Avoid pthread ”_np” functions for portability?

[ghost]

Compiling on Alpine Linux currently fails due to the non-existence of non-standard extensions of GNU to pthread functions. E.g., pthread_rwlockattr_setkind_np is not in the musl C library. I recommmend to work around code like this, in XrdSysPthread, to welcome Alpine Linux users to the world of XRootD. Is it possible?

[simonmichal]

@peter-jansson : thanks for bringing this up!

First of all, unfortunately I couldn't find any predefined macro that will tell us if we are using the musl C library (I am open to any suggestions). But let's say we do in cmake something like:

check_function_exists( pthread_rwlockattr_setkind_np, HAS_NP)
if( NOT HAS_NP )
  add_compile_definitions( __MUSL__ )
endif()

Then we can use the __MUSL__ macro to make sure the _np functions are not used.

However, having this in place (and fixing few other small issues) I run into the following problems:

• error: 'innetgr' was not declared in this scope
• the uuid/uuid.h header is missing (AFAIU the there's not package providing it)
• error: 'timeval' does not name a type

Now, I'm not sure we can work around those problems, especially the missing uuid/uuid.h header (I couldn't find any package providing it).

If you are willing to contribute, please open a PR and we can try to address those issues one by one.

[abh3]

Where are we on this ticket?

[ghost]

• the uuid/uuid.h header is missing (AFAIU the there's not package providing it)

The util-linux-dev package on Alpine Linux contains uuid/uuid.h from libuuid in util-linux at kernel.org.

[amadio]

Support for musl is (maybe partially) addressed in #1632, but I don't see any changes related to pthread functions there. We do intend to add support for it, although we cannot give a particular timeline, as we have to prioritize current supported platforms. I hope to test/merge musl support as part of the next feature release, 5.6.

[amadio]

Fixed with merge of musl branch into master (#1908). I also added a build on alpine to GitHub Actions.