生产者，消费者问题

互斥锁实现：

“生产者/消费者”问题描述：

有一个有限缓冲区和两个线程：生产者和消费者。他们分别把产品放入缓冲区和从缓冲区中拿走产品。当一个生产者在缓冲区满时必须等待，当一个消费者在缓冲区空时也必须等待。

1.      单锁模型

#include”stdio.h”
#include”pthread.h”

int buffer[10];
int top = 0;
int itime = 0;
int itime2 = 0;

pthread_t thread[2];
pthread_mutex_t mut;

void producer()
{
    while(1)
    {
        if(itime == 10) return;
        pthread_mutex_lock(&mut);
        if(top == 10)
        {
            printf(”buffer is full…producer is waiting…\n”);
            pthread_mutex_unlock(&mut);
            continue;
        }
        printf(”pruducter set the %d\n”, itime);
        top++;
        itime++;
        pthread_mutex_unlock(&mut);
    }
}


void consumer()
{
    while(1)
    {
        if(itime2 == 10) return;
        pthread_mutex_lock(&mut);
        if(top == 0)
        {
            printf(”buffer is empty…consumer is waiting…\n”);
            pthread_mutex_unlock(&mut);
            continue;
        }
        printf(”consumer get the %d\n”, itime2);
        top–;
        itime2++;
        pthread_mutex_unlock(&mut);
    }
}

int main()
{
    pthread_create(&thread[0], NULL, (void*)(&producer), NULL);
    pthread_create(&thread[1], NULL, (void*)(&consumer), NULL);

    sleep(1);
    return 0;
}

#include"stdio.h"

#include"pthread.h" int buffer[10]; int top = 0; int itime = 0; int itime2 = 0; pthread_t thread[2]; pthread_mutex_t mut; void producer() { while(1) { if(itime == 10) return; pthread_mutex_lock(&mut); if(top == 10) { printf("buffer is full...producer is waiting...\n"); pthread_mutex_unlock(&mut); continue; } printf("pruducter set the %d\n", itime); top++; itime++; pthread_mutex_unlock(&mut); } } void consumer() { while(1) { if(itime2 == 10) return; pthread_mutex_lock(&mut); if(top == 0) { printf("buffer is empty...consumer is waiting...\n"); pthread_mutex_unlock(&mut); continue; } printf("consumer get the %d\n", itime2); top--; itime2++; pthread_mutex_unlock(&mut); } } int main() { pthread_create(&thread[0], NULL, (void*)(&producer), NULL); pthread_create(&thread[1], NULL, (void*)(&consumer), NULL); sleep(1); return 0; }

运行结果

buffer is empty…consumer is waiting…
buffer is empty…consumer is waiting…
buffer is empty…consumer is waiting…
pruducter set the 0
pruducter set the 1
pruducter set the 2
pruducter set the 3
pruducter set the 4
pruducter set the 5
pruducter set the 6
pruducter set the 7
pruducter set the 8
pruducter set the 9
consumer get the 0
consumer get the 1
consumer get the 2
consumer get the 3
consumer get the 4
consumer get the 5
consumer get the 6
consumer get the 7
consumer get the 8
consumer get the 9

buffer is empty...consumer is waiting...
buffer is empty...consumer is waiting...
buffer is empty...consumer is waiting...
pruducter set the 0
pruducter set the 1
pruducter set the 2
pruducter set the 3
pruducter set the 4
pruducter set the 5
pruducter set the 6
pruducter set the 7
pruducter set the 8
pruducter set the 9
consumer get the 0
consumer get the 1
consumer get the 2
consumer get the 3
consumer get the 4
consumer get the 5
consumer get the 6
consumer get the 7
consumer get the 8
consumer get the 9

分析

容易出现极端状况，一开始一直是consumer加锁，producer无法提供；不久后producer终于得到加锁，存入了10个货物，而后consumer取得10个货物。

 2. 两个互斥锁

#include”stdio.h”
#include”pthread.h”

int buffer[10];
int top = 0;
int itime = 0;
int itime2 = 0;

pthread_t thread[2];
pthread_mutex_t mut;
pthread_mutex_t mut2;

void producer()
{
    while(1)
    {
        if(itime == 10) return;
        pthread_mutex_lock(&mut);
        if(top == 10)
        {
            printf(”buffer is full…producer is waiting…\n”);
            pthread_mutex_unlock(&mut2);
            continue;
        }
        printf(”pruducter set the %d\n”, itime);
        top++;
        itime++;
        pthread_mutex_unlock(&mut2);
    }
}


void consumer()
{
    while(1)
    {
        if(itime2 == 10) return;
        pthread_mutex_lock(&mut2);
        if(top == 0)
        {
            printf(”buffer is empty…consumer is waiting…\n”);
            pthread_mutex_unlock(&mut);
            continue;
        }
        printf(”consumer get the %d\n”, itime2);
        top–;
        itime2++;
        pthread_mutex_unlock(&mut);
    }
}

int main()
{
    pthread_create(&thread[0], NULL, (void*)(&producer), NULL);
    pthread_create(&thread[1], NULL, (void*)(&consumer), NULL);

    sleep(1);
    return 0;
}

#include"stdio.h"

