缓冲区进程互斥

【2016年北京大学自主命题831，第二（3）题】
有四个进程，R1，R2，W1，W2，一个共享缓冲器B，B可以存储一个字符，R1可以从磁盘写入一个字符到B，R2可以从寄存器写入一个字符到B，W1从B中取出一个字符送到打印机打印，W2将字符读出并送往显示器显示，B只能互斥使用。请你设计一个算法完成进程同步，说明你的信号量和初始值，并用PV操作描述代码。

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

//semaphores
sem_t  mutex,empty,full;

struct data {
    int id;
};

//R1
void* R1(void* param){
    // while(1){
    	int id = ((struct data*)param)->id;
        sem_wait(&empty);
        sem_wait(&mutex);
        printf("%d--R1--->B--began\n",id);
        sleep(5);
        printf("%d--R1--->B--finish\n",id);
        sem_post(&mutex);
        sem_post(&full);
    // }
}

//R2
void* R2(void* param){
    // while(1){
    	int id = ((struct data*)param)->id;
        sem_wait(&empty);
        sem_wait(&mutex);
        printf("%d--R2--->B--began\n",id);
        sleep(5);
        printf("%d--R2--->B--finish\n",id);
        sem_post(&mutex);
        sem_post(&full);
    // }
}

//W1
void* W1(void* param){
    while(1){
    	int id = ((struct data*)param)->id;
        sem_wait(&full);
        sem_wait(&mutex);
        printf("	B--->W1\n");
        sleep(5);
        sem_post(&mutex);
        sem_post(&empty);
    }
}

//W2
void* W2(void* param){
    while(1){
    	int id = ((struct data*)param)->id;
        sem_wait(&full);
        sem_wait(&mutex);
        printf("	B--->W2\n");
        sleep(5);
        sem_post(&mutex);
        sem_post(&empty);
    }
}

int main() {
    //pthread
    pthread_t tid; // the thread identifier 线程标识符

    pthread_attr_t attr; //set of thread attributes线程属性集

    /* get the default attributes获取默认属性 */
    pthread_attr_init(&attr);

    //initial the semaphores初始化信号量
    sem_init(&mutex, 0, 1);
    sem_init(&full, 0, 0);
    sem_init(&empty, 0, 1);

    int id = 0;
    while(scanf("%d", &id) != EOF) {

        char role;      //producer or consumer
        scanf("%c", &role);
        struct data* d = (struct data*)malloc(sizeof(struct data));
        d->id = id;
        if(role == 'r') {
            printf("    %d--R1->B--waiting\n",id);
            pthread_create(&tid, &attr, R1, d);
        }
        else if(role == 'R') {
            printf("    %d--R2->B--waiting\n",id);
            pthread_create(&tid, &attr, R2, d);
        }
        else if(role == 'w') {
            printf("    B->W1--waiting\n");
            pthread_create(&tid, &attr, W1, d);
        }
        else if(role == 'W') {
            printf("    B->W2--waiting\n");
            pthread_create(&tid, &attr, W2, d);
        }
    }

    //信号量销毁
    sem_destroy(&mutex);
    sem_destroy(&empty);
    sem_destroy(&full);
    return 0;
}