1. 注意fcntl()参数cmd 的正确使用
F_GETFL 用于测试锁使用
F_SETFL 无阻塞设置锁 fcntl()会尝试几次后，如果失败直接返回-1
F_SETLKW 阻塞设置锁 fcntl()会尝试后，如果失败会被系统挂起来，直到收到解锁的信号再去执行
2. 测试锁的时候 struct flock lock结构体成员 中的l_stype 需要设置为F_WRLCK 其它F_UNLCK,F_RDLCK会有问题
3.struct flock lock 成员使用
测试或锁 整个文件怎样设置
l_whence = SEEK_SET
l_start = 0;
l_len = 0; 如果l_len为0 表示 从start 开始一直到文件最后EOF
struct flock {
...
short l_type; /* Type of lock: F_RDLCK,
F_WRLCK, F_UNLCK */
short l_whence; /* How to interpret l_start:
SEEK_SET, SEEK_CUR, SEEK_END */
off_t l_start; /* Starting offset for lock */
off_t l_len; /* Number of bytes to lock */
pid_t l_pid; /* PID of process blocking our lock
(F_GETLK only) */
...
};
5.程序自己测试自己的锁， 测试后肯定是无锁状态
6.程序如果设置的两个区间 连续而且锁的性质一样，系统会自动地将两个锁合并成一个锁
7.更多可以参考以下牛人
http://zhuyunxiang.blog.51cto.com/653596/132548
执行结果：
在另一个终端执行
main.c
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#include"setlock.h" #include<stdio.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> int main(void) { int fd = open("./src", O_RDWR|O_CREAT, S_IRWXU|S_IRWXG|S_IXOTH); check_lock(fd,0,10); check_lock(fd,11,20); set_read_lock(fd,0,10); set_write_lock(fd,11,20); sleep(15); unlock(fd,0,10); unlock(fd,11,20); return 0; } setlock.h
#ifndef SETLOCK_H #define SETLOCK_H void check_lock(int fd,int start,int len); void unlock(int fd,int start,int len); void set_read_lock(int fd,int start,int len); void set_write_lock(int fd,int start,int len); #endif // end SETLOCK_H setlock.c
#include <unistd.h> #include <fcntl.h> #include<stdio.h> #include<stdlib.h> #include <sys/types.h> #include<stdbool.h> void check_lock(int fd,int start,int len) { struct flock lock; lock.l_type = F_WRLCK; lock.l_start = start; lock.l_whence = SEEK_SET; lock.l_len = start; printf("check_lock------\n"); if((fcntl(fd, F_GETLK, &lock)) == -1) { printf("1-check_lock: fcntl error\n"); exit(1); } switch(lock.l_type) { case F_RDLCK: { printf("[%d]:FRDLCK From %d To %d\n", lock.l_pid, start, len); break; } case F_WRLCK: { printf("[%d]:F_WRLCK From %d To %d\n", lock.l_pid, start, len); break; } case F_UNLCK: { printf("F_UNLCK\n"); break; } default: { printf("2-check_lock: fcntl error"); break; } } } void set_read_lock(int fd,int start,int len) { printf("set_read_lock------\n"); struct flock lock; lock.l_type = F_RDLCK; lock.l_start = 0; lock.l_whence = SEEK_SET; lock.l_len = 0; if((fcntl(fd, F_SETLKW, &lock)) == -1) { printf("set_lock: fcntl error\n"); exit(1); } else { printf("[%d] set readlock From %d To %d\n", getpid(), start, len); } } void set_write_lock(int fd,int start,int len) { printf("set_write_lock------\n"); struct flock lock; lock.l_type = F_WRLCK; lock.l_start = start; lock.l_whence = SEEK_SET; lock.l_len = len; if((fcntl(fd, F_SETLKW, &lock)) == -1) { printf("set_lock: fcntl error\n"); exit(1); } else { printf("[%d] set writelock From %d To %d\n", getpid(), start, len); } } bool unlock(int fd,int start,int len) { printf("unlock------\n"); struct flock lock; lock.l_type = F_UNLCK; lock.l_start = start; lock.l_whence = SEEK_SET; lock.l_len = len; if((fcntl(fd, F_SETLK, &lock)) == -1) { printf("1-unlock: fcntl error\n"); exit(1); } printf("unlock [%d~%d]\n",start,len); } makefile
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