Cmake在Maverick上无法与OpenMP一起使用。

Question

我正在使用OpenMP编写并行代码。以下是我在CMakeLists中使用的一部分。

FIND_PACKAGE( OpenMP REQUIRED)
    if(OPENMP_FOUND)
    message("OPENMP FOUND")
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${OpenMP_EXE_LINKER_FLAGS}")
    endif()

然而，当我们执行 cmake .. 时，似乎找不到 OpenMP 包，我收到了以下错误提示：

Try OpenMP C flag = [ ]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP C flag = [-fopenmp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP C flag = [/openmp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP C flag = [-Qopenmp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP C flag = [-openmp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP C flag = [-xopenmp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP C flag = [+Oopenmp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP C flag = [-qsmp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP C flag = [-mp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP CXX flag = [ ]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP CXX flag = [-fopenmp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP CXX flag = [/openmp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP CXX flag = [-Qopenmp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP CXX flag = [-openmp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP CXX flag = [-xopenmp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP CXX flag = [+Oopenmp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP CXX flag = [-qsmp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
-- Try OpenMP CXX flag = [-mp]
-- Performing Test OpenMP_FLAG_DETECTED
-- Performing Test OpenMP_FLAG_DETECTED - Failed
CMake Error at /opt/local/share/cmake-3.3/Modules/FindPackageHandleStandardArgs.cmake:148 (message):
  Could NOT find OpenMP (missing: OpenMP_C_FLAGS OpenMP_CXX_FLAGS)

这里是CMakeLists.txt。

cmake_minimum_required(VERSION 2.6)

#Declaration du projet

project(MYfirstcamke)

set(EXECUTABLE_OUTPUT_PATH bin/${CMAKE_BUILD_TYPE})

#Inclusion de opencv

include_directories(/usr/local/include/)

link_directories(/usr/local/lib)

FIND_PACKAGE( OpenMP REQUIRED)
if(OPENMP_FOUND)
message("OPENMP FOUND")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${OpenMP_EXE_LINKER_FLAGS}")
endif()

find_package(PCL 1.2 REQUIRED)
include_directories(${PCL_INCLUDE_DIRS})
link_directories(${PCL_LIBRARY_DIRS})
add_definitions(${PCL_DEFINITIONS})

file(

    GLOB_RECURSE

    source_files

    src/*


)
#declaration de l'executable

add_executable(

my_executable

${source_files}

)
#Configuration de l'edition de lien.
target_link_libraries(

my_executable opencv_core  opencv_imgproc opencv_video opencv_highgui ${PCL_LIBRARIES}


)

我该如何修复这个问题？我确定已经安装了openMPI，并且它位于/opt/local/include目录下。

- Jeanne

---

你确定你没有混淆OpenMP和OpenMPI吗？我看到你使用了两个标签，并且在帖子末尾提到了OpenMPI。但是这两者完全不同。OpenMP是多线程并行语言扩展的标准，而OpenMPI是用于消息传递的MPI标准的实现。你需要哪一个？ - Gilles

OpenMP不是一个软件包，而是编译器的一个组成部分。很久以前，Xcode曾经提供过支持OpenMP的GCC版本。然后，苹果转向了Clang，但它没有OpenMP支持，至少在随Xcode一起发布的版本中没有。你应该从源代码或使用Homebrew/MacPorts/其他方式安装GCC。 - Hristo Iliev

@Gilles，也许我混淆了OpenMP和OpenMPI。我认为OpenMP已经被弃用并变成了OpenMPI。 - Jeanne

@HristoIliev，我已经安装了GCC，但是我该如何在CMakeLists.txt中指定编译器。我已经将CMakeLists.txt文件添加到我的问题中。 - Jeanne

我不太理解CMake，但在运行CMake之前，可能需要执行类似于export CC=gcc-4.9; export CXX=g++-4.9的操作。请将gxx-4.9替换为相应编译器的实际名称。 - Hristo Iliev

Answer 1

OpenMP和MPI是完全不同的东西。

OMP需要编译器支持，在OS X上需要通过Homebrew获取。（你也可以通过Homebrew安装MPI，这很方便）。

brew install clang-omp

在安装了clang-omp之后，您可以通过以下方式调用CMake来使用该编译器。

CC=clang-omp CXX=clang-omp++ cmake <insert your normal cmake parameters here>

- Jonathan Howard

---

根据http://openmp.llvm.org/的说法，

“随着Clang 3.8.0的发布，Clang默认启用了OpenMP 3.1支持，因此OpenMP运行时作为Clang构建的正常部分构建”

我不明白为什么我仍然需要安装“clang-omp”，您能否解释一下原因？另一个问题是，“clang-omp”公式要求使用与“llvm”公式不同版本的clang（和“compiler-rt”等），那么我该怎么做才能使事情变得正确？ - squid

我正在尝试使用CMake 3.7和clang 4.0，但我的find_package(OpenMP REQUIRED)失败了。 - David Doria

Answer 2

一种解决方案是安装并使用GNU GCC。假设您已经安装了它或将通过HomeBrew进行安装brew install gcc：

if(APPLE)
  set(CMAKE_C_COMPILER "/usr/local/bin/gcc-9")
  set(CMAKE_CXX_COMPILER "/usr/local/bin/g++-9")
  set(CMAKE_Fortran_COMPILER "/usr/local/bin/gfortran")
endif()

-9版本可能会在未来发生变化。

- Foad S. Farimani

Answer 3

除了上面的答案，你还可以通过Homebrew安装gcc-5/g++-5。纯粹的gcc-5安装（没有Clang包装器）将支持OpenMP，并且CMake应该能够通过Find_Package来检测到它。

- Sidharth N. Kashyap