lock5.c

BeginningLinuxProgramming example7

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>


const char *test_file = "/tmp/test_lock";

int main() {
    int file_desc;
    struct flock region_to_lock;
    int res;

        /* open a file descriptor */
    file_desc = open(test_file, O_RDWR | O_CREAT, 0666);
    if (!file_desc) {
        fprintf(stderr, "Unable to open %s for read/write\n", test_file);
        exit(EXIT_FAILURE);
    }

    region_to_lock.l_type = F_RDLCK;
    region_to_lock.l_whence = SEEK_SET;
    region_to_lock.l_start = 10;
    region_to_lock.l_len = 5;
    printf("Process %d, trying F_RDLCK, region %d to %d\n", getpid(),
           (int)region_to_lock.l_start, (int)(region_to_lock.l_start + region_to_lock.l_len));
    res = fcntl(file_desc, F_SETLK, &region_to_lock);
    if (res == -1) {
        printf("Process %d - failed to lock region\n", getpid());
    } else {
        printf("Process %d - obtained lock region\n", getpid());
    }
   
    region_to_lock.l_type = F_UNLCK;
    region_to_lock.l_whence = SEEK_SET;
    region_to_lock.l_start = 10;
    region_to_lock.l_len = 5;
    printf("Process %d, trying F_UNLCK, region %d to %d\n", getpid(),
           (int)region_to_lock.l_start, (int)(region_to_lock.l_start + region_to_lock.l_len));
    res = fcntl(file_desc, F_SETLK, &region_to_lock);
    if (res == -1) {
        printf("Process %d - failed to unlock region\n", getpid());
    } else {
        printf("Process %d - unlocked region\n", getpid());
    }

    region_to_lock.l_type = F_UNLCK;
    region_to_lock.l_whence = SEEK_SET;
    region_to_lock.l_start = 0;
    region_to_lock.l_len = 50;
    printf("Process %d, trying F_UNLCK, region %d to %d\n", getpid(),
           (int)region_to_lock.l_start, (int)(region_to_lock.l_start + region_to_lock.l_len));
    res = fcntl(file_desc, F_SETLK, &region_to_lock);
    if (res == -1) {
        printf("Process %d - failed to unlock region\n", getpid());
    } else {
        printf("Process %d - unlocked region\n", getpid());
    }
    
    region_to_lock.l_type = F_WRLCK;
    region_to_lock.l_whence = SEEK_SET;
    region_to_lock.l_start = 16;
    region_to_lock.l_len = 5;
    printf("Process %d, trying F_WRLCK, region %d to %d\n", getpid(),
           (int)region_to_lock.l_start, (int)(region_to_lock.l_start + region_to_lock.l_len));
    res = fcntl(file_desc, F_SETLK, &region_to_lock);
    if (res == -1) {
        printf("Process %d - failed to lock region\n", getpid());
    } else {
        printf("Process %d - obtained lock on region\n", getpid());
    }

    region_to_lock.l_type = F_RDLCK;
    region_to_lock.l_whence = SEEK_SET;
    region_to_lock.l_start = 40;
    region_to_lock.l_len = 10;
    printf("Process %d, trying F_RDLCK, region %d to %d\n", getpid(),
           (int)region_to_lock.l_start, (int)(region_to_lock.l_start + region_to_lock.l_len));
    res = fcntl(file_desc, F_SETLK, &region_to_lock);
    if (res == -1) {
        printf("Process %d - failed to lock region\n", getpid());
    } else {
        printf("Process %d - obtained lock on region\n", getpid());
    }
    
    region_to_lock.l_type = F_WRLCK;
    region_to_lock.l_whence = SEEK_SET;
    region_to_lock.l_start = 16;
    region_to_lock.l_len = 5;
    printf("Process %d, trying F_WRLCK with wait, region %d to %d\n", getpid(),
           (int)region_to_lock.l_start, (int)(region_to_lock.l_start + region_to_lock.l_len));
    res = fcntl(file_desc, F_SETLKW, &region_to_lock);
    if (res == -1) {
        printf("Process %d - failed to lock region\n", getpid());
    } else {
        printf("Process %d - obtained lock on region\n", getpid());
    }

    printf("Process %d ending\n", getpid());    
    close(file_desc);
    exit(EXIT_SUCCESS);
}