grpc的keepalive机制升级

[towerWei]

Please see the FAQ in our main README.md before submitting your issue.

Use case(s) - what problem will this feature solve?

在使用grpc的过程当中发现，客户端keepalive机制配置后不生效，并没有按照我设置的间隔去进行ping，查看源码后发现在keepalive的底层，ping之前会检查上次正常发送消息的时间，如果小于设置的间隔就不会进行ping，我们这边想通过ping淘汰一些高延迟的链接（因为目前只有ping超时后高延迟的链接才会关闭并且重新建立）

Proposed Solution

能否加个开关，业务根据自己的需要来判断是否需要跟正常发送的消息时间做比对

Alternatives Considered

Additional Context

[dfawley]

Hi @towerWei,

gRPC sets TCP_USER_TIMEOUT based on the keepalive timeout setting on all clients and servers (1, 2). This means all writes to the network effectively act like the keepalive ping. So, I think this kind of an option should not be required.

(1): client:

grpc-go/internal/transport/http2_client.go

Lines 269 to 274 in d48317f

	if kp.Time != infinity {
	if err = isyscall.SetTCPUserTimeout(conn, kp.Timeout); err != nil {
	return nil, connectionErrorf(false, err, "transport: failed to set TCP_USER_TIMEOUT: %v", err)
	}
	keepaliveEnabled = true
	}

(2): server:

grpc-go/internal/transport/http2_server.go

Lines 232 to 236 in d48317f

	if kp.Time != infinity {
	if err = syscall.SetTCPUserTimeout(rawConn, kp.Timeout); err != nil {
	return nil, connectionErrorf(false, err, "transport: failed to set TCP_USER_TIMEOUT: %v", err)
	}
	}

Please let us know if you have any other questions about this. Thanks!

[towerWei]

这样确实可以实现，但是就把是服务处理的慢还是因为网络延迟混淆了，有些情况下某些服务确实比较慢这个业务侧可以接受，我这边只想检测网络延迟的情况，我理解因为keepalive不涉及业务是最能体现出来的 @dfawley

[dfawley]

@towerWei

TCP_USER_TIMEOUT is based on the TCP ACK and would not be affected by the server's speed. So I believe this should be suitable for your needs.

[towerWei]

抱歉这两天有点其他业务忙，刚抽出时间，但是在tcp通信的底层这个选项应该是用到了所有的消息传递上吧，而不是简单的ping，那岂不是还是影响了正常的处理时长较长的业务 @dfawley

[dfawley]

If anything, the TCP_USER_TIMEOUT should have even less dependence on the application than a ping. A ping requires our library to run and process the ping and manually send an ack back. The kernel would be responsible for handling TCP_USER_TIMEOUT. I believe this should be enough for your needs.

Are you seeing any real problems at this time?