#include"pthread.h" int buffer[10]; int top = 0; int itime = 0; int itime2 = 0; pthread_t thread[2]; pthread_mutex_t mut; pthread_mutex_t mut2; void producer() { while(1) { if(itime == 10) return; pthread_mutex_lock(&mut); if(top == 10) { printf("buffer is full...producer is waiting...\n"); pthread_mutex_unlock(&mut2); continue; } printf("pruducter set the %d\n", itime); top++; itime++; pthread_mutex_unlock(&mut2); } } void consumer() { while(1) { if(itime2 == 10) return; pthread_mutex_lock(&mut2); if(top == 0) { printf("buffer is empty...consumer is waiting...\n"); pthread_mutex_unlock(&mut); continue; } printf("consumer get the %d\n", itime2); top--; itime2++; pthread_mutex_unlock(&mut); } } int main() { pthread_create(&thread[0], NULL, (void*)(&producer), NULL); pthread_create(&thread[1], NULL, (void*)(&consumer), NULL); sleep(1); return 0; }
运行结果

buffer is empty…consumer is waiting…
pruducter set the 0
consumer get the 0
pruducter set the 1
consumer get the 1
pruducter set the 2
consumer get the 2
pruducter set the 3
consumer get the 3
pruducter set the 4
consumer get the 4
pruducter set the 5
consumer get the 5
pruducter set the 6
consumer get the 6
pruducter set the 7
consumer get the 7
pruducter set the 8
consumer get the 8
pruducter set the 9
consumer get the 9

buffer is empty...consumer is waiting...
pruducter set the 0
consumer get the 0
pruducter set the 1
consumer get the 1
pruducter set the 2
consumer get the 2
pruducter set the 3
consumer get the 3
pruducter set the 4
consumer get the 4
pruducter set the 5
consumer get the 5
pruducter set the 6
consumer get the 6
pruducter set the 7
consumer get the 7
pruducter set the 8
consumer get the 8
pruducter set the 9
consumer get the 9

很完美对不对？生产者生产一个就把自己锁起来，消费者消费一个后解锁生产者，把自己锁起来，生产者继续生产，循环反复。互斥锁的确能很好的实现进程/线程之间的同步问题，但是它是通过锁机制来实现的，就是仅仅通过加锁和解锁实现同步，效率比较低。

3. 利用条件变量

#include”stdio.h”
#include”pthread.h”

int buffer[10];
int top = 0;
int itime = 0;
int itime2 = 0;

pthread_t thread[2];
pthread_mutex_t mut;
pthread_cond_t con, con2;

void producer()
{
    while(1)
    {
        if(itime == 10) return;
        pthread_mutex_lock(&mut);
        if(top == 10)
        {
            printf(”buffer is full…producer is waiting…\n”);
            pthread_cond_wait(&con, &mut);
        }
        printf(”pruducter set the %d\n”, itime);
        top++;
        itime++;
        pthread_cond_signal(&con2);
        pthread_mutex_unlock(&mut);
        sleep(1);
    }
}


void consumer()
{
    while(1)
    {
        if(itime2 == 10) return;
        pthread_mutex_lock(&mut);
        if(top == 0)
        {
            printf(”buffer is empty…consumer is waiting…\n”);
            pthread_cond_wait(&con2, &mut);
        }
        printf(”consumer get the %d\n”, itime2);
        top–;
        itime2++;
        pthread_cond_signal(&con);
        pthread_mutex_unlock(&mut);
        sleep(1);
    }
}

int main()
{
    pthread_create(&thread[0], NULL, (void*)(&producer), NULL);
    pthread_create(&thread[1], NULL, (void*)(&consumer), NULL);

    sleep(10);
    return 0;
}

#include"stdio.h"

#include"pthread.h" int buffer[10]; int top = 0; int itime = 0; int itime2 = 0; pthread_t thread[2]; pthread_mutex_t mut; pthread_cond_t con, con2; void producer() { while(1) { if(itime == 10) return; pthread_mutex_lock(&mut); if(top == 10) { printf("buffer is full...producer is waiting...\n"); pthread_cond_wait(&con, &mut); } printf("pruducter set the %d\n", itime); top++; itime++; pthread_cond_signal(&con2); pthread_mutex_unlock(&mut); sleep(1); } } void consumer() { while(1) { if(itime2 == 10) return; pthread_mutex_lock(&mut); if(top == 0) { printf("buffer is empty...consumer is waiting...\n"); pthread_cond_wait(&con2, &mut); } printf("consumer get the %d\n", itime2); top--; itime2++; pthread_cond_signal(&con); pthread_mutex_unlock(&mut); sleep(1); } } int main() { pthread_create(&thread[0], NULL, (void*)(&producer), NULL); pthread_create(&thread[1], NULL, (void*)(&consumer), NULL); sleep(10); return 0; }

