CODEWITHSUNDEEP
clinuxmultithreading
Sebastian Rockefeller
Sebastian Rockefeller

Reputation: 549

Read line by line from a file and create a thread for every line in a file in c programming in Linux

I'm trying to create a thread for every line in a file and pass to a thread function this line from a file as an argument in c programming in Linux.

Here is my code:

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>

/* perform_work function args struct */
typedef struct {
    char arg_1[20];
} arg_struct;

/* counter fo threads */
int count = 0;

/* function to execute in every thread */
void *perform_work(void *argument)
{
   arg_struct *actual_args = argument;
   printf("\nthread processing done, arg_1 = %d\n", *actual_args->arg_1);
   ++count;
   printf("Thread number = %d\n", count);

   return NULL;
}

/* main function */
int main(void)

{
    int lines_allocated = 128;
    int max_line_len = 100;

    /* allocate lines of text */
    char **words = (char **)malloc(sizeof(char*)*lines_allocated);
    if (words==NULL) {
        fprintf(stderr,"Out of memory (1).\n");
        exit(1);
    }

    FILE *fp = fopen("file.txt", "r");
    if (fp == NULL) {
        fprintf(stderr,"Error opening file.\n");
        exit(2);
    }

    int i;
    for (i=0;1;i++) {
        int j;

        /* have we gone over our line allocation? */
        if (i >= lines_allocated) {
            int new_size;

            /* Double our allocation and re-allocate */
            new_size = lines_allocated*2;
            words = (char **)realloc(words,sizeof(char*)*new_size);
            if (words==NULL){
                fprintf(stderr,"Out of memory.\n");
                exit(3);
            }
            lines_allocated = new_size;
        }

        /* allocate space for the next line */
        words[i] = malloc(max_line_len);
        if (words[i]==NULL)
            {
            fprintf(stderr,"Out of memory (3).\n");
            exit(4);
            }
        if (fgets(words[i],max_line_len-1,fp)==NULL)
            break;

        /* get rid of CR or LF at end of line */
        for (j=strlen(words[i])-1;j>=0 && (words[i][j]=='\n' || words[i][j]=='\r');j--)
            ;
        words[i][j+1]='\0';
    }

    /* close file */
    fclose(fp);

    pthread_t threads[i];
    int thread_args[i];
    int result_code, index;
    int *ptr[i];

    /* create all threads one by one */
    for (index = 0; index < i; ++index) {
        arg_struct *args = malloc(sizeof *args);
        strcpy(args->arg_1, words[index]);

        result_code = pthread_create(&threads[index], NULL, perform_work, args);
        assert(0 == result_code);
    }

    /* wait for each thread to complete */
    for (index = 0; index < i; ++index) {
      // block until thread 'index' completes
      result_code = pthread_join(threads[index], (void**)&(ptr[index]));
      //printf("In main: thread %d has completed\n", index);
      assert(0 == result_code);
    }

    printf("In main: All threads completed successfully\n");

    int j;
    for(j = 0; j < i; j++)
        printf("%s\n", words[j]);

    /* good practice to free memory */
    for (;i>=0;i--)
        free(words[i]);
    free(words);


    return 0;
}

I'm stuck on this code. It works but threads function get some strange args value.

Output:

thread processing done, arg_1 = 51
Thread number = 1

thread processing done, arg_1 = 50
Thread number = 2

thread processing done, arg_1 = 55
Thread number = 3

thread processing done, arg_1 = 49
Thread number = 4

thread processing done, arg_1 = 53
Thread number = 5

thread processing done, arg_1 = 52
Thread number = 6

thread processing done, arg_1 = 54
Thread number = 7

thread processing done, arg_1 = 56
Thread number = 8

thread processing done, arg_1 = 57
Thread number = 9

thread processing done, arg_1 = 49
Thread number = 10

thread processing done, arg_1 = 49
Thread number = 11

thread processing done, arg_1 = 49

thread processing done, arg_1 = 49
Thread number = 13

thread processing done, arg_1 = 49
Thread number = 14

thread processing done, arg_1 = 49
Thread number = 15

thread processing done, arg_1 = 49
Thread number = 16

thread processing done, arg_1 = 49
Thread number = 17

thread processing done, arg_1 = 49
Thread number = 18

thread processing done, arg_1 = 50
Thread number = 19

thread processing done, arg_1 = 49
Thread number = 20
Thread number = 12
In main: All threads completed successfully
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

But the file contains this lines:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

I want threads function args would be line by line read from a file.

In the code above I read from a file to array first and then for every line in an array create a thread. Is it possible to create threads in a loop when reading a file without additional array? If yes, how? If not, what to do if the lines would be to much? Help me please.

Upvotes: 0

Views: 2107

Answers (1)

Iłya Bursov
Iłya Bursov

Reputation: 24229

I've noticed two problems:

printf("\nthread processing done, arg_1 = %d\n", *actual_args->arg_1);

should be:

printf("\nthread processing done, arg_1 = %s\n", actual_args->arg_1);

as we're printing string, not code of first symbol

for (index = 0; index < i; ++index) {
    arg_struct *args = malloc(sizeof *args);
    strcpy(args->arg_1, words[index]);

    result_code = pthread_create(&threads[index], NULL, perform_work, args);
    assert(0 == result_code);
}

should be:

arg_struct *args = malloc(sizeof(arg_struct)*i);
for (index = 0; index < i; ++index) {
    strcpy(args[index].arg_1, words[index]);
    result_code = pthread_create(&threads[index], NULL, perform_work, &args[index]);
    assert(0 == result_code);
}

Upvotes: 1

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