实验来自《UNIX操作系统实验教程》
实验内容：控制进程间实现互斥
用lockf函数给共享同一资源的多个进程加锁、解锁，实现进程之间的互斥。
源代码
#include
#include
#include
#include
#include
#include
#include
void lock(int fd);
void unlock(int fd);
void main()
{
int fd;
pid_t pid;
char str[80];
fd=open("lock.tmp",O_RDWR|O_CREAT,0644);
if((pid=fork())==-1)
perror("fork()");
else if(pid>0){
lock(fd);
printf("I am a parent process,my pid is %d\n",getpid());
printf("Please enter a string:\n");
scanf("%s",str);
lseek(fd,0L,0);
write(fd,str,sizeof(str));
unlock(fd);
wait(NULL);
close(fd);
}
else{
sleep(1);
lock(fd);
lseek(fd,0L,0);
char str_tmp[80];
read(fd,str_tmp,sizeof(str));
unlock(fd);
printf("\nI am a child process,my pid is %d\n",getpid());
printf("the entered string from my parent process is:%s\n",str_tmp);
}
}
void lock(int fd)
{
lseek(fd,0L,0);
if(lockf(fd,F_LOCK,0L)==-1){
perror("lock()");
}
}
void unlock(int fd)
{
lseek(fd,0L,0);
if(lockf(fd,F_ULOCK,0L)==-1){
perror("unlock()");
}
}
运行结果：
[huazi@huazi ~]$ ./lockf.o
I am a parent process,my pid is 15673
Please enter a string:
mlgb
I am a child process,my pid is 15674
the entered string from my parent process is:mlgb
总结：sleep函数起了很重要的作用。因为它确保了父进程的写先于子进程的读。