/*lock_set函數(shù)*/
void lock_set(int fd, int type)
{
struct flock lock;
lock.l_whence = SEEK_SET;//賦值lock結(jié)構(gòu)體
lock.l_start = 0;
lock.l_len =0;
while(1){
lock.l_type = type;
/*根據(jù)不同的type值給文件上鎖或解鎖*/
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;
}
/*判斷文件是否可以上鎖*/
fcntl(fd, F_GETLK,&lock);
/*判斷文件不能上鎖的原因*/
if(lock.l_type != F_UNLCK){
/*/該文件已有寫入鎖*/
if( lock.l_type == F_RDLCK )
printf("read lock already set by %d\n",lock.l_pid);
/*該文件已有讀取鎖*/
else if( lock.l_type == F_WRLCK )
printf("write lock already set by %d\n",lock.l_pid);
getchar();
}
}
}

/*fcntl_write.c測試文件寫入鎖主函數(shù)部分*/
#include <unistd.h>
#include <sys/file.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
int fd;
/*首先打開文件*/
fd=open("hello",O_RDWR | O_CREAT, 0666);
if(fd < 0){
perror("open");
exit(1);
}
/*給文件上寫入鎖*/
lock_set(fd, F_WRLCK);
getchar();
/*給文件接鎖*/
lock_set(fd, F_UNLCK);
getchar();
close(fd);
exit(0);
}

[root@localhost file]# ./fcntl_write
write lock set by 4994
release lock by 4994

[root@localhost file]# ./fcntl_write
write lock already set by 4994
write lock set by 4997
release lock by 4997

/*fcntl_read.c測試文件讀取鎖主函數(shù)部分*/
#include <unistd.h>
#include <sys/file.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
int fd;
fd=open("hello",O_RDWR | O_CREAT, 0666);
if(fd < 0){
perror("open");
exit(1);
}
/*給文件上讀取鎖*/
lock_set(fd, F_RDLCK);
getchar();
/*給文件接鎖*/
lock_set(fd, F_UNLCK);
getchar();
close(fd);
exit(0);
}

[root@localhost file]# ./fcntl2
read lock set by 5009
release lock by 5009

[root@localhost file]# ./fcntl2
read lock set by 5010
release lock by 5010