操作系统PV操作题整理1

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本文深入探讨了四个经典并发控制场景：餐厅顾客与清洁员的互动、订票与查票的互斥操作、家庭成员间水果放置与取用的协调，以及生产者与消费者对共享缓冲区的管理。通过具体代码实现，揭示了信号量、互斥锁等同步机制在避免死锁、饥饿等问题中的关键作用。

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1 餐厅分为等待区、用餐区、厨房。等待区中有n个椅子，顾客来了有位置则坐下，没有就离开。厨房互斥使用，进入厨房后椅子后椅子空出来供顾客坐下。用餐处有m个位置，用完厨房看用餐处是否有空位，如果有空位则顾客从厨房出来并叫清洁员A清扫，没有则坐在厨房等待。顾客到用餐处用餐后，通知清洁员B进行打扫。

#include<stdio.h>
#include<conio.h>
typedef int semaphore;

struct process
{
	
};

typedef struct
{
	int value;         //资源个数
	struct process *L;
}ss;

void P(int *n)
{
	(*n)--;   //申请一个资源
	printf("apply a resource! n=%d\n",(*n));
	if((*n)<0)printf("no resources available,block the process!\n");
}

void V(int *n)
{
	(*n)++;   //释放一个资源
	printf("release a resource! n=%d\n",(*n));
	if((*n)<=0)printf("still another process is blocked, wakeup one from the block queue.\n");
}


void Student(int *kitchen,int *seats,int *desks,int *cleaner_A,int *cleaner_B)
{
	while(1)
	{
		printf("Student process\n");
		P(seats);
		P(kitchen);  //等待厨房
		printf("enter kitchen...\n");
		V(seats);  //离开椅子
		P(desks);  //等待用餐桌
		V(cleaner_A);  //可以打扫厨房
		printf("eating...\n");
		V(cleaner_B);  //可以打扫餐桌
		getch();
	}
}

void Cleaner_A(int *cleaner_A,int *kitchen)
{
	while(1)
	{
		printf("Cleaner_A process\n");
		printf("having break...\n");
		P(cleaner_A); //等待打扫
		printf("cleaning...\n");
		V(kitchen); //离开厨房
		getch();
	}
}

void Cleaner_B(int *cleaner_B,int *desks)
{
	while(1)
	{
		printf("Cleaner_B process\n");
		printf("having break...\n");
		P(cleaner_B); //等待打扫
		printf("cleaning...");
		V(desks); //离开餐桌
		getch();
	}
}

int main()
{
	int n=4,m=3;
	semaphore seats=n,desks=m,kitchen=1,cleaner_A=0,cleaner_B=0;
	Student(&kitchen,&seats,&desks,&cleaner_A,&cleaner_B);
	Cleaner_A(&cleaner_A,&kitchen);
	Cleaner_B(&cleaner_B,&desks);
	return 0;
}

2.订票与查票，可多个查票，订票者与查票者不可同时操作且按请求顺序提供服务

#include<stdio.h>
#include<conio.h>
typedef int semaphore;

struct process
{
	
};

typedef struct
{
	int value;         //资源个数
	struct process *L;
}ss;

void P(int *n)
{
	(*n)--;   //申请一个资源
	printf("apply a resource! n=%d\n",(*n));
	if((*n)<0)printf("no resources available,block the process!\n");
}

void V(int *n)
{
	(*n)++;   //释放一个资源
	printf("release a resource! n=%d\n",(*n));
	if((*n)<=0)printf("still another process is blocked, wakeup one from the block queue.\n");
}


void Order(int *w,int *rw)
{
	while(1)
	{
		P(w);//在无查询者时可以进入
		P(rw);//互斥访问系统
		printf("Order ticket...\n");
		V(rw); //释放系统访问
		V(w);  //表示查询者可以访问
		getch();
	}
}

void Check(int *w,int *rw,int *mutex,int *count)
{
	while(1)
	{
		P(w);
		P(mutex);
		if(count==0) //当第一个查询者进入系统时
			P(rw); //阻止订票者订票
		count++;
		V(mutex);
		V(w);
		printf("checking...\n");
		P(mutex);
		count--;
		if(count==0)
			V(rw);
		V(mutex);
		getch();
	}
}

int main()
{
	int count=0;//用于记录当前的查询者数量
	semaphore mutex=1; //用于对count变量的互斥访问
	semaphore rw=1; //用于保证查询者和订票者互斥访问系统
	semaphore w=1; //用于保证查询者和订票者都不优先
	Order(&w,&rw);
	Check(&w,&rw,&mutex,&count);
	return 0;
}

