export pthread dependency

[dirk-thomas]

With only FastRTPS several examples fail to link since it seems to use pthread but doesn't export it (at least on Xenial, maybe also with other RMW impl. but currently I only have FastRTPS).

• http://ci.ros2.org/job/ci_linux/1159/
• http://ci.ros2.org/job/ci_osx/937/
• http://ci.ros2.org/job/ci_windows/1215/

[wjwwood]

I doubt this will work on Windows and maybe not even on OS X or Linux with clang.

[wjwwood]

Maybe CMake or our code (ignore if missing) is filtering it out? I don't think pthread is a valid library target on Windows.

[dirk-thomas]

I wrapped it in a conditional for NOT WIN32 (despite CI passing).

Since we use pthread in various other places on all non-Windows platforms I will keep that part as-is:

• https://github.com/ros2/rmw_connext/blob/6f1113f38be1cbb388311a2bcd0bc658edf29c8e/connext_cmake_module/cmake/Modules/FindConnext.cmake#L303
• https://github.com/ros2/rmw_opensplice/blob/d63fed94064e111b7dff6904f4475faf9f56c9bb/opensplice_cmake_module/cmake/Modules/FindOpenSplice.cmake#L85

[wjwwood]

Sounds good to me +1

[jacquelinekay]

interesting, I wonder what happens with a Windows FastRTPS-only build.

[jacquelinekay]

I confirmed on a Xenial VM that pthread linkage is an issue and that this fixes the build (for rmw_fastrtps_cpp yet, the rest of the workspace is building now). +1