Double ping pong that crashes the app.

[notcome]

Describe the bug

So this is a follow up to my previous issue #435 . I mentioned that I often ran into crash on the following line:

postgres-nio/Sources/ConnectionPoolModule/PoolStateMachine+ConnectionGroup.swift

Line 441 in c826992

self.stats.availableStreams -= closeAction.maxStreams

So I have decided to to modify the source code a bit, added some log, and observed the following thing:

1. availableStreams will reduce 1 before ping pong, and increase back afterwards;
2. when the issue happens, availableStreams is already at 0;
3. the issue only happens if, according to the log, two ping pong happens in vert short interval.

So I suppose this is just a strange weird data race around keep alive timers. But I have seen no pattern why this might happen, nor can I reliably reproduce this issue. Plus I suppose we will never see it if the ping pong can finish in very short period.

I wonder if there is anything I can do to help you people track this down. I am a bit occupied right now, but I will try to add some log and data race check on a local fork when I get some free time.

Expected behavior
No error.

Environment
Vapor Framework version: 4.84.6
Vapor Toolbox version: 18.7.4
OS version: macOS 14.0 (23A344)

[fabianfett]

@notcome Thanks I'll look into this. As a workaround you can disable keep-alives for now:

clientConfiguration.options.keepAliveBehavior = nil

[fabianfett]

Released in 1.19.1. Please check if the issue is fixed for you now.