C Thread doesn't run in linux terminal-CodePudding

My program has to increment a counter strictly alternatively using 2 threads and synchronizing them using a pipe file. I know it doesn't really make sense but it's a university task. The problem works if I run it with CodeBlocks for instance but it doesn't print anything when I execute the program from linux terminal and I can't figure out why. Any idea? Here is my code:

#include <stdlib.h>
#include <pthread.h>
#include <wait.h>
#include <unistd.h>
#include <string.h>

int contor;
int fd[2];

void* thread_function(void* arg) {
    int* th = (int*)arg;
    char x = 'x';

    while(1)
    {
        if (*th == 0 && contor % 2 == 0 && contor < 100) {
            close(fd[0]);
            write(fd[1], &x, 1);
            contor  ;
            printf("Counter: %d incremented by thread: %ld\n", contor, pthread_self());
            sleep(0);
            if (contor >= 100)
            {
                pthread_exit(NULL);
            }

        } else if (*th == 1 && contor % 2 == 1 && contor < 100){
            close(fd[1]);
            read(fd[0], &x, 1);

            contor  ;
            printf("Counter: %d incremented by thread: %ld\n", contor, pthread_self());

            if (contor >= 100)
            {
                pthread_exit(NULL);
            }
        }
        if (contor >= 100)
            {
                pthread_exit(NULL);
            }

    }
}

void main(int argc, char** argv) {
    int tr1 = 0;
    int tr2 = 0;
    pthread_t t1, t2;

    int th0 = 0;


    pipe(fd);

    tr1 = pthread_create(&t1, NULL, &thread_function, (void*)&th0);
    if (tr1) {
        printf("Error creating thread #1!");
    }

    int th1 = 1;

    tr2 = pthread_create(&t2, NULL, &thread_function, (void*)&th1);
    if (tr2) {
        printf("Error creating thread #2!");
    }

    pthread_join(t1, NULL);
    pthread_join(t2, NULL);
}

I compile the file using: gcc -o ex.exe ex.c -lpthread I execute the executable using: ./ex.exe

CodePudding user response：

File descriptors are shared by all the threads of a process. One of your threads is closing one end of the pipe (fd[0]) and writing the other end of the pipe (fd[1]). Your other thread is closing the other end of the pipe (fd[1]) and reading the other end of the pipe (fd[0]). Also, they are being closed multiple times in a while loop.

Getting rid of the close(fd[0]) and close(fd[1]) calls in thread_function will help a bit. There may be other problems in thread_function because the program stopped producing output after the counter reached the value 3 when I tried it.

Hint: Use two pipes.