3.一个果盘可以放两个水果，父亲放苹果，母亲放橘子，女儿取水果。要求只有一个人可以操作果盘，只有果盘里同时有苹果和橘子时，女儿才可以取水果，并且同时把两个水果取走。这个程序有问题会造成死锁，解决方法是采取同步机制，dad放完苹果后要释放mutex信号量，然后要等到果盘空了才能继续放，mom要等到apple信号量才能放，释放apple，释放mutex，女儿进程没有问题，所以应当再增加一个信号量来解决同步问题

#include<stdio.h>
#include<conio.h>
typedef int semaphore;

struct process
{
	
};

typedef struct
{
	int value;         //资源个数
	struct process *L;
}ss;

void P(int *n)
{
	(*n)--;   //申请一个资源
	printf("apply a resource! n=%d\n",(*n));
	if((*n)<0)printf("no resources available,block the process!\n");
}

void V(int *n)
{
	(*n)++;   //释放一个资源
	printf("release a resource! n=%d\n",(*n));
	if((*n)<=0)printf("still another process is blocked, wakeup one from the block queue.\n");
}



void dad(int *empty,int *apple,int *mutex)
{
	printf("dad process\n");
	while(1)
	{
		printf("prepare an apple...\n");
		P(empty);
		P(mutex);
		printf("put an apple...\n");
		V(apple);
		getch();
	}
}

void mom(int *empty,int *mutex,int *orange)
{
	printf("mom process\n");
	while(1)
	{
		printf("prepare an orange...\n");
		P(empty);
		P(mutex);
		printf("put an orange...\n");
		V(orange);
		getch();
	}
}

void daughter(int *apple,int *orange,int *empty,int *mutex)
{
	printf("duaghter process\n");
	while(1)
	{
		P(apple);
		P(orange);
		P(mutex);
		printf("take fruits...\n");
		V(mutex);
		V(empty);
		V(empty);
		getch();
	}
}

int main()
{
	semaphore mutex=1,apple=0,orange=0,empty=2;
	dad(&empty,&apple,&mutex);
	mom(&empty,&mutex,&orange);
	daughter(&apple,&orange,&empty,&mutex);
	return 0;
}

4.N个生产者进程和M个消费者进程共享大小为K的缓冲区，规则如下，进程之间互斥访问缓冲区，对每条放入缓冲区的数据，所有消费者必须接受一次，缓冲区满时，生产者必须阻塞，缓冲区空时，消费者必须阻塞。

#include<stdio.h>
#include<conio.h>

#define M 10
#define k 5
typedef int semaphore;

struct process
{
	
};

typedef struct
{
	int value;         //资源个数
	struct process *L;
}ss;

void P(int *n)
{
	(*n)--;   //申请一个资源
	printf("apply a resource! n=%d\n",(*n));
	if((*n)<0)printf("no resources available,block the process!\n");
}

void V(int *n)
{
	(*n)++;   //释放一个资源
	printf("release a resource! n=%d\n",(*n));
	if((*n)<=0)printf("still another process is blocked, wakeup one from the block queue.\n");
}


void producer(int *empty,int *mutex,int *full)
{
	int i;
	while(1)
	{
		for(i=1;i<M;i++)
			P(&empty[i]);
		P(mutex);
		printf("put data...\n");
		V(mutex);
		for(i=1;i<=M;i++)
			V(&full[i]);
		getch();
	}
}


void consumer(int *mutex,int *full,int *empty)
{
	int i;
	while(1)
	{
		P(&full[i]);
		P(mutex);
		printf("take out data...\n");
		V(mutex);
		V(&empty[i]);
		getch();
	}
}


int main()
{
	semaphore mutex=1;
	semaphore empty[M]={k};
	semaphore full[M]={0};
	producer(empty,&mutex,full);
	consumer(&mutex,full,empty);
	return 0;
}