c++ - 互斥和信号量

Question

我正在编写一个模拟男女通用浴室的程序(用于家庭作业)。一次只允许 4 人进入，如果异性已经在使用洗手间，则男性和女性不能进入。我的问题是最多允许 4 人进入浴室。从输出中可以看出，一次只有 1 个人进入洗手间。这是我的代码:

const int Delayx = 60;
int i;
int restroom = 0;
int Menwaiting = 0;
int Womenwaiting = 0;
semaphore max_capacity;
semaphore woman;
semaphore man;
semaphore mutex;
semaphore restroomcount;
void Delay(void)
{
    int DelayTime;
    DelayTime = random(Delayx);
    for (i = 0; i<DelayTime; i++);
}

void Woman(void)
{
//  for(;;){
    Womenwaiting++;
    //wait(mutex);
    wait(woman);
    wait(max_capacity);
        //wait(woman);
        wait(mutex);
        wait(restroomcount);
        cout << "A Woman has entered Restroom"<<endl;
        cout << "People in the Restroom:" << restroom++ <<endl <<endl;
        signal(restroomcount);
        Womenwaiting--;
        Delay();
        wait(restroomcount);
        cout << "A woman has exited Restroom"<<endl;
        cout << "People in the Restroom:" << restroom-- <<endl<<endl;
        signal(restroomcount);
        signal(mutex);
        signal(max_capacity);
        if(Menwaiting > Womenwaiting){
              signal(man);
                  }
              else{
            signal(woman);
        }
        //signal(max_capacity);
    //signal(man);
//  }
}
void Man(void)
{
//  for(;;){
    Menwaiting++;
    //wait(mutex);
    wait(man);
    wait(max_capacity);
    //wait(man);
        wait(mutex);
        wait(restroomcount);
        cout <<"A Man has entered the Restroom"<<endl;
        cout <<"People in the Restroom:" << restroom++ <<endl<<endl;
        signal(restroomcount);
        Menwaiting--;
        //signal(mutex);
        Delay();
        //wait(mutex);
        wait(restroomcount);
        cout << "A man has exited the Restroom"<<endl;
        cout <<"People in the Restroom:" << restroom-- <<endl<<endl;
        signal(restroomcount);
        signal(mutex);
        signal(max_capacity);
        if(Womenwaiting > Menwaiting){
            signal(woman);
            }
        else{
            signal(man);
            }
        //signal(max_capacity);
        //signal(woman);
//}
}
void main()
{
    initialsem(woman,1);
    initialsem(man,1);
    initialsem(max_capacity,4);
    initialsem(mutex,1);
    initialsem(restroomcount,1);
    cobegin
    {
        Woman(); Woman(); Woman(); Woman(); Woman(); Man();  Man(); Man(); Man(); Man();
    }

}

这会生成以下输出:

A Man has entered the Restroom
People in the Restroom:1

A man has exited the Restroom
People in the Restroom:0

A Man has entered the Restroom
People in the Restroom:1

A man has exited the Restroom
People in the Restroom:0

A Woman has entered Restroom
People in the Restroom:1

A woman has exited Restroom
People in the Restroom:0

A Woman has entered Restroom
People in the Restroom:1

A woman has exited Restroom
People in the Restroom:0

以此类推，直到永远。

Answer 1

我认为你的信号量太多了。你的男人/女人信号灯一次只针对 1 个人。考虑使用一些受互斥锁保护的状态变量(浴室的当前性别、浴室中的人数)而不是这么多不同的信号量。

您是否保持排队顺序，或者人们是否可以根据当前洗手间性别跳过？例如，如果你有 woman,woman,woman,man,woman，第 4 个女人是否允许跳过男人进入洗手间，或者让 3 个女人退出，然后男人进入/退出，然后女人可以进入？这是一个比允许跳过更容易的问题。