请教一个linux文件锁的问题
#include<stdio.h>
#include<sys/stat.h>
#include<sys/types.h>
#include<fcntl.h>
#include<unistd.h>
#include<errno.h>
#include<string.h>
my_error(char *p,int n){
perror(p);
printf("line=%d",n);
}
int main()
{ int fd;
char a[50]="abcdef";
int n;
char b[50];
struct flock lock;
fd=open("example.c",O_RDWR|O_CREAT,0666);
if(fd==-1){
my_error("open",__LINE__);
// exit(1);
}
else
printf("text is ok\n");
if( write(fd,a,strlen(a)+1)==strlen(a)+1)
my_error("write",__LINE__);
printf("写入成功\n");
n=lseek(fd,0,SEEK_END);
if(n==-1)
my_error("lseek",__LINE__);
else
printf("n=%d\n",n);
n=lseek(fd,0,SEEK_SET);
printf("n=%d\n",n);
read(fd,b,strlen(a)+1);
printf("%s\n",b);
memset(&lock,0,sizeof(struct flock ));
lock.l_whence=SEEK_SET;
lock.l_start=0;
lock.l_len=0;
lock.l_type=F_WRLCK;
if( fcntl(fd,F_SETLK,&lock)==0)
printf(" lock is ok\n");
else
printf("error");
if(fcntl(fd,F_GETLK,&lock)==0)
printf("file %d is lock",getpid());
if(lock.l_type==F_RDLCK)
printf(" RDLCK");
else if(lock.l_type==F_WRLCK)
printf(" WRLCK");
else if(lock.l_type==F_UNLCK)
printf(" UNLCK");
getchar();
close(fd);
return 0;
}
想给文件加锁 为什么最后显示 UNLCK
[解决办法]
结构体lock的定义呢？。。。求源码
[解决办法]
貌似没有办法来获取文件上当前有哪些锁
F_GETLK 的准确语义是获取会阻止我的加锁操作的第一个锁
If no lock is found that would prevent this lock from being created, the structure is left unchanged, except for lock type (l_type) which is set to F_UNLCK.
The definition of the F_GETLK command states that the information returned applies to an existing lock that would prevent us from creating our own lock. Since the F_SETLK and F_SETLKW commands always replace a process's existing lock if it exists, we can never block on our own lock; thus, the F_GETLK command will never report our own lock.