运行结果

buffer is empty…consumer is waiting…
pruducter set the 0
consumer get the 0
buffer is empty…consumer is waiting…
pruducter set the 1
consumer get the 1
buffer is empty…consumer is waiting…
pruducter set the 2
consumer get the 2
buffer is empty…consumer is waiting…
pruducter set the 3
consumer get the 3
pruducter set the 4
consumer get the 4
pruducter set the 5
consumer get the 5
pruducter set the 6
consumer get the 6
pruducter set the 7
consumer get the 7
pruducter set the 8
consumer get the 8
pruducter set the 9
consumer get the 9

buffer is empty...consumer is waiting...
pruducter set the 0
consumer get the 0
buffer is empty...consumer is waiting...
pruducter set the 1
consumer get the 1
buffer is empty...consumer is waiting...
pruducter set the 2
consumer get the 2
buffer is empty...consumer is waiting...
pruducter set the 3
consumer get the 3
pruducter set the 4
consumer get the 4
pruducter set the 5
consumer get the 5
pruducter set the 6
consumer get the 6
pruducter set the 7
consumer get the 7
pruducter set the 8
consumer get the 8
pruducter set the 9
consumer get the 9

结果还算比较正常，理解一下变量的使用。消费者发现缓冲区没有东西，通过条件变量把自己锁住；生产者生产并激活消费者；消费者从缓冲区消费；当生产者发现缓冲区满的时候，通过条件变量把自己锁住，消费者消费并重新激活生产者。如此。

信号量实现

 文章出自： http://page.renren.com/600235506/note/492983524

学习了信号量以及共享内存后，我们就可以实现进程的同步与互斥了。说到这里，最经典的例子莫过于生产者和消费者模型。下面就和大家一起分析，如何一步步实现这个经典模型。

下面程序，实现的是多个生产者和多个消费者对N个缓冲区（N个货架）进行访问的例子。现在先想想我们以前的伪代码是怎么写的？是不是这样：

//生产者：

while(1)
{
    p(semid,1);
    sleep(3);
    p(semid,0);
    //producer is producing a product
    goods=rand()%10;
    shmaddr[indexaddr[0]]=goods;
    printf(”producer:%d produces a product[%d]:%d\n”,getpid(),indexaddr[0],goods);
    indexaddr[0]=(indexaddr[0]+1)%10;
    v(semid,0);
    sleep(3);
    v(semid,2);
}

  while(1)
    {
        p(semid,1);
        sleep(3);
        p(semid,0);
        //producer is producing a product
        goods=rand()%10;
        shmaddr[indexaddr[0]]=goods;
        printf("producer:%d produces a product[%d]:%d\n",getpid(),indexaddr[0],goods);
        indexaddr[0]=(indexaddr[0]+1)%10;
        v(semid,0);
        sleep(3);
        v(semid,2);
    }

//消费者：

while(1)
{
    p(semid,2);
    sleep(1);
    p(semid,0);
    //consumer is consuming a product
    goods=shmaddr[indexaddr[1]];
    printf(”consumer:%d consumes a product[%d]:%d\n”,getpid(),indexaddr[1],goods);
    indexaddr[1]=(indexaddr[1]+1)%num;
    v(semid,0);
    sleep(1);
    v(semid,1);
}

   while(1)
    {
        p(semid,2);
        sleep(1);
        p(semid,0);
        //consumer is consuming a product
        goods=shmaddr[indexaddr[1]];
        printf("consumer:%d consumes a product[%d]:%d\n",getpid(),indexaddr[1],goods);
        indexaddr[1]=(indexaddr[1]+1)%num;
        v(semid,0);
        sleep(1);
        v(semid,1);
    }

 

可能上面的代码你有些眼熟，又有些困惑，因为它和课本上的代码不完全一样，其实上面的代码就是伪代码的linuxC语言具体实现。我们从上面的代码中慢慢寻找伪代码的踪迹：p(semid,0)和v(semid,0)的作用是让进程互斥访问临界区。临界区中包含的数据indexaddr[0]，indexaddr[1]，以及shmaddr数组分别对应伪代码中的in，out，buffer。p(semid,1)和v(semid,2)以及p(semid,2)和v(semid,1)实现的是同步作用。

并且，在生产者中，生产者生产了一个货物（goods=rand()%10;），然后将这个货物放上货架(shmaddr[indexaddr[0]]=goods;)。在消费者中，消费和从货架上取下货物（goods=shmaddr[indexaddr[1]];）。

好了，现在再看一边上面的代码，我想你的思路就清晰了。

了解了核心代码，并不能算就完成了生产者和消费者模型，因为生产者和消费者核心代码前还得做一些些准备工作，具体要准备些什么，我们具体来分析。

首先申请一块共享内存，这块共享内存用于存放生产者所生产的货物。同时我们可以看到这块共享内存大小为10字节。这里需要注意，每个生产着或消费者运行后，都要去试着分配这样的一块共享内存。如果在当前进程运行前已经有某个进程已经创建了这块共享内存，那么这个进程就不再创建（此时createshm会返回-1并且错误代码为EEXIST），只是打开这块共享内存。创建后，再将这块共享内存添加到当前进程的地址空间。

