操作系统的题目,关于用户态 核心态

关中断指令只能在内核模式下运行.
生产消费者 Semphore mutex=1,empty=n,full=0;
Item buffer[n];
int in=out=0;
Producers()
{while(1)
{produce an item in nextp;
wait empty;
wait mutex;
buffer[in]=nextp;
in=(in+1)mod n;
signal mutex;
signal full;}}
Consumers() {
while(1)
{ wait full;
wait mutex;
nextc=buffer[out];
out=(out+1)mod n;
signal mutex;
signal empty;
consume the item in nextc;}} //n为缓冲区大小