CMake/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.
#]=======================================================================]

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

# simple pthread test code
set(PTHREAD_C_CXX_TEST_SOURCE [====[
#include <pthread.h>

void* test_func(void* data)
{
  return data;
}

int main(void)
{
  pthread_t thread;
  pthread_create(&thread, NULL, test_func, NULL);
  pthread_detach(thread);
  pthread_join(thread, NULL);
  pthread_atfork(NULL, NULL, NULL);
  pthread_exit(NULL);

  return 0;
}
]====])

# 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.
    # We list some pthread functions in PTHREAD_C_CXX_TEST_SOURCE test code.
    # If the pthread functions already exist in C library, we could just use
    # them instead of linking to the additional pthread library.
    if(CMAKE_C_COMPILER_LOADED)
      CHECK_C_SOURCE_COMPILES("${PTHREAD_C_CXX_TEST_SOURCE}" CMAKE_HAVE_LIBC_PTHREAD)
    elseif(CMAKE_CXX_COMPILER_LOADED)
      CHECK_CXX_SOURCE_COMPILES("${PTHREAD_C_CXX_TEST_SOURCE}" CMAKE_HAVE_LIBC_PTHREAD)
    endif()
    if(CMAKE_HAVE_LIBC_PTHREAD)
      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 ()

      if(CMAKE_SYSTEM MATCHES "GHS-MULTI")
        _check_threads_lib(posix pthread_create CMAKE_HAVE_PTHREADS_CREATE)
      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)
  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()