num=10;
//create a shared memory as goods buffer
if((shmid_goods=createshm(“.”,’s’,num))==-1)
{
    if(errno==EEXIST)
    {
        if((shmid_goods=openshm(“.”,’s’))==-1)
        {
            exit(1);
        }
    }
    else
    {
        perror(”create shared memory failed\n”);
            exit(1);
    }
}
//attach the shared memory to the current process
if((shmaddr=shmat(shmid_goods,(char*)0,0))==(char*)-1)
{
    perror(”attach shared memory error\n”);
    exit(1);
}

 num=10;
    //create a shared memory as goods buffer
    if((shmid_goods=createshm(".",'s',num))==-1)
    {
        if(errno==EEXIST)
        {
            if((shmid_goods=openshm(".",'s'))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror("create shared memory failed\n");
                exit(1);
        }
    }
    //attach the shared memory to the current process
    if((shmaddr=shmat(shmid_goods,(char*)0,0))==(char*)-1)
    {
        perror("attach shared memory error\n");
        exit(1);
    }

 

接下来还要再申请一块共享内存，用于存放两个整形变量in和out（其实就是申请一个含有2个整形变量的数组而已）。他们记录的是生产和消费货物时“货架”的索引。与上面情况相同，如果已经有其他进程创建了此块共享内存，那么当前进程只是打开它而已。

注意这里对两个整形变量的初始化时的值均为0。

//create a shared memory as index
if((shmid_index=createshm(“.”,‘z’,2))==-1)
{
    if(errno==EEXIST)
    {
        if((shmid_index=openshm(“.”,‘z’))==-1)
        {
            exit(1);
        }
    }
    else
    {
        perror(”create shared memory failed\n”);
            exit(1);
    }
}
else
{
    is_noexist=1;
}
//attach the shared memory to the current process
if((indexaddr=shmat(shmid_index,(int*)0,0))==(int*)-1)
{
    perror(”attach shared memory error\n”);
    exit(1);
}
if(is_noexist)
{
    indexaddr[0]=0;
    indexaddr[1]=0;
}

  //create a shared memory as index
    if((shmid_index=createshm(".",'z',2))==-1)
    {
        if(errno==EEXIST)
        {
            if((shmid_index=openshm(".",'z'))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror("create shared memory failed\n");
                exit(1);
        }
    }
    else
    {
        is_noexist=1;
    }
    //attach the shared memory to the current process
    if((indexaddr=shmat(shmid_index,(int*)0,0))==(int*)-1)
    {
        perror("attach shared memory error\n");
        exit(1);
    }
    if(is_noexist)
    {
        indexaddr[0]=0;
        indexaddr[1]=0;
    }

 

接下来就是创建一个信号量集，这个信号量集中包含三个信号量。第一个信号量实现的互斥作用，即进程对临界区的互斥访问。剩下两个均实现的是同步作用，协调生产者和消费者的合理运行，即货架上没有空位时候生产者不再生产，货架上无商品时消费者不再消费。

注意下面对每个信号量的赋值情况。互斥信号量当然初值为1。而同步信号量两者之和不能大于num的值。

//create a semaphore set including 3 semaphores
if((semid=createsem(“.”,‘t’,3,0))==-1)
{
    if(errno==EEXIST)
    {
        if((semid=opensem(“.”,‘t’))==-1)
        {
            exit(1);
        }
    }
    else
    {
        perror(”semget error:”);
        exit(1);
    }
}
else
{
    union semun arg;
        //seting value for mutex semaphore
            arg.val=1;
            if(semctl(semid,0,SETVAL,arg)==-1)
            {
        perror(”setting semaphore value failed\n”);
            return -1;
            }
            //set value for synchronous semaphore
        arg.val=num;
            //the num means that the producer can continue to produce num products
            if(semctl(semid,1,SETVAL,arg)==-1)
            {
        perror(”setting semaphore value failed\n”);
            return -1;
            }
            //the last semaphore’s value is default
            //the default value ‘0’ means that the consumer is not use any product now
   }

   //create a semaphore set including 3 semaphores
    if((semid=createsem(".",'t',3,0))==-1)
    {
        if(errno==EEXIST)
        {
            if((semid=opensem(".",'t'))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror("semget error:");
            exit(1);
        }
    }
    else
    {
        union semun arg;
            //seting value for mutex semaphore
            arg.val=1;
            if(semctl(semid,0,SETVAL,arg)==-1)
            {
            perror("setting semaphore value failed\n");
                return -1;
                }
            //set value for synchronous semaphore
            arg.val=num;
                //the num means that the producer can continue to produce num products
            if(semctl(semid,1,SETVAL,arg)==-1)
                {
            perror("setting semaphore value failed\n");
                return -1;
            }
            //the last semaphore's value is default
            //the default value '0' means that the consumer is not use any product now
    }

基本上这样，就算完成了生产者和消费者的前期工作。我们可以看到，在核心代码中，我们只需要“装模作样”的将代码“各就各位”即可，当然这需要你理解生产者消费者这个基本模型。而在下面的准备代码中，则需要我们理解关于信号量和共享内存的一些基本函数。

最后再说说使用，建议先运行一个生产者和一个消费者，观察两者是如何协调工作的。然后再只运行一个生产者或一个消费者，看其是否会阻塞。了解了以上情况后，你就可以同时运行多个生产者和消费者了。

