使用if语句判断

#define CHAIRS 100
semaphore mutex=1;
int readers=0;

void reader()
{
do
{
	P(mutex);
	if(readers<CHAIRS)
	{
		readers++;
		填表;
		V(mutex);//mutex用于访问readers和填表
--------------------------------------------
		阅读;
--------------------------------------------
		P(mutex);
		readers--;
		撤销登记;
		V(mutex);
	}
	else
	{
		V(mutex);
	}
}while(1);
}

椅子使用信号量

semaphore mutex=1;
semaphore reader=0;
semaphore emptyseats=100;


void getin()
{
-------------------------------------------------------
emptyseats用于两个线程的同步
如果满了，只有getout后才能有读者getin
-------------------------------------------------------
	P(emptyseats);
	P(mutex);
--------------------------------------------
    mutex用于互斥访问表这个临界变量
    填表;
--------------------------------------------
	V(mutex);
	V(reader);
}

void getout()
{
-------------------------------------------------------
reader用于两个线程的同步，getin后才会有读者getout
-------------------------------------------------------
	P(reader);
	P(mutex);
--------------------------------------------
    mutex用于互斥访问表这个临界变量
    撤销登记;
--------------------------------------------
	V(mutex);
	V(emptyseats);
}