如何在C ++程序中使用openmp [英] how to use openmp in a c++ program
问题描述
我想使用OpenMP来并行化c ++程序中的某些功能.
I would like to use OpenMP to parallelize some of my functions in a c++ program.
我在具有4核的intel i5上使用ubuntu 12.04. 但是，按照某些步骤操作后，我看不到性能有任何改善.我可以看到只使用了一个CPU内核. (ubuntu中的系统监视器)
I am using ubuntu 12.04, on intel i5 with 4 cores. But after following certain steps, I do not see any improve in performance. I could see that only one CPU core is being used. (system monitor in ubuntu )
我做了什么.
添加了#include <omp.h>
在for循环之前添加了这两行
added these two lines before a for loop
omp_set_num_threads(4);
#pragma omp parallel for
在CMakeLists.txt中，
in CMakeLists.txt,
我添加了target_link_libraries (executable -fopenmp -lgomp ${PCL_LIBRARIES} )
I added target_link_libraries (executable -fopenmp -lgomp ${PCL_LIBRARIES} )
您能帮我获得并行性吗?
Can you please help me in getting the parallelism ?
谢谢！
推荐答案
如@Mikael Persson所述，我从目标链接库中删除了-fopenmp并添加了
find_package(OpenMP)
if (OPENMP_FOUND)
set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}")
set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
endif()
As mentioned by @Mikael Persson , I removed -fopenmp from the target link libraries and added
find_package(OpenMP)
if (OPENMP_FOUND)
set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}")
set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
endif()
此功能正常.
出现错误r *** double free or corruption (!prev): 0x00007ff424006b20 ***是因为在for循环中，我试图使用push_back()函数加载堆栈，并且索引取决于for循环索引.我认为这就是问题的原因.
The error r *** double free or corruption (!prev): 0x00007ff424006b20 *** was arising because in the for loop, i was trying to use push_back() function to load a stack and the index was dependant on the for loop index. I think that was the cause of the problem.
我学到了另一件事，即可以嵌套用于循环，并且OMP如果变量是独立的并且可以产生有效结果，则可以正常工作
I learnt one more thing that one can have nested for loops and OMP can work without errors if their variables are independent and produce valid results
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