可以使用 g.OnRead
自行定制读取方式是同步还是异步或者其他的细节,当设置了 g.OnRead
时,g.OnData
失效。
IO协程数量也是可配置的,所以,只要用户喜欢,像runtime那样只使用一个 epoll loop + ET + 多个读协程都是可以的。
从使用的自由度来讲,用户可以定制不同的读策略从而自由选择 Reactor 或 Proactor 。
2.write 会限制包大小,直接返回错误,而不是底层分批处理掉,是出于大包攻击考虑吗?
nbio.Conn 是根据配置做 write size 限制,默认的 MaxWriteBufferSize
为0则不限制。nbio.Conn提供的是基础设施,就像 syscall write 一样,实际的写入逻辑应由用户控制。
MaxWriteBufferSize
主要是避免应用层不慎、窗口拥塞缓存的待写入数据太大等情况可能导致的OOM。除了 MaxWriteBufferSize
,用户还应该合理使用 SetWriteDeadline
等、对僵尸连接、窗口拥塞已经不健康的连接进行及时关闭
3.调用底层中读写的代码都有一个 if n<0 的判断,真的会出现小于0吗?
syscall read/write 的返回值可以查看下 man 2 read/write,返回值-1时配合对应的 errno 进行处理:
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