信号量与并发编程

Question

对于家庭作业，我需要规划以下场景。这将使用使用BACI (即C-)的信号量来完成。

有2间男女同床共枕的洗手间，每个可容纳4人。因为它是男女同性别的，只有同性别的人可以同时在洗手间，而FIFO并不重要。我有一个基本的“算法”在我的头脑中处理4个男人和4个女人在一个洗手间。但我不知道该怎么编码。任何帮助都将不胜感激。这是我所拥有的。

Woman:

Check to see if there are any men in the restroom. If so "wait".
If no men check to see if there are 4 people. If so "wait".
If no men and not 4 use restroom. When leaving signal there is a vacancy.
If last woman signal the men if they are waiting if not signal the woman.


Man:

check to see if there are any woman in the restroom. if so "wait"
If no woman check to see if there are 4 people. If so "wait".
If no woman and not 4 use restroom. when leaving signal there is a vacancy.
if last man signal the women if they are waiting if not signal the men.

提供了这些额外的指示

• 使用随机的FOR循环来模拟时间在适当的地方的流逝。通过使用延迟函数可以很容易地做到这一点： 空延迟( void ) { int i；int DelayTime；DelayTime =随机(延迟)；for (i = 0；i< DelayTime；i++)：}
• 其中，const延迟=从10到100之间的某个数。
• 很好地打印和格式化输出，并以这样的方式打印消息，通过读取输出，可以跟踪执行顺序。
• 将进程设置为永久循环，并使用控制C(或控制中断)来停止程序。

Answer 1

因为您想知道how to code your algorithm for 1 restroom，所以我已经在C中这样做了。将它转换为C是一个相当简单的任务--因为所有的信号量结构看起来都非常相似。

根据我对你的答案的理解，

C: sem_wait()  C--: wait()
   sem_post()       signal()
   sem_t            semaphore()
   sem_init()       initialsem() 

请记住，如前所述，我已经为1--仅限于卫生间解决了这个问题。既然这是家庭作业，我希望你自己把它扩展到2-洗手间表单。

从读者-作家问题到我们的"Unisex洗手间“问题，我们使用了以下全局变量：

int mcount,wcount; // count of number of men/women in restroom
sem_t x,y,z;       // semaphores for updating mcount & wcount values safely
sem_t wsem,msem;   // semaphores to block other genders' entry  
sem_t cap;         // capacity of the restroom

将这些信号量和计数器合并到man线程函数中，

void *man(void *param)
{           
    sem_wait(&z);                
        sem_wait(&msem);        
            sem_wait(&x);
                mcount++;
                if(mcount==1)   
                { sem_wait(&wsem); } // first man in, make women wait
            sem_post(&x);
        sem_post(&msem);
    sem_post(&z);

    sem_wait(&cap);  //wait here, if over capacity

    printf("\t\tman in!\n");
    delay();
    printf("\t\t\tman out!\n");

    sem_post(&cap);  //one man has left, increase capacity

    sem_wait(&x);
        mcount--;
        if(mcount==0)
        {sem_post(&wsem);}  // no man left, signal women 
    sem_post(&x);
}

类似地，妇女线程函数将mcount替换为wcount，msem替换为wsem，x替换为y。只有z保持在man函数中，因此man和woman线程都在同一个通用信号量上排队。(正因为如此，代码始终具有类似于fairness/non-starvation)的FIFO行为，从而确保了。

完整的代码如下(要编译，使用gcc filename -lpthread)

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>

int mcount,wcount;
sem_t x,y,z,wsem,msem,cap;

void delay(void)
{
    int i;
    int delaytime;
    delaytime = random();
    for (i = 0; i<delaytime; i++);
}

void *woman(void *param)
{
    sem_wait(&z);
        sem_wait(&wsem);
            sem_wait(&y);
                wcount++;
                if(wcount==1)
                { sem_wait(&msem); }
            sem_post(&y);
        sem_post(&wsem);
    sem_post(&z);

    sem_wait(&cap);

    printf("woman in!\n");
    delay();
    printf("\twoman out!\n");

    sem_post(&cap);     

    sem_wait(&y);
        wcount--;
        if(wcount==0)
        { sem_post(&msem); }
    sem_post(&y);
}

void *man(void *param)
{           
    sem_wait(&z);
        sem_wait(&msem);
            sem_wait(&x);
                mcount++;
                if(mcount==1)
                { sem_wait(&wsem); }
            sem_post(&x);
        sem_post(&msem);
    sem_post(&z);

    sem_wait(&cap);

    printf("\t\tman in!\n");
    delay();
    printf("\t\t\tman out!\n");

    sem_post(&cap);

    sem_wait(&x);
        mcount--;
        if(mcount==0)
        {sem_post(&wsem);}
    sem_post(&x);
}

int main(void)
{
    int i;
    srandom(60);

        mcount = 0;
        wcount = 0;
        sem_init(&x,0,1);  // for sem_init, initial value is 3rd argument
        sem_init(&y,0,1);
        sem_init(&z,0,1);
        sem_init(&wsem,0,1);
        sem_init(&msem,0,1);
        sem_init(&cap,0,4);  // eg. cap initialized to 4

        pthread_t *tid;
        tid = malloc(80*sizeof(pthread_t));

