Boost::thread fails to pull -pthread in cmake parent project config

[emaxerrno]

given a cmake project definition of

ExternalProject_Add(seastar
  URL https://github.com/vectorizedio/seastar/archive/cd38452d.tar.gz
  URL_MD5 282f28305918ec65017c21719de5b887
  INSTALL_DIR    @V_DEPS_INSTALL_DIR@
  CMAKE_COMMAND ${CMAKE_COMMAND} -E env ${cmake_build_env} ${CMAKE_COMMAND}
  CMAKE_ARGS
    ${common_cmake_args}
    -DBoost_USE_STATIC_LIBS=OFF
    -DBoost_NO_BOOST_CMAKE=ON
    -DBoost_NO_SYSTEM_PATHS=TRUE
    -DProtobuf_USE_STATIC_LIBS=ON
    -DSeastar_INSTALL=ON
    -DSeastar_DPDK=@RP_ENABLE_DPDK@
    -DSeastar_APPS=ON
    -DSeastar_DEMOS=OFF
    -DSeastar_DOCS=OFF
    -DSeastar_TESTING=OFF
    -DSeastar_CXX_FLAGS=-Wno-error
    -DSeastar_LD_FLAGS=-pthread      # ................ bug/workaround
    -DSeastar_STD_OPTIONAL_VARIANT_STRINGVIEW=ON
    -DSeastar_CXX_DIALECT=c++17
  DEPENDS
    ${default_depends}
    fmt
    boost
    protobuf
    dpdk
    yaml-cpp
    c-ares
    gnutls
    lz4
    hwloc
    numactl
    xml2
    xz
    cryptopp
    lksctp-tools
    zlib)

I noticed that the main definition of seastar in cmakelist.txt under some configurations fails to import pthread for boost:

target_link_libraries (seastar
  PUBLIC
    Boost::boost
    Boost::program_options
    Boost::thread
    # .................. I can add `pthread` here and everything works
    c-ares::c-ares
    cryptopp::cryptopp
    fmt::fmt
    lz4::lz4
  PRIVATE
    ${CMAKE_DL_LIBS}
    Boost::filesystem
    GnuTLS::gnutls
    StdAtomic::atomic
    StdFilesystem::filesystem
    lksctp-tools::lksctp-tools
    protobuf::libprotobuf
    rt::rt
    yaml-cpp::yaml-cpp)

I am not sure if the issue is coming from our own boost cmake module - from the comments

# The following :prop_tgt:`IMPORTED` targets are also defined::
#
#   Boost::boost                  - Target for header-only dependencies
#                                   (Boost include directory)
#   Boost::<C>                    - Target for specific component dependency
#                                   (shared or static library); <C> is lower-
#                                   case
#   Boost::diagnostic_definitions - interface target to enable diagnostic
#                                   information about Boost's automatic linking
#                                   during compilation (adds BOOST_LIB_DIAGNOSTIC)
#   Boost::disable_autolinking    - interface target to disable automatic
#                                   linking with MSVC (adds BOOST_ALL_NO_LIB)
#   Boost::dynamic_linking        - interface target to enable dynamic linking
#                                   linking with MSVC (adds BOOST_ALL_DYN_LINK)
#
# Implicit dependencies such as Boost::filesystem requiring
# Boost::system will be automatically detected and satisfied, even
# if system is not specified when using find_package and if
# Boost::system is not added to target_link_libraries.  If using
# Boost::thread, then Threads::Threads will also be added automatically.
#

But it actually is not pulling in Threads::Threads which in normal speak means -lpthread

I can fix the problem for all platforms by adding the pthread as I mentioned in the context above, but not sure if there is a more elegant solution.

Maybe someone w/ a bit more cmake-foo experience can help.

The problem is manifested like so:

on a link.txt produced by cmake on a -GMake

/bin/c++     CMakeFiles/main.dir/main.cc.o  -o main seastar/libseastar.a /usr/lib64/libboost_program_options.so /usr/lib64/libboost_thread.so /usr/lib64/libboost_chrono.so /usr/lib64/libboost_date_time.so /usr/lib64/libboost_atomic.so -lpthread /usr/lib64/libcares.so /usr/lib64/libcryptopp.so /usr/lib64/libfmt.so.5.2.1 -Wl,--as-needed /usr/lib64
/liblz4.so -ldl /usr/lib64/libboost_filesystem.so /usr/lib64/libgnutls.so -latomic /usr/lib64/libsctp.so /usr/lib64/libprotobuf.so -lrt /usr/lib64/libyaml-cpp.so /usr/lib64/libhwloc.so /usr/lib64/libnuma.so 

Notice the -lpthread after boost_atomic

The issue is that on an application that is just pulling cmake as an ExternalProject_add the -lpthread isn't added to the link.txt files (using the -GMake generator for cmake).

I'm not sure if there is a preference.

In summary

There is a problem with externalproject_add importing seastar.

There are 2 fixes.

1. We push the user to always add -DSeastar_LD_FLAGS=-pthread
2. We add -pthread after boost::thread in the main cmakelist.txt file

[emaxerrno]

Ok, further digging shows I was right, we'll just need to fix our boost for newer versions

CMake Warning at build/debug/v_deps_install/lib64/cmake/Seastar/FindBoost.cmake:839 (message):
  New Boost version may have incorrect or missing dependencies and imported
  targets

We use boost 1.70.0 from source

We can either close this ticket, or I can submit a patch with the -pthread fix i mentioned above

/cc @denesb

[espindola]

Alexander Gallego <[email protected]> writes:

Ok, further digging shows I was right, we'll just need to fix our boost for newer versions ``` CMake Warning at build/debug/v_deps_install/lib64/cmake/Seastar/FindBoost.cmake:839 (message): New Boost version may have incorrect or missing dependencies and imported targets

./cmake/bundled_boost/FindBoost.cmake is simply a copy from cmake. We did that to support older versions of cmake I think. Maybe we can just delete our copy now and require that users have a cmake version that supports the boost version they are using? Cheers, Rafael

[emaxerrno]

Works for me.