共享锁和排他锁 linux

# 使用fcntl系统调用实现共享锁和排他锁

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

int main() {
    int fd = open("example.txt", O_RDWR);
    if (fd == -1) {
        perror("open");
        return 1;
    }

    // 获取共享锁
    struct flock fl;
    fl.l_type = F_RDLCK;  // 共享锁
    fl.l_whence = SEEK_SET;
    fl.l_start = 0;
    fl.l_len = 0;
    if (fcntl(fd, F_SETLKW, &fl) == -1) {
        perror("fcntl");
        close(fd);
        return 1;
    }

    // 读取文件内容
    char buffer[100];
    read(fd, buffer, sizeof(buffer));
    printf("Read: %s\n", buffer);

    // 释放共享锁
    fl.l_type = F_UNLCK;
    if (fcntl(fd, F_SETLK, &fl) == -1) {
        perror("fcntl");
        close(fd);
        return 1;
    }

    // 获取排他锁
    fl.l_type = F_WRLCK;  // 排他锁
    if (fcntl(fd, F_SETLKW, &fl) == -1) {
        perror("fcntl");
        close(fd);
        return 1;
    }

    // 写入文件内容
    const char *new_content = "New content";
    write(fd, new_content, strlen(new_content));

    // 释放排他锁
    fl.l_type = F_UNLCK;
    if (fcntl(fd, F_SETLK, &fl) == -1) {
        perror("fcntl");
        close(fd);
        return 1;
    }

    close(fd);
    return 0;
}