如何将OpenMP指令(#pragmas)包装为函数或类函数宏？

2023年4月1日 222次阅读

我正在尝试将OpenMP与另一种发出C代码的语言(C代码生成器)进行交互.从我的角度来看(我不是另一种语言的设计者),通过调用C函数或类似函数的宏而不是直接使用#pragma或_Pragma来实现这一点是最简单的.我对C预处理器没有太多经验,但是我在维基百科上找到了一个简单的例子,以不令人满意的方式工作.这是原始的C示例：

#include <omp.h>
#include <stdio.h>
#include <stdlib.h>

int main (int argc, char *argv[]) {
  int th_id, nthreads;
  #pragma omp parallel private(th_id)
  {
    th_id = omp_get_thread_num();
    printf("Hello World from thread %d\n", th_id);
    #pragma omp barrier
    if ( th_id == 0 ) {
      nthreads = omp_get_num_threads();
      printf("There are %d threads\n",nthreads);
    }
  }
  return EXIT_SUCCESS;
}

现在我在这里创建一个宏(pragma_omp_parallel_private)来做我想要的事情：

#include <omp.h>
#include <stdio.h>
#include <stdlib.h>

#define STR(x) #x
#define STRINGIFY(x) STR(x) 
#define omp_par_pri STRINGIFY(omp parallel private)

char omp_test[] = omp_par_pri;
#define pragma_omp_parallel_private(thread_id)        \
  _Pragma(STRINGIFY(omp parallel private ## (thread_id)))

int main (int argc, char *argv[]) {
  int th_id, nthreads;

  // #pragma omp parallel private(th_id)
  pragma_omp_parallel_private(th_id)
  {
    th_id = omp_get_thread_num();
    printf("Hello World from thread %d\n", th_id);
    #pragma omp barrier
    if ( th_id == 0 ) {
      nthreads = omp_get_num_threads();
      printf("There are %d threads\n",nthreads);
    }
  }
  return EXIT_SUCCESS;
}

预处理器将发出错误,但如果我实际编译预处理的代码,它将按预期工作.有没有更合法的方法来实现这一点(更不用说在大多数构建管道中不会导致构建错误的方法)？

$gcc -E -fopenmp wikiHello.c > wikiHello_pp.c
wikiHello.c:11:34: error: pasting "private" and "(" does not give a valid preprocessing token
   _Pragma(STRINGIFY(omp parallel private ## (thread_id)))
                                  ^
wikiHello.c:17:3: note: in expansion of macro ‘pragma_omp_parallel_private’
   pragma_omp_parallel_private(th_id)
   ^
$gcc -fopenmp wikiHello_pp.c

$./a.exe
Hello World from thread 3
Hello World from thread 6
Hello World from thread 4
Hello World from thread 7
Hello World from thread 1
Hello World from thread 5
Hello World from thread 2
Hello World from thread 0
There are 8 threads

最佳答案 在将它转换为字符串文字之前,我会将该pragma连接起来.像这样的东西：

#include <omp.h>
#include <stdio.h>
#include <stdlib.h>

#define STR(x) #x
#define STRINGIFY(x) STR(x) 
#define CONCATENATE(X,Y) X ( Y )

#define pragma_omp_parallel_private(x) \
  _Pragma( STRINGIFY( CONCATENATE(omp parallel private,x) ) )

int main (int argc, char *argv[]) {
  int th_id, nthreads;

  // #pragma omp parallel private(th_id)
  pragma_omp_parallel_private(th_id)
  {
    th_id = omp_get_thread_num();
    printf("Hello World from thread %d\n", th_id);
    #pragma omp barrier
    if ( th_id == 0 ) {
      nthreads = omp_get_num_threads();
      printf("There are %d threads\n",nthreads);
    }
  }
  return EXIT_SUCCESS;
}
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