Modules/FindThreads.cmake

# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
# file Copyright.txt or https://cmake.org/licensing for details.

#[=======================================================================[.rst:
FindThreads
-----------

This module determines the thread library of the system.

The following variables are set

::

  CMAKE_THREAD_LIBS_INIT     - the thread library
  CMAKE_USE_WIN32_THREADS_INIT - using WIN32 threads?
  CMAKE_USE_PTHREADS_INIT    - are we using pthreads
  CMAKE_HP_PTHREADS_INIT     - are we using hp pthreads

The following import target is created

::

  Threads::Threads

If the use of the -pthread compiler and linker flag is preferred then the
caller can set

::

  THREADS_PREFER_PTHREAD_FLAG

The compiler flag can only be used with the imported
target. Use of both the imported target as well as this switch is highly
recommended for new code.

This module is not needed for C++11 and later if threading is done using
``std::thread`` from the standard library.
#]=======================================================================]

include (CheckLibraryExists)
include (CheckSymbolExists)
set(Threads_FOUND FALSE)
set(CMAKE_REQUIRED_QUIET_SAVE ${CMAKE_REQUIRED_QUIET})
set(CMAKE_REQUIRED_QUIET ${Threads_FIND_QUIETLY})

if(CMAKE_C_COMPILER_LOADED)
  include (CheckIncludeFile)
elseif(CMAKE_CXX_COMPILER_LOADED)
  include (CheckIncludeFileCXX)
else()
  message(FATAL_ERROR "FindThreads only works if either C or CXX language is enabled")
endif()

# Internal helper macro.
# Do NOT even think about using it outside of this file!
macro(_check_threads_lib LIBNAME FUNCNAME VARNAME)
  if(NOT Threads_FOUND)
     CHECK_LIBRARY_EXISTS(${LIBNAME} ${FUNCNAME} "" ${VARNAME})
     if(${VARNAME})
       set(CMAKE_THREAD_LIBS_INIT "-l${LIBNAME}")
       set(CMAKE_HAVE_THREADS_LIBRARY 1)
       set(Threads_FOUND TRUE)
     endif()
  endif ()
endmacro()

# Internal helper macro.
# Do NOT even think about using it outside of this file!
macro(_check_pthreads_flag)
  if(NOT Threads_FOUND)
    # If we did not found -lpthread, -lpthread, or -lthread, look for -pthread
    if(NOT DEFINED THREADS_HAVE_PTHREAD_ARG)
      message(STATUS "Check if compiler accepts -pthread")
      if(CMAKE_C_COMPILER_LOADED)
        set(_threads_src ${CMAKE_CURRENT_LIST_DIR}/CheckForPthreads.c)
      elseif(CMAKE_CXX_COMPILER_LOADED)
        set(_threads_src ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/FindThreads/CheckForPthreads.cxx)
        configure_file(${CMAKE_CURRENT_LIST_DIR}/CheckForPthreads.c "${_threads_src}" COPYONLY)
      endif()
      try_compile(THREADS_HAVE_PTHREAD_ARG
        ${CMAKE_BINARY_DIR}
        ${_threads_src}
        CMAKE_FLAGS -DLINK_LIBRARIES:STRING=-pthread
        OUTPUT_VARIABLE OUTPUT)
      unset(_threads_src)

      if(THREADS_HAVE_PTHREAD_ARG)
        set(Threads_FOUND TRUE)
        message(STATUS "Check if compiler accepts -pthread - yes")
      else()
        message(STATUS "Check if compiler accepts -pthread - no")
        file(APPEND
          ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log
          "Determining if compiler accepts -pthread failed with the following output:\n${OUTPUT}\n\n")
      endif()

    endif()

    if(THREADS_HAVE_PTHREAD_ARG)
      set(Threads_FOUND TRUE)
      set(CMAKE_THREAD_LIBS_INIT "-pthread")
    endif()
  endif()
endmacro()

# Do we have pthreads?
if(CMAKE_C_COMPILER_LOADED)
  CHECK_INCLUDE_FILE("pthread.h" CMAKE_HAVE_PTHREAD_H)
else()
  CHECK_INCLUDE_FILE_CXX("pthread.h" CMAKE_HAVE_PTHREAD_H)
endif()
if(CMAKE_HAVE_PTHREAD_H)

