Linux信号量机制

1.编写生产者代码：

用gedit完成productor.c的编写：

#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <sys/types.h>#include <sys/ipc.h>#include <sys/sem.h>#include <errno.h>int sem_id; void init(){    key_t key;    int ret;    unsigned short sem_array[2];    union semun    {         int val;         struct semid_ds *buf;         unsigned short *array;    }arg;    key=ftok(".",'s');    sem_id=semget(key,2,IPC_CREAT|0644);    sem_array[0]=0;                  //identify the productor    sem_array[1]=100;           //identifythe space    arg.array = sem_array;    ret = semctl(sem_id, 0, SETALL,arg);    if (ret == -1)    {         printf("SETALL failed(%d)\n", errno);    }    printf("productor init is%d\n",semctl(sem_id,0,GETVAL));    printf("space init is%d\n\n",semctl(sem_id,1,GETVAL)); }void del(){    semctl(sem_id,IPC_RMID,0);} int main(int argc,char *argv[]){    struct sembuf sops[2];    sops[0].sem_num = 0;    sops[0].sem_op = 1;    sops[0].sem_flg = 0;    sops[1].sem_num = 1;    sops[1].sem_op = -1;    sops[1].sem_flg = 0;     init();    printf("this isproductor\n");    while(1)    {         printf("\n\nbeforeproduce:\n");         printf("productornumber is %d\n",semctl(sem_id,0,GETVAL));         printf("space numberis %d\n",semctl(sem_id,1,GETVAL));         semop(sem_id,(struct sembuf *)&sops[1],1);         //get the space to instore 。the productor         printf("nowproducing......\n");         semop(sem_id,(struct sembuf *)&sops[0],1);         //now tell the customer can bucusume         printf("\nafterproduce\n");         printf("spaces numberis %d\n",semctl(sem_id,1,GETVAL));         printf("productornumber is %d\n",semctl(sem_id,0,GETVAL));         sleep(2);    }    del();}2.编写消费者代码：用gedit完成sem.c的编写： #include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <sys/types.h>#include <sys/ipc.h>#include <sys/sem.h>#include <errno.h>int sem_id; void init(){    key_t key;    key=ftok(".",'s');    sem_id=semget(key,2,IPC_CREAT|0644);    //printf("sem id is%d\n",sem_id);}int main(int argc,char *argv[]){    init();    struct sembuf sops[2];    sops[0].sem_num = 0;    sops[0].sem_op = -1;    sops[0].sem_flg = 0;    sops[1].sem_num = 1;    sops[1].sem_op = 1;    sops[1].sem_flg = 0;    init();     printf("this iscustomer\n");    while(1)    {         printf("\n\nbeforeconsume:\n");         printf("productor is%d\n",semctl(sem_id,0,GETVAL));         printf("space  is %d\n",semctl(sem_id,1,GETVAL));         semop(sem_id,(struct sembuf *)&sops[0],1);         //get the productor to cusume         printf("nowconsuming......\n");         semop(sem_id,(struct sembuf *)&sops[1],1);         //now tell the productor can doproduce         printf("\nafterconsume\n");         printf("productsnumber is %d\n",semctl(sem_id,0,GETVAL));         printf("space numberis %d\n",semctl(sem_id,1,GETVAL));         sleep(2);    }} 

 

3. 讨论问题

1. 编译并运行上述程序，观察运行效果并解释原因？

生产者和消费者对缓冲区互斥访问是互斥关系，同时生产者和消费者又是一个相互协作的关系，只有生产者生产之后，消费者才能消费，他们也是同步关系。

2. 上述代码中，标黄的部分分别是什么意义？

用信号量来标记空间

通过调用semop函数来实现pv操作

Sleep表示生产或消费所需时间

3. 改变生产者、消费者的两项sleep的参数，观察两个进程的运行效果如何改变？

生产与消费不会保持平衡，货品会越来越多（少）

4. 如果同时运行多个生产者、消费者进程，执行情况如何？

可以等效的看成是sleep的数值不一，生产的数量和消费的数量不相称。