C11 thread check is not working with glibc 2.28

[Oxymoron79]

Description

Glibc version 2.28 added support for C11 threads (see the release notes: https://www.sourceware.org/ml/libc-alpha/2018-08/msg00003.html).

But the check for C11 threads in configure.librdkafka (https://github.com/edenhill/librdkafka/blob/master/configure.librdkafka#L46) does not seem to
detect the C11 threads support on systems using glibc >= 2.28, because the link option
-lpthread is not used for the check.

I suspect that this leads to similar problems as #1998.

How to reproduce

On a system with glibc >= 2.28 (e.g. Arch Linux):

./configure
cat config.h | grep WITH_C11THREADS

WITH_C11THREADS is not defined in config.h, which leads to tinycthread being compiled without C11 thread support.

Checklist

Please provide the following information:

• librdkafka version (release number or git tag): v0.11.1
• Operating system: Arch Linux (x86_64)
• Critical issue

[edenhill]

Interesting, do you know of a docker image with glibc 2.28?

[Oxymoron79]

Ubuntu 18.10 (Cosmic) seems to be shipping glibc 2.28: https://packages.ubuntu.com/cosmic/libc6
The cosmic tag of the ubuntu docker image should therefore include it: https://hub.docker.com/_/ubuntu

[Oxymoron79]

@edenhill Were you able to reproduce the issue?

[grafitto]

I am also having the same error on Manjaro

[edenhill]

This will be fixed in the upcoming v1.0.0 release.