下面是源代码：

shm.h

#include
#include
#include
#include
#include
#include
#include
#include
#include

#define SHM_SIZE 1024

union semun
{
    int val;
    struct semid_ds *buf;
    unsigned short *array;
};

//create a semaphore set
int createsem(const char *pathname,int proj_id,int num,int init_val)
{
    key_t key;
    int i,semid;
    union semun arg;

    if((key=ftok(pathname,proj_id))==-1)
    {
        perror(”ftok error:”);
        return -1;
    }

    if((semid=semget(key,num,IPC_CREAT|IPC_EXCL|0666))==-1)
    {
        return -1;
    }

    //initialize the value of semaphore
    arg.val=init_val;
    for(i=0;i
    {
        if(semctl(semid,i,SETVAL,arg)==-1)
        {
            perror(”semctl error:”);
            return -1;
        }
    }

    return (semid);
}

//open the semaphore set
int opensem(const char*pathname,int proj_id)
{
    key_t key;
    int semid;

    if((key=ftok(pathname,proj_id))==-1)
    {
        perror(”ftok error:”);
        return -1;
    }

    //just get the id of semaphore set
    if((semid=semget(key,0,IPC_CREAT|0666))==-1)
    {
        perror(”semget error:”);
        return -1;
    }

    return (semid);
}

//P operation
int p(int semid,int index)
{
    struct sembuf buf={0,-1,0};

    if(index<0)
    {
        printf(”error:the index is invalid\n”);
        return -1;
    }

    buf.sem_num=index;
    if(semop(semid,&buf,1)==-1)
    {
        perror(”semop error:”);
        return -1;
    }

    return 1;

}

//V opeation
int v(int semid,int index)
{
    struct sembuf buf={0,+1,0};

    if(index<0)
    {
        printf(”error:the index is invalid\n”);
        return -1;
    }

    buf.sem_num=index;
    if(semop(semid,&buf,1)==-1)
    {
        perror(”semop error:”);
        return -1;
    }

    return 1;
}

//delete the semaphore set
int deletesem(int semid)
{
    return (semctl(semid,0,IPC_RMID,0)==-1);
}

//waiting for the semaphore is equal to 1
int waitsem(int semid,int index)
{
    while(semctl(semid,index,GETVAL,0)==0)
    {
        sleep(1);
        printf(”I am waiting for semval equals 1..\n”);
    }
    return 1;
}

//create share memory
int createshm(char *pathname,int proj_id,size_t size)
{
    key_t key;
    int shmid;

    if((key=ftok(pathname,proj_id))==-1)
    {
        perror(”ftok error:”);
        return -1;
    }

    if((shmid=shmget(key,size,IPC_CREAT|IPC_EXCL|0666))==-1)
    {
        return -1;
    }

    return (shmid);
}
//open share memory
int openshm(char *pathname,int proj_id)
{
    key_t key;
    int shmid;

    if((key=ftok(pathname,proj_id))==-1)
    {
        perror(”ftok error:”);
        return -1;
    }

    if((shmid=shmget(key,0,IPC_CREAT|0666))==-1)
    {
        perror(”shmget error:”);
        return -1;
    }

    return (shmid);
}

#include 

#include #include #include #include #include #include #include #include #define SHM_SIZE 1024 union semun { int val; struct semid_ds *buf; unsigned short *array; }; //create a semaphore set int createsem(const char *pathname,int proj_id,int num,int init_val) { key_t key; int i,semid; union semun arg; if((key=ftok(pathname,proj_id))==-1) { perror(“ftok error:”); return -1; } if((semid=semget(key,num,IPC_CREAT|IPC_EXCL|0666))==-1) { return -1; } //initialize the value of semaphore arg.val=init_val; for(i=0;i 

producer.c

#include “shm.h”


int main()
{
    int num;
    int shmid_goods,shmid_index,semid;
    char* shmaddr=NULL;
    int *indexaddr=NULL;
    int is_noexist=0;

    num=10;
    //create a shared memory as goods buffer
    if((shmid_goods=createshm(“.”,’s’,num))==-1)
    {
        if(errno==EEXIST)
        {
            if((shmid_goods=openshm(“.”,’s’))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror(”create shared memory failed\n”);
                exit(1);
        }
    }
    //attach the shared memory to the current process
    if((shmaddr=shmat(shmid_goods,(char*)0,0))==(char*)-1)
    {
        perror(”attach shared memory error\n”);
        exit(1);
    }

    //create a shared memory as index
    if((shmid_index=createshm(“.”,‘z’,2))==-1)
    {
        if(errno==EEXIST)
        {
            if((shmid_index=openshm(“.”,‘z’))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror(”create shared memory failed\n”);
                exit(1);
        }
    }
    else
    {
        is_noexist=1;
    }
    //attach the shared memory to the current process
    if((indexaddr=shmat(shmid_index,(int*)0,0))==(int*)-1)
    {
        perror(”attach shared memory error\n”);
        exit(1);
    }
    if(is_noexist)
    {
        indexaddr[0]=0;
        indexaddr[1]=0;
    }

