Handling edge cases on connSet(Read/Write)Handler about valkey

[madolson]

I suppose another option would be to allow specifying an error handler in the API, which get's called if the API fails. That would allow us to better support the error case.

@PingXie Just want to get your opinion on this. I think we should do three things:

1. Change connSetHandler so it returns a void.
2. Attempt to handle the case where an fd is out of bounds by doing an in-place realloc of the array and log a message.
3. Call the error handler when we encounter an error.

[PingXie]

Both 1) and 2) make sense to me. Can you elaborator on 3)? I am not sure which error handler this is. If we can realloc, there isn't much for the caller to handle anyway; but if we can't, I think we have a bigger issue.

[madolson]

but if we can't, I think we have a bigger issue.

I guess I just don't know if we actually have bigger issues. Today we might just be silently ignoring issues on error paths which get resolved later. I can imagine there are cases where a client was accepted, has already been closed by the file system by some later time we install the handler, and we gracefully ignore the epoll_ctl command since the client will get eventually closed anyways.

So, my thought for the error handler, is just to make sure we aren't "leaking" the client resource (for the normal client case) and the clusterbus (in the cluster case). If after some time in product we don't observe any issue, we could remove it.

[PingXie]

If we do 1) and 2), we will be able to handle all errors internally to aeApiAddEvent so we probably don't need an error handler callback. Should we consider a fix in Valkey 8.0?