文件读取加锁：

#include <stdio.h>  
#include <stdlib.h>  
#include <fcntl.h>  
#include <unistd.h>  
#include <sys/stat.h>  
#include <sys/file.h>  
  
#define LOCK_FILE "/root/priv/cjson/test.lock"
#define DATA_FILE "json.txt"  
  
int main() {  
    int fd_lock, fd_data;  
    struct flock lock;  
  
    // 创建文件锁  
    fd_lock = open(LOCK_FILE, O_WRONLY | O_CREAT, 0644);  
    if (fd_lock == -1) {  
        perror("open lock file");  
        exit(EXIT_FAILURE);  
    }  
  
    // 设置独占锁  
    lock.l_type = F_WRLCK;  
    lock.l_start = 0;  
    lock.l_whence = SEEK_SET;  
    lock.l_len = 0; // 锁定整个文件  
    if (fcntl(fd_lock, F_SETLKW, &lock) == -1) {  
        perror("fcntl lock");  
        close(fd