Regression v8.13.0: No connections available for Windows WebKit

[fujii]

I did this

I'm using libcurl for Windows WebKit.
After upgrading libcurl from v8.12.1 to v8.13.0, it has some network errors by browsing some web pages.
For example, by reloading https://www.yomiuri.co.jp/ 2 or 3 times.

I took a libcurl log. it has a lot of No connections available..

I bisected. df67269 is the regression point.

I expected the following

No response

curl/libcurl version

libcurl 8.13.0

operating system

Windows 11

[icing]

Can you describe "has some network errors" more precisely? I suspect that the "No connections available" results from curl counting connections in shutdown against the CURLMOPT_MAX_TOTAL_CONNECTIONS limit.

Before, this was not done and only the "live" connections counted. Same for CURLMOPT_MAX_HOST_CONNECTIONS.

I suspect this results in timeouts in the application?

You could test this by increasing the limits that WebKit seems to set.

/cc @bagder

If this is indeed the issue, we need to decide who libcurl is supposed to handle this. Do we want to immediately close the oldest connection in shutdown when this pressure situation happens. Or do we prioritise a clean shutdown and the application has to adapt?

I think we only get deterministic behaviour for the application, if we force close shutdowns in such situations.

A PR with force closing connections in shutdown under pressure is in #17022

[fujii]

I confirmed it resolved the problem. Thank you very much.

Windows WebKit uses 17 and 6 for CURLMOPT_MAX_TOTAL_CONNECTIONS and CURLMOPT_MAX_HOST_CONNECTIONS.
Yes, timeout was happening. It happened just by reloading https://www.yomiuri.co.jp/ 2 or 3 times. After that, all resource requests timed out from www.yomiuri.co.jp. But, it could load pages from other sites.