[Pkg-cmake-team] Bug#915148: Bug#915148: cmake: regression in ros-ros-comm build

[Brad King]

On 12/6/18 4:16 PM, Jochen Sprickerhof wrote:
> after reading up on this, I think this needs fixing in cmake.
> 
> So neither adding -lpthread,
> nor adding /usr/lib/x86_64-linux-gnu/libpthread.so
> seems correct to me.

Both are valid ways to link to the pthread library, which is all
the `-pthread` flag does when used to drive linking.

> I will revert the workaround in ros-catkin if you agree.

The patch here:

  http://launchpadlibrarian.net/399812910/ros-catkin_0.7.14-7_0.7.14-7ubuntu1.diff.gz

is not a workaround.  The input to that logic could contain -lfoo
generated by other means for other libraries.  This case just
happened to expose the existing bug in that logic.

Actually looking at the applied fix

  https://sources.debian.org/src/ros-catkin/0.7.14-8/cmake/templates/pkgConfig.cmake.in/#L118

that logic may need additional work to handle plain `-pthread`
or other link flags.

> [FindThreads] promotes CMAKE_THREAD_PREFER_PTHREAD to get -pthread

It's THREADS_PREFER_PTHREAD_FLAG for that.

CMake's FindBoost and FindThreads could use some work to use
`-pthread` more completely (perhaps with a policy to use it
by default on appropriate compilers), and there is an issue
related to this here:

  https://gitlab.kitware.com/cmake/cmake/issues/18638

However, that does not mean the above change should be reverted.

-Brad