C: merging temp files created with tmpfile() function with multithreading

Question

I have n files and my program needs to merge the contents of all into an one file using threads and temp files (have to use tmpfile()). When creating a thread it has to merge 2 files into a temp file (temp1) then another thread will merge the next 2 files into another temp file (temp2) and so on, then in the next level another thread should merge temp1 with temp2 into another temp file.

alt text

I was thinking in creating an array of file names passing it to pthread_create as argument, and the function should return the array modified too but i can't figure how to get the tempfile name. Will be something like this:

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

int n = argc -1;

char *files_arr[n];

pthread_t threads[n-1];

}

    for (int i=0; i < argc; i++)

    {
       pthread_create (&threads[i], NULL, temp_merge, (void *) &files_arr);
    }
}//end main

void *temp_merge (void *arg){

    char *myarray[];
    myarray = (char *) arg;
    FILE *f1, *f2, *tf;
    tf = tmpfile();

    //code to merge f1 and f2 into tf, f1 and f2 could be temp files created before

     pthread_exit((void*) myarray); //Do I lose the temp file using pthread_exit? 
}

The question is: How can I access to a temp file openned before with tmp() in a previous thread to generate new temporary files?

"i can't figure how to get the tempfile name." - you can't, in general That's the point of tmpfile — The Archetypal Paul
That's right Paul, so how do I "store" these temp files to read them later? — g0d1anier
create an array of saved names. after each step, merge those files into the new files (saving those names as you go). the word 'recursive' comes to mind here ;) — KevinDTimm
if you mean by "later" another run of this or another program: you cannot, because tmpfile() deletes the file after completion; — Peter Miehle
@Kevin the problem is i can't "save" the names of the temp files using tmpfile() and i thought in recursion but i think if i use it its gonna do all in one thread (i need a thread for each merging). @Peter when i say "later" i mean in a next thread at the same program — g0d1anier

Oliver Charlesworth Oliver Charlesworth · Accepted Answer · 2010-11-01T14:55:42

1

votes

Could you use tmpnam() instead of tmpfile(), and manually open/close/delete files as necessary?

C: merging temp files created with tmpfile() function with multithreading

2 Answers