Serious keepalive issue

[freinholz]

I've migrated my project from Yamux to Smux a couple of weeks ago. Most reasionly due to the memory alloc behavior of Yamux After facing some issue, I thought everything is smooth and stable. But the included keepalive functions seems to be far from that.

A debugging revealed that the notifyBucket/check dataReady approch is not reliable under heavy load and with higher RTT. The async notification works, but dataReady is sometimes not correctly set for the timeout checks. It is also very important to mention that this only happens when testing under real life conditions. My local test-cases are all fine, but testing between remote devices reveals the mentioned issue.

One mitigation would be removing the s.Close() right after the dataReady checks. Another would be replacing the check by a more reliable approach. There would also be the option to disable keepalives and implement a real Ping() function.

I've chosen the last option.

Could you please check if a patch integration makes sense or alternatively provide a fix for the keepalive.

Thanks!

Here is my ping patch: ping_patch.txt

[xtaci]

394 if !atomic.CompareAndSwapInt32(&s.dataReady, 1, 0) {

so if this line fails, there is no incoming data, OR(for extreme case), the goroutine for recvLoop() hasn't been scheduled to ?

[xtaci]

for one special case:

the caller of smux don't read the incoming data, then , it blocks on : 309 for atomic.LoadInt32(&s.bucket) <= 0 && !s.IsClosed() {

[xtaci]

https://github.com/xtaci/smux/commit/80072d9b5c44fe531e0e5d7d36b029b87f20065c

[freinholz]

Your patch loooks like a good option for approach 2!

Any comments on the Ping()?

[xtaci]

Pong is not required, IMHO, 'cause we don't need RTT.

[freinholz]

You may don't need it, but I'm using it and there have been plenty of other requests. In addition, it's nice to have a connection control apart from the non-reliable IsClosed() to managed adjacent processes. But okay. So I'll have to managed my own branch.