task1.c

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>

// This is a silly glibc bug
#include <sys/syscall.h>
#define gettid() syscall(SYS_gettid)
#define THREAD_COUNT 10

void *writeToFile(void *threadID);

int main(int argc, char **argv) {
    int ret[THREAD_COUNT];
    pthread_t thread[THREAD_COUNT];

    // seed rand
    srand((unsigned int)time(NULL));

    // Create THREAD_COUNT threads
    for (int i = 0; i < THREAD_COUNT; i++) {
        ret[i] = pthread_create(&thread[i], NULL, writeToFile, &i);
        if (ret[i] != 0) {
            fprintf(stderr, "ERROR %d: Cant create thread\n", ret[i]);
            return EXIT_FAILURE;
        }
    }

    // Close a thread with a chance of 50%
    for (int i = 0; i < THREAD_COUNT; i++) {
        if (rand() % 2) pthread_cancel(thread[i]);
    }

    // Wait for finish
    for (int i = 0; i < THREAD_COUNT; i++) {
        ret[i] = pthread_join(thread[i], NULL);
        if (ret[i] != 0) {
            fprintf(stderr, "ERROR %d: Cant join thread\n", ret[i]);
            return EXIT_FAILURE;
        }
    }

    return EXIT_SUCCESS;
}

void cleanupHandler(void *arg) {
    // close file descriptor
    FILE *fp = (FILE *)arg;
    if (fp != NULL) {
        if (fclose(fp)) perror("cleanuphander");
    }
}

void *writeToFile(void *threadID) {
    int waitTime = 0;
    char filename[12];
    FILE *fptr = NULL;

    // Sleep between 0 - 3 Seconds
    waitTime = rand() % 4;
    sleep(waitTime);

    // format filename
    sprintf(filename, "Thread%d.txt", *(int *)threadID);

    /*	will called when thread is canceled, calls pthread_exit or
    pthread_cleanup_pop is executed with non-zero EXECUTE argument */
    pthread_cleanup_push(cleanupHandler, fptr);

    // try to open a file
    fptr = fopen(filename, "rb+");
    if (fptr == NULL) {
        // file does not exist, create it
        fptr = fopen(filename, "wb");
        if (fptr == NULL) {
            printf("Disc full or no permission\n");
            return NULL;
        }
    }

    // Write file
    fprintf(fptr, "%d\n", (int)gettid());

    // call cleanup handler
    pthread_cleanup_pop(1);

    // close
    fclose(fptr);

    return NULL;
}