    //create a semaphore set including 3 semaphores
    if((semid=createsem(“.”,‘t’,3,0))==-1)
    {
        if(errno==EEXIST)
        {
            if((semid=opensem(“.”,‘t’))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror(”semget error:”);
            exit(1);
        }
    }
    else
    {
        union semun arg;
            //seting value for mutex semaphore
            arg.val=1;
            if(semctl(semid,0,SETVAL,arg)==-1)
            {
            perror(”setting semaphore value failed\n”);
                return -1;
                }
            //set value for synchronous semaphore
            arg.val=num;
                //the num means that the producer can continue to produce num products
            if(semctl(semid,1,SETVAL,arg)==-1)
                {
            perror(”setting semaphore value failed\n”);
                return -1;
            }
            //the last semaphore’s value is default
            //the default value ‘0’ means that the consumer is not use any product now
        }


    int goods=0;
    while(1)
    {
        p(semid,1);
        sleep(3);
        p(semid,0);
        //producer is producing a product
        goods=rand()%10;
        shmaddr[indexaddr[0]]=goods;
        printf(”producer:%d produces a product[%d]:%d\n”,getpid(),indexaddr[0],goods);
        indexaddr[0]=(indexaddr[0]+1)%10;
        v(semid,0);
        sleep(3);
        v(semid,2);
    }

}

#include "shm.h"


int main()
{
    int num;
    int shmid_goods,shmid_index,semid;
    char* shmaddr=NULL;
    int *indexaddr=NULL;
    int is_noexist=0;

    num=10;
    //create a shared memory as goods buffer
    if((shmid_goods=createshm(".",'s',num))==-1)
    {
        if(errno==EEXIST)
        {
            if((shmid_goods=openshm(".",'s'))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror("create shared memory failed\n");
                exit(1);
        }
    }
    //attach the shared memory to the current process
    if((shmaddr=shmat(shmid_goods,(char*)0,0))==(char*)-1)
    {
        perror("attach shared memory error\n");
        exit(1);
    }

    //create a shared memory as index
    if((shmid_index=createshm(".",'z',2))==-1)
    {
        if(errno==EEXIST)
        {
            if((shmid_index=openshm(".",'z'))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror("create shared memory failed\n");
                exit(1);
        }
    }
    else
    {
        is_noexist=1;
    }
    //attach the shared memory to the current process
    if((indexaddr=shmat(shmid_index,(int*)0,0))==(int*)-1)
    {
        perror("attach shared memory error\n");
        exit(1);
    }
    if(is_noexist)
    {
        indexaddr[0]=0;
        indexaddr[1]=0;
    }

    //create a semaphore set including 3 semaphores
    if((semid=createsem(".",'t',3,0))==-1)
    {
        if(errno==EEXIST)
        {
            if((semid=opensem(".",'t'))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror("semget error:");
            exit(1);
        }
    }
    else
    {
        union semun arg;
            //seting value for mutex semaphore
            arg.val=1;
            if(semctl(semid,0,SETVAL,arg)==-1)
            {
            perror("setting semaphore value failed\n");
                return -1;
                }
            //set value for synchronous semaphore
            arg.val=num;
                //the num means that the producer can continue to produce num products
            if(semctl(semid,1,SETVAL,arg)==-1)
                {
            perror("setting semaphore value failed\n");
                return -1;
            }
            //the last semaphore's value is default
            //the default value '0' means that the consumer is not use any product now
        }


    int goods=0;
    while(1)
    {
        p(semid,1);
        sleep(3);
        p(semid,0);
        //producer is producing a product
        goods=rand()%10;
        shmaddr[indexaddr[0]]=goods;
        printf("producer:%d produces a product[%d]:%d\n",getpid(),indexaddr[0],goods);
        indexaddr[0]=(indexaddr[0]+1)%10;
        v(semid,0);
        sleep(3);
        v(semid,2);
    }

}

 

consumer.c

#include “shm.h”


int main(int argc,char **argv)
{
    int num;
    int shmid_goods,shmid_index,semid;
    char* shmaddr=NULL;
    int* indexaddr=NULL;
    int is_noexist=0;

    num=10;
    //create a shared memory as goods buffer
    if((shmid_goods=createshm(“.”,’s’,num))==-1)
    {
        if(errno==EEXIST)
        {
            if((shmid_goods=openshm(“.”,’s’))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror(”create shared memory failed\n”);
                exit(1);
        }
    }
    //attach the shared memory to the current process
    if((shmaddr=shmat(shmid_goods,(char*)0,0))==(char*)-1)
    {
        perror(”attach shared memory error\n”);
        exit(1);
    }

    //create a shared memory as index
    if((shmid_index=createshm(“.”,‘z’,2))==-1)
    {
        if(errno==EEXIST)
        {
            if((shmid_index=openshm(“.”,‘z’))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror(”create shared memory failed\n”);
                exit(1);
        }
    }
    else
    {
        is_noexist=1;
    }
    //attach the shared memory to the current process
    if((indexaddr=shmat(shmid_index,(int*)0,0))==(int*)-1)
    {
        perror(”attach shared memory error\n”);
        exit(1);
    }
    if(is_noexist)
    {
        indexaddr[0]=0;
        indexaddr[1]=0;
    }

