文件加锁
1. 例子
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
void lock_set(int fd, int type) {
struct flock lock;
lock.l_whence = SEEK_SET;
lock.l_start = 0;
lock.l_len = 0;
while (1) {
lock.l_type = type;
if ((fcntl(fd, F_SETLK, &lock)) == 0) {
if (lock.l_type == F_RDLCK)
printf("read lock set by %d\n", getpid());
else if(lock.l_type == F_WRLCK)
printf("write lock set by %d\n", getpid());
else if (lock.l_type == F_UNLCK)
printf("release lock by %d\n", getpid());
return;
}
//检查文件是否可以上锁
fcntl(fd, F_GETLK, &lock);
//判断不能上锁的原因
if (lock.l_type != F_UNLCK) {
if (lock.l_type == F_RDLCK)
printf("read lock has been already set by %d\n", getpid());
else if (lock.l_type == F_WRLCK)
printf("write lock has been already set by %d\n", getpid());
getchar();
}
}
}
int main() {
int fd;
fd = open("data", O_RDWR | O_CREAT, 0666);
if (fd < 0) {
perror("open failed");
return -1;
}
lock_set(fd, F_WRLCK);
getchar();
lock_set(fd, F_UNLCK);
getchar();
close(fd);
return 0;
}