    // You can use your cobegin statement here, instead of pthread_create()     
    // I have forgone the use of pthread barriers although I suppose they would nicely imitate the functionality of cobegin. 
    // This is merely to retain simplicity.

    for(i=0;i<10;i++)
    {
        pthread_create(&tid[i],NULL,woman,NULL);
    }
    for(i=10;i<20;i++)
    {     
            pthread_create(&tid[i],NULL,man,NULL);
    }
    for(i=0;i<20;i++)
    {     
            pthread_join(tid[i],NULL);
    }

    return(0);
}

在转换为2-休息室表单时，请注意您需要复制哪些信号量和计数器变量，以满足所有条件。信号传递快乐！

Answer 2

这是我所拥有的。这允许一个人一次在厕所没有死锁或饥饿。我需要帮助，如何使它，以便4人可以在厕所一次。

const int Delayx = 60;
int i;
semaphore max_capacity;
semaphore woman;
semaphore man;
semaphore mutex;

void Delay(void)
{
    int DelayTime;
    DelayTime = random(Delayx);
    for (i = 0; i<DelayTime; i++);
}

void Woman(void)
{
    wait(woman);
    wait(max_capacity);
    wait(mutex);
    cout << "A Woman has entered Restroom"<<endl;
    Delay();
    cout << "A woman has exited Restroom"<<endl;
    signal(mutex);
    signal(max_capacity);
    signal(man);
}

void Man(void)
{
    wait(man);
    wait(max_capacity);
    wait(mutex);
    cout <<"A Man has entered the Restroom"<<endl;
    Delay();
    cout << "A man has exited the Restroom"<<endl;
    signal(mutex);
    signal(max_capacity);
    signal(woman);
}

void main()
{
    initialsem(woman,1);
    initialsem(man,1);
    initialsem(max_capacity,4);
    initialsem(mutex,1);
    cobegin
    {
        Woman(); Woman(); Woman(); Woman(); Woman(); Woman(); Woman(); Woman(); Man();  Man(); Man(); Man(); Man(); Man(); Man(); Man();
    }
}

Answer 3

4间洗手间的杆菌码：

 const int Delayx = 60;
   int i;
   int Mcount,Wcount;
   binarysem x,y,z,Wsem,Msem;
   semaphore cap;
   void Delay(void)
   {
    int DelayTime;
    DelayTime = random(Delayx);
    for (i = 0; i<DelayTime; i++);
     }

 void Woman(void)
   {
     wait(z);
     wait(Wsem);
     wait(y);
     Wcount++;
     if(Wcount==1)
       { wait(Msem);  }
       signal(y);
       signal(Wsem);
       signal(z);

       wait(cap);
       cout << "A Woman has entered Restroom"<<endl;
       Delay();
       cout << "A Woman has exited Restroom"<<endl;

       signal(cap);
       wait(y);
       Wcount--;
       if(Wcount==0)
         {signal(Msem);}

        signal(y);
        }

 void Man(void)
  {
     wait(z);
     wait(Msem);
     wait(x);
     Mcount++;
     if(Mcount==1)
       { wait(Wsem);  }
       signal(x);
       signal(Msem);
       signal(z);

       wait(cap);
       cout << "A Man has entered Restroom"<<endl;
       Delay();
       cout << "A Man has exited Restroom"<<endl;

       signal(cap);
       wait(x);
       Mcount--;
       if(Mcount==0)
         {signal(Wsem);}

        signal(x);
        }


void main()
{
Mcount=0;
Wcount=0;
initialsem(x,1);
initialsem(y,1);
initialsem(z,1);
initialsem(Wsem,1);
initialsem(Msem,1);
initialsem(cap,4);
cobegin
{
    Woman(); Woman(); Woman();
    Woman(); Woman(); Woman(); 
    Woman();
    Woman(); Man();  Man();
    Man(); Man(); Man(); Man();
    Man(); Man();
}
      }