    //create a semaphore set including 3 semaphores
    if((semid=createsem(“.”,‘t’,3,0))==-1)
    {
        if(errno==EEXIST)
        {
            if((semid=opensem(“.”,‘t’))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror(”semget error:”);
            exit(1);
        }
    }
    else
    {
        union semun arg;
            //seting value for mutex semaphore
            arg.val=1;
            if(semctl(semid,0,SETVAL,arg)==-1)
            {
            perror(”setting semaphore value failed\n”);
                return -1;
                }
            //set value for synchronous semaphore
            arg.val=num;
                //the num means that the producer can continue to produce num products
            if(semctl(semid,1,SETVAL,arg)==-1)
                {
            perror(”setting semaphore value failed\n”);
                return -1;
            }
            //the last semaphore’s value is default
            //the default value ‘0’ means that the consumer is not use any product now
    }

    int goods=0;
    while(1)
    {
        p(semid,2);
        sleep(1);
        p(semid,0);
        //consumer is consuming a product
        goods=shmaddr[indexaddr[1]];
        printf(”consumer:%d consumes a product[%d]:%d\n”,getpid(),indexaddr[1],goods);
        indexaddr[1]=(indexaddr[1]+1)%num;
        v(semid,0);
        sleep(1);
        v(semid,1);
    }

}

#include "shm.h"


int main(int argc,char **argv)
{
    int num;
    int shmid_goods,shmid_index,semid;
    char* shmaddr=NULL;
    int* indexaddr=NULL;
    int is_noexist=0;

    num=10;
    //create a shared memory as goods buffer
    if((shmid_goods=createshm(".",'s',num))==-1)
    {
        if(errno==EEXIST)
        {
            if((shmid_goods=openshm(".",'s'))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror("create shared memory failed\n");
                exit(1);
        }
    }
    //attach the shared memory to the current process
    if((shmaddr=shmat(shmid_goods,(char*)0,0))==(char*)-1)
    {
        perror("attach shared memory error\n");
        exit(1);
    }

    //create a shared memory as index
    if((shmid_index=createshm(".",'z',2))==-1)
    {
        if(errno==EEXIST)
        {
            if((shmid_index=openshm(".",'z'))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror("create shared memory failed\n");
                exit(1);
        }
    }
    else
    {
        is_noexist=1;
    }
    //attach the shared memory to the current process
    if((indexaddr=shmat(shmid_index,(int*)0,0))==(int*)-1)
    {
        perror("attach shared memory error\n");
        exit(1);
    }
    if(is_noexist)
    {
        indexaddr[0]=0;
        indexaddr[1]=0;
    }

    //create a semaphore set including 3 semaphores
    if((semid=createsem(".",'t',3,0))==-1)
    {
        if(errno==EEXIST)
        {
            if((semid=opensem(".",'t'))==-1)
            {
                exit(1);
            }
        }
        else
        {
            perror("semget error:");
            exit(1);
        }
    }
    else
    {
        union semun arg;
            //seting value for mutex semaphore
            arg.val=1;
            if(semctl(semid,0,SETVAL,arg)==-1)
            {
            perror("setting semaphore value failed\n");
                return -1;
                }
            //set value for synchronous semaphore
            arg.val=num;
                //the num means that the producer can continue to produce num products
            if(semctl(semid,1,SETVAL,arg)==-1)
                {
            perror("setting semaphore value failed\n");
                return -1;
            }
            //the last semaphore's value is default
            //the default value '0' means that the consumer is not use any product now
    }

    int goods=0;
    while(1)
    {
        p(semid,2);
        sleep(1);
        p(semid,0);
        //consumer is consuming a product
        goods=shmaddr[indexaddr[1]];
        printf("consumer:%d consumes a product[%d]:%d\n",getpid(),indexaddr[1],goods);
        indexaddr[1]=(indexaddr[1]+1)%num;
        v(semid,0);
        sleep(1);
        v(semid,1);
    }

}

 

生产者消费者问题是操作系统中的一个经典的问题。

他描述的是一个，多个生产者与多个消费者共享多个缓冲区的事情，具体的定义百度。

然后看了操作系统的书籍如何解决书上给的伪代码是这样的

item B[k];
semaphore empty;    empty=k;   //可以使用的空缓冲区数
semaphore full; full=0;        //缓冲区内可以使用的产品数
semaphore mutex;    mutex=1;   //互斥信号量
int in=0;                      //放入缓冲区指针
int out=0;                     //取出缓冲区指针 
cobegin
process producer_i ( ) {        process consumer_j( )   {    
       while(true) {                 while(true) {
       produce( );                   P(full);
       P(empty);                     P(mutex);
       P(mutex);                     take( ) from B[out];
       append to B[in];              V(empty);             
       in=(in+1)%k;                  out=(out+1)%k;     
       V(mutex);                     V(mutex);  
       V(full);                      consume( );
                  }                               }
                    }                                }
coend
     
     
     
     

      
      
      
      
