pc1.c: 使用条件变量解决生产者、计算者、消费者问题
/*• 系统中有3个线程：生产者、计算者、消费者• 系统中有2个容量为4的缓冲区：buffer1、buffer2• 生产者生产'a'、'b'、'c'、‘d'、'e'、'f'、'g'、'h'八个字符，放入到buffer1• 计算者从buffer1取出字符，将小写字符转换为大写字符，放入到buffer2• 消费者从buffer2取出字符，将其打印到屏幕上
实现思路：设置两个大小为4的缓冲区，第一个为生产者和计算着共享，第二个为计算者和消费者共享。
1、生产者线程产生字符，将字符写入缓冲区buffer1中，并将指针后移，当缓冲区被写满是，将生产者线程挂起，唤醒计算者线程，等待缓冲区buffer1有空闲存储空间的时候再唤醒生产者线程。
2、计算者线程从buffer1中读取数据，并移动指针，并将读取的数据写入buffer2中，当buffer1有空闲时，唤醒生产者进程，当buffer2被写满时唤醒消费者进程。
3、消费者进程从buffer2中读取字符并输出，并移动指针，当buffer2有空闲的时候，唤醒计算者进程。
实现代码：
#include<stdio.h>#include<pthread.h>#include<unistd.h>#define CAPACITY 4char buffer1[4];char buffer2[4];int crea; //生产者 int comp1;//计算者 int comp2;//计算者 int cons; //消费者 int buffer1_is_empty(){return crea==comp1;}int buffer1_is_full(){return (crea+1)%CAPACITY==comp1;}int buffer2_is_empty(){return comp2==cons;}int buffer2_is_full(){return (cons+1)%CAPACITY==comp2;}int get_item1(){int item;item=buffer1[comp1];comp1=(comp1+1)%CAPACITY;return item;}int get_item2(){int item;item=buffer2[cons];cons=(cons+1)%CAPACITY;return item;}int put_item1(int item){buffer1[crea]=item;crea=(crea+1)%CAPACITY;}int put_item2(int item){buffer2[comp2]=item;comp2=(comp2+1)%CAPACITY;}pthread_mutex_t mutex1;pthread_cond_t wait_empty_buffer1;pthread_cond_t wait_full_buffer1;pthread_mutex_t mutex2;pthread_cond_t wait_empty_buffer2;pthread_cond_t wait_full_buffer2;#define ITEM_COUNT (CAPACITY *2)void *consumer(void *arg){int i;int item;for(i=0;i<ITEM_COUNT;i++){pthread_mutex_lock(&mutex2);while(buffer2_is_empty())pthread_cond_wait(&wait_full_buffer2,&mutex2);item=get_item2();printf(" consume item:%c\n",item);pthread_cond_signal(&wait_empty_buffer2);pthread_mutex_unlock(&mutex2);}return NULL;}void *computer(void *arg){int i;int item;for(i=0;i<ITEM_COUNT;i++){pthread_mutex_lock(&mutex1);while(buffer1_is_empty())pthread_cond_wait(&wait_full_buffer1,&mutex1);item=get_item1();printf("computer get item:%c\n",item);item-=32;pthread_cond_signal(&wait_empty_buffer1);pthread_mutex_unlock(&mutex1);pthread_mutex_lock(&mutex2);while(buffer2_is_full())pthread_cond_wait(&wait_empty_buffer2,&mutex2);put_item2(item);printf("computer put item:%c\n",item);pthread_cond_signal(&wait_full_buffer2);pthread_mutex_unlock(&mutex2);}return NULL;}void *create(void *arg){int i;int item;for(i=0;i<ITEM_COUNT;i++){pthread_mutex_lock(&mutex1);while(buffer1_is_full())pthread_cond_wait(&wait_empty_buffer1,&mutex1);item='a'+i;put_item1(item);printf("create item:%c\n",item);pthread_cond_signal(&wait_full_buffer1);pthread_mutex_unlock(&mutex1);}return NULL;}int main(){pthread_t consumer_tid;pthread_t computer_tid;pthread_mutex_init(&mutex1,NULL);pthread_mutex_init(&mutex2,NULL);pthread_cond_init(&wait_empty_buffer1,NULL);pthread_cond_init(&wait_full_buffer1,NULL);pthread_cond_init(&wait_empty_buffer2,NULL);pthread_cond_init(&wait_full_buffer2,NULL);pthread_create(&consumer_tid,NULL,consumer,NULL);pthread_create(&computer_tid,NULL,computer,NULL);create(NULL);pthread_join(consumer_tid,NULL);pthread_join(computer_tid,NULL);pthread_mutex_destroy(&mutex1);pthread_mutex_destroy(&mutex2);return 0;}
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