Question

I am trying to write a program which gets input files and prints included items into the screen by threads. However, last thread doesn’t give any output unexpectedly. I couldn’t figure out what the problem is. I am waiting for your help.

Each thread gets 3 parameters :inputFile1, inputFile2 and targetBuf(lets say it is sequence number.) Files are sorted, I just simply try to print their union in order. Only positive numbers are printed.

Command line : merge N outfile file1 file2 file3 …. fileN
N is the number of input files.

If I give 2 input files (means 1 thread), it works. If I give 4 files, then 1st thread give output, 2nd one does not. If I give 6 input files, then 1st and 2nd threads give output but 3rd doesn’t.

There are two structs in header file. I pasted them below.

//thread information
struct threadInfo{
    pthread_t tid;
    pthread_attr_t attr;
};
//Beginning thread input
struct beginThreadInput{
    FILE **inputFile1, **inputFile2;
    int targetBuf;
};
typedef struct threadInfo THREADINFO;
typedef struct beginThreadInput BEGINT_INPUT;

Main File Code:

      #include <stdio.h>
      #include <unistd.h>
      #include <stdlib.h>
      #include <pthread.h>
      #include <semaphore.h>
      #include <sys/types.h>
      #include <errno.h>
      #include <sys/mman.h>
      #include <sys/stat.h>
      #include <unistd.h>
      #include <fcntl.h>    //for O_ constants
      #include <sys/stat.h>
      #include <pthread.h> /* thread library */

      #include "merge.h"



      int main(int argc, char** argv){
        int i, k, N;

        /***FILE INITIALIZATION***/
        FILE *output;
        N = atoi(argv[1]);
        output = fopen(argv[2], "w");
        FILE **inputFileList = ((FILE**)malloc (N * sizeof(FILE*)));
        printf("int N is %d\n", N);
        for(i = 0; i<N; i++){
            inputFileList[i] = fopen(argv[i + 3], "r");
        }
        //START THREADS
        BEGINT_INPUT **threadInputList = ((BEGINT_INPUT**) malloc ( (N/2)*        sizeof(BEGINT_INPUT*)));
        THREADINFO **threadInfoList = ((THREADINFO**) malloc ( (N/2) *          sizeof(THREADINFO*)));
        for(i = 0; i< N/2 ; i++){
            threadInputList[i] = (BEGINT_INPUT *) malloc (sizeof(BEGINT_INPUT));
            threadInfoList[i] = (THREADINFO *) malloc (sizeof(THREADINFO));
        }
        pthread_t tid;
        pthread_attr_t attr;
        for(i = 0, k = 0; i < (N/2); i++){


            threadInputList[i]->inputFile1 = &(inputFileList[k]);
            threadInputList[i]->inputFile2 = &(inputFileList[++k]);
            threadInputList[i]->targetBuf = i;
            pthread_attr_init(&(threadInfoList[i]->attr));
            pthread_create(&(threadInfoList[i]->tid), &(threadInfoList[i]->attr), runBeginningThreads, (void*)threadInputList[i]);

        }
        pthread_join((threadInfoList[[(N/2)-1]]->tid), NULL);
        for(i = 0; i<N; i++){
            fclose(inputFileList[i]);
        }

      }

      void *runBeginningThreads(void *input){

        BEGINT_INPUT *myInput = (BEGINT_INPUT *)input;
        int first = -1, second = -1, iseof;
        printf("Thread number %d\n", myInput->targetBuf);
        while((second > -2) && (first > -2)){
            //read integer values from files
            if(first == -1){
                iseof = fscanf(*(myInput->inputFile1), "%d", &first);
                if(iseof == EOF){
                    first = -2;     //means end of file
                }
                else if(first < 0)
                    first = -1;     //means waiting for an integer
            }
            if(second == -1){
                iseof = fscanf(*(myInput->inputFile2), "%d", &second);
                if(iseof == EOF){
                    second = -2;
                }
                else if(second < 0)
                    second = -1;
            }
            //print smaller one
            if((first != -1) && (second != -1)){
                if(((first < second) || (second == -2)) && (first != -2)){
                    printf("%d\n", first);
                    first = -1;
                }
                else if(second != -2){
                    printf("%d\n", second);
                    second = -1;
                }
            }
        }
      }

Answer 1

I solve my question in the following way. As it is seen above, I open the files in main function, then pass them into corresponding threads. I have changed this way and passed the names of the files into threads and open related files in them.

Additionally, while passing files, I was making mistakes, its code is below

 threadInputList[i]->inputFile1 = &(inputFileList[k]);
 threadInputList[i]->inputFile2 = &(inputFileList[++k]);

This lines are run in a loop. This causes an input sequence like the following ([0,1], [1,2], [2,3], [3,4] …) becuase I increment k only one time.However, each thread takes two of inputFiles. So the correct code is this:

 threadInputList[i]->inputFile1 = &(inputFileList[k++]);
 threadInputList[i]->inputFile2 = &(inputFileList[k++]);

I want to point out an issue. I fixed this code for file names, not FILE pointer variables as it is posted there. But to make it clear, I fixed the bug on a code posted there. Thanks for your help, everybody