#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#include <unistd.h>
//自定义错误处理函数
void my_err(const char *err_string,int line)
{
fprintf(stderr,"line:%d ",line);
perror(err_string);
exit(1);
}
//锁的设置和释放函数
int lock_set(int fd,struct flock *lock)
{
if(fcntl(fd,F_SETLK,lock)==0)
{
if (lock->l_type==F_RDLCK)
printf("set read lock,pid:%d\n",getpid());
if(lock->l_type==F_WRLCK)
printf("set write lock ,pid:%d\n",getpid());
if (lock->l_type=F_UNLCK)
printf("release lock,pid:%d\n",getpid());
}
else
{
perror("lock operation fail\n");
return -1;
}
return 0;
}
//测试锁，只有当测试发现参数lock置顶的锁能被设置时，返回0
int lock_test(int fd,struct flock *lock)
{
if (fcntl(fd,F_GETLK,lock)==0)
{
if(lock->l_type==F_UNLCK)
{
printf("lock can be set in fd\n");
return 0;
}
else
{
if(lock->l_type==F_RDLCK)
printf("can't set lock,read lock has been set by:%d\n",lock->l_pid);
else if (lock->l_type==F_WRLCK)
printf("can't set lock,write lock has been set by:%d\n",lock->l_pid);
return -2;
}
}
else
{
perror("get incompatible locks fail");
return -1;
}
}
int main()
{
int fd;
int ret;
struct flock lock;
char read_buf[32];
char write_buf[32]="lock test";
//打开或创建文件
if((fd=open("rest.c",O_RDWR|O_CREAT|O_TRUNC, 0777))==-1)
my_err("open",__LINE__);
else
printf("create success\n");
if(write(fd,write_buf,strlen(write_buf))!=strlen(write_buf))
my_err("write",__LINE__);
else
printf("write success\n");
//初始化lock机构
memset(&lock,0,sizeof(struct flock));
lock.l_start=SEEK_SET;
lock.l_whence=0;
lock.l_len=0;
//设置读锁
lock.l_type=F_RDLCK;
if(lock_test(fd,&lock)==0)
{
lock.l_type=F_RDLCK;
lock_set(fd,&lock);
}
//读数据
lseek(fd,0,SEEK_SET);
if((ret=read(fd,read_buf,10))<0)
my_err("read",__LINE__);
read_buf[ret]='\0';
printf("%s\n",read_buf);
//等待任意按键
getchar();
//设置写锁
lock.l_type=F_WRLCK;
if(lock_test(fd,&lock)==0)
{
lock.l_type=F_WRLCK;
lock_set(fd,&lock);
}
//释放锁
lock.l_type=F_UNLCK;
lock_set(fd,&lock);
close(fd);
return 0;
}