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上面的注释，和过程已经比较到位了，只是我习惯用我的方法，即把生产和消费，放入临界区所以下面是我解决生产消费模型所用的伪代码

item B[k];
semaphore empty;    empty=k;   //可以使用的空缓冲区数
semaphore full; full=0;        //缓冲区内可以使用的产品数
semaphore mutex;    mutex=1;   //互斥信号量
int in=0;                      //放入缓冲区指针
int out=0;                     //取出缓冲区指针 
cobegin
process producer_i ( ) {        process consumer_j( )   {    
       while(true) {                  while(true) {
       P(empty);                      P(full);
       P(mutex);                      P(mutex);
       produce( );                    take( ) from B[out];
       append to B[in];               consume( );               
       in=(in+1)%k;                   out=(out+1)%k;     
       V(mutex);                      V(mutex);  
       V(full);                       V(empty);
                  }                               }
                    }                                }
coend
     
     
     
     

      
      
      
      
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好了说了这么多我该帖下我的代码了，此代码在Linux环境下的多线程操作，用到了信号量的。。。

#include 
#include 
#include 
#include 

#include 
#include 
#include 
#include 

#define ERR_EXIT(m) \
        do \
        { \
                perror(m); \
                exit(EXIT_FAILURE); \
        } while(0)

#define CONSUMERS_COUNT 2   //消费者人数
#define PRODUCERS_COUNT 2   //生产者人数 
#define BUFFSIZE 5         

int g_buffer[BUFFSIZE];    //缓冲区数目

unsigned short in = 0;      //放入产品的指针（生产到哪个缓冲区）
unsigned short out = 0;     //取出缓冲区指针 （在哪个缓冲区消费的）
unsigned short produce_id = 0;     
unsigned short consume_id = 0;

sem_t g_sem_full; //可以使用的空缓冲区数（缓冲区中可以生产多少产品）
sem_t g_sem_empty;  //缓冲区内可以使用的产品数（可以消费的产品数）
pthread_mutex_t g_mutex;  //互斥信号量

pthread_t g_thread[CONSUMERS_COUNT + PRODUCERS_COUNT];

void *consume(void *arg)
{
    int i;
    int num = (int)arg;
    while (1)
    {
        printf("%d wait buffer not empty\n", num);
        sem_wait(&g_sem_empty);
        pthread_mutex_lock(&g_mutex);
        //遍历缓冲区，看有哪些缓冲区是可以生产产品的
        for (i = 0; i < BUFFSIZE; i++)
        {
            printf("%02d ", i);
            if (g_buffer[i] == -1)
                printf("%s", "null");
            else
                printf("%d", g_buffer[i]);

            if (i == out)
                printf("\t<--consume");

            printf("\n");
        }
        //produce()操作(生产产品)
        consume_id = g_buffer[out];
        printf("%d begin consume product %d\n", num, consume_id);
        g_buffer[out] = -1;
        //将取出缓冲区的指针偏移1（下个生产的位置）
        out = (out + 1) % BUFFSIZE;
        printf("%d end consume product %d\n", num, consume_id);
        pthread_mutex_unlock(&g_mutex);
        sem_post(&g_sem_full);
        sleep(1);
    }
    return NULL;
}

void *produce(void *arg)
{
    int num = (int)arg;
    int i;
    while (1)
    {
        printf("%d wait buffer not full\n", num);
        sem_wait(&g_sem_full);
        pthread_mutex_lock(&g_mutex);
        for (i = 0; i < BUFFSIZE; i++)
        {
            printf("%02d ", i);
            if (g_buffer[i] == -1)
                printf("%s", "null");
            else
                printf("%d", g_buffer[i]);

            if (i == in)
                printf("\t<--produce");

            printf("\n");
        }

        printf("%d begin produce product %d\n", num, produce_id);
        g_buffer[in] = produce_id;
        in = (in + 1) % BUFFSIZE;
        printf("%d end produce product %d\n", num, produce_id++);
        pthread_mutex_unlock(&g_mutex);
        sem_post(&g_sem_empty);
        sleep(5);
    }
    return NULL;
}

int main(void)
{
    int i;
    for (i = 0; i < BUFFSIZE; i++)
        g_buffer[i] = -1;

    sem_init(&g_sem_full, 0, BUFFSIZE);
    sem_init(&g_sem_empty, 0, 0);

    pthread_mutex_init(&g_mutex, NULL);


    for (i = 0; i < CONSUMERS_COUNT; i++)
        pthread_create(&g_thread[i], NULL, consume, (void *)i);

    for (i = 0; i < PRODUCERS_COUNT; i++)
        pthread_create(&g_thread[CONSUMERS_COUNT + i], NULL, produce, (void *)i);

    for (i = 0; i < CONSUMERS_COUNT + PRODUCERS_COUNT; i++)
        pthread_join(g_thread[i], NULL);

    sem_destroy(&g_sem_full);
    sem_destroy(&g_sem_empty);
    pthread_mutex_destroy(&g_mutex);

    return 0;
}
     
     
     
     

      
      
      
      
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将程序运行，可得到这个结果

(function () { ('pre.prettyprint code').each(function () { var lines = (this).text().split(′\n′).length;var numbering = $('

').addClass('pre-numbering').hide(); (this).addClass(′has−numbering′).parent().append( numbering); for (i = 1; i