  #
  # We have pthread.h
  # Let's check for the library now.
  #
  set(CMAKE_HAVE_THREADS_LIBRARY)
  if(NOT THREADS_HAVE_PTHREAD_ARG)
    # Check if pthread functions are in normal C library.
    # If the pthread functions already exist in C library, we could just use
    # them instead of linking to the additional pthread library. We could
    # try to check any pthread symbol name, but here is an exception. If we
    # use clang asan build, we will find the pthread_create() symbol in the
    # libc(libasan). However, it doesn't have the full pthread implementation.
    # So, we can't assume that we have the pthread implementation in libc
    # using the pthread_create() checking here. Then, we turn to check the
    # pthread_kill() symbol instead.
    CHECK_SYMBOL_EXISTS(pthread_kill pthread.h CMAKE_HAVE_LIBC_PTHREAD_KILL)
    if(CMAKE_HAVE_LIBC_PTHREAD_KILL)
      set(CMAKE_THREAD_LIBS_INIT "")
      set(CMAKE_HAVE_THREADS_LIBRARY 1)
      set(Threads_FOUND TRUE)
    else()

      # Check for -pthread first if enabled. This is the recommended
      # way, but not backwards compatible as one must also pass -pthread
      # as compiler flag then.
      if (THREADS_PREFER_PTHREAD_FLAG)
         _check_pthreads_flag()
      endif ()

      _check_threads_lib(pthreads pthread_create CMAKE_HAVE_PTHREADS_CREATE)
      _check_threads_lib(pthread  pthread_create CMAKE_HAVE_PTHREAD_CREATE)
      if(CMAKE_SYSTEM_NAME MATCHES "SunOS")
          # On sun also check for -lthread
          _check_threads_lib(thread thr_create CMAKE_HAVE_THR_CREATE)
      endif()
    endif()
  endif()

  _check_pthreads_flag()
endif()

if(CMAKE_THREAD_LIBS_INIT OR CMAKE_HAVE_LIBC_PTHREAD_KILL)
  set(CMAKE_USE_PTHREADS_INIT 1)
  set(Threads_FOUND TRUE)
endif()

if(CMAKE_SYSTEM_NAME MATCHES "Windows")
  set(CMAKE_USE_WIN32_THREADS_INIT 1)
  set(Threads_FOUND TRUE)
endif()

if(CMAKE_USE_PTHREADS_INIT)
  if(CMAKE_SYSTEM_NAME MATCHES "HP-UX")
    # Use libcma if it exists and can be used.  It provides more
    # symbols than the plain pthread library.  CMA threads
    # have actually been deprecated:
    #   http://docs.hp.com/en/B3920-90091/ch12s03.html#d0e11395
    #   http://docs.hp.com/en/947/d8.html
    # but we need to maintain compatibility here.
    # The CMAKE_HP_PTHREADS setting actually indicates whether CMA threads
    # are available.
    CHECK_LIBRARY_EXISTS(cma pthread_attr_create "" CMAKE_HAVE_HP_CMA)
    if(CMAKE_HAVE_HP_CMA)
      set(CMAKE_THREAD_LIBS_INIT "-lcma")
      set(CMAKE_HP_PTHREADS_INIT 1)
      set(Threads_FOUND TRUE)
    endif()
    set(CMAKE_USE_PTHREADS_INIT 1)
  endif()

  if(CMAKE_SYSTEM MATCHES "OSF1-V")
    set(CMAKE_USE_PTHREADS_INIT 0)
    set(CMAKE_THREAD_LIBS_INIT )
  endif()

  if(CMAKE_SYSTEM MATCHES "CYGWIN_NT")
    set(CMAKE_USE_PTHREADS_INIT 1)
    set(Threads_FOUND TRUE)
    set(CMAKE_THREAD_LIBS_INIT )
    set(CMAKE_USE_WIN32_THREADS_INIT 0)
  endif()
endif()

set(CMAKE_REQUIRED_QUIET ${CMAKE_REQUIRED_QUIET_SAVE})
include(${CMAKE_CURRENT_LIST_DIR}/FindPackageHandleStandardArgs.cmake)
FIND_PACKAGE_HANDLE_STANDARD_ARGS(Threads DEFAULT_MSG Threads_FOUND)

if(THREADS_FOUND AND NOT TARGET Threads::Threads)
  add_library(Threads::Threads INTERFACE IMPORTED)

  if(THREADS_HAVE_PTHREAD_ARG)
    set_property(TARGET Threads::Threads
                 PROPERTY INTERFACE_COMPILE_OPTIONS "$<$<COMPILE_LANGUAGE:CUDA>:SHELL:-Xcompiler -pthread>"
                                                    "$<$<NOT:$<COMPILE_LANGUAGE:CUDA>>:-pthread>")
  endif()

  if(CMAKE_THREAD_LIBS_INIT)
    set_property(TARGET Threads::Threads PROPERTY INTERFACE_LINK_LIBRARIES "${CMAKE_THREAD_LIBS_INIT}")
  endif()
endif()