Easiest way to make basic OpenMP like library

Question

I would like to make a basic library with some very basic features of OpenMP. For example, just to be able to write a code like below. I wonder how I can use LLVM and pthreads to accomplish this. I guess there are two steps:

1. Preprocessing to figure out the parallel task (parallel vs parallel-for)
2. Convert appropriate code blocks to a void* function needed for pthreads
3. Automation to create, run and join threads

Example code:

#Our_Own parallel
{
   printf("hello");
}

#Our_Own parallel for
for (int i =0; i < 1000; i++)
{
     printf(i);
}

Answer 1

DISCLAIMER: This is a very hard task, and there are many hidden tasks involved (how to access variables and set up their sharing attributes, implicit barriers, synchronization, etc.) I do not claim that you can solve all of them using the idea described below.

If you use a (python) script to preprocess your code, here is a very minimal example how to start in C language (C++ may be a bit easier because of lambda functions).

Use macro definitions (preferably put them in a header file) :

// Macro definitions (in own.h)
#define OWN_PARALLEL_BLOCK_START(f) \
void *f(void * data) \
{    \
    
#define OWN_PARALLEL_BLOCK_END \
    return NULL; \
}  

#define OWN_PARALLEL_MAIN(f) \
{ \
    int THREAD_NUM=4;  \
    pthread_t thread_id[THREAD_NUM];  \
    for(int i=0;i<THREAD_NUM;i++) {  \
        pthread_create(&thread_id[i], NULL, f, NULL); \
    } \
    for(int i=0;i<THREAD_NUM;i++) { \
       pthread_join(thread_id[i], NULL); \
    } \
}

Your (python) script should convert this:

int main(){
    #pragma own parallel
    {
       printf("Hello word\n");
    }
}

to the following:

OWN_PARALLEL_BLOCK_START(ThreadBlock_1)
{
   printf("Hello word\n");
}
OWN_PARALLEL_BLOCK_END

int main(){
   OWN_PARALLEL_MAIN(ThreadBlock_1)    
}

Check it on Compiler Explorer