5、进程间通信-信号量

1、一个读取设置信号量集合的示例程序

code：

#include<stdio.h>#include<sys/types.h>#include<sys/sem.h>#include<errno.h>#define MAX_SEMAPHORES 5int main(){union semun// 参数联合体{int val;struct semid_ds * buf;unsigned short * array;//for GETALL and SETALL} arg;int semid=semget(IPC_PRIVATE,MAX_SEMAPHORES,IPC_CREAT|0666);//创建信号量集合if(semid!=-1){unsigned short sem_array[MAX_SEMAPHORES];int i;for(i=0;i<MAX_SEMAPHORES;i++)sem_array[i]=i+1;arg.array=sem_array;int ret=semctl(semid,0,SETALL,arg);//设置信号量-全部if(ret==-1)printf("failed %d/n",errno);unsigned short sem_read_array[MAX_SEMAPHORES];arg.array=sem_read_array;ret=semctl(semid,0,GETALL,arg);//读取信号量-全部if(ret==-1)printf("failed %d/n",errno);for(i=0;i<MAX_SEMAPHORES;i++)printf("Semaphore %d, value %d/n",i,sem_read_array[i]);for(i=0;i<MAX_SEMAPHORES;i++){ret=semctl(semid,i,GETVAL);//读取信号量-单个printf("Semaphore %d, value %d/n",i,ret);}ret=semctl(semid,0,IPC_RMID);//删除信号量集合}else printf("Could not allocate semaphore %d/n",errno);return 0;}

结果：

root@ubuntu:/code/chap9# ./run3Semaphore 0, value 1Semaphore 1, value 2Semaphore 2, value 3Semaphore 3, value 4Semaphore 4, value 5Semaphore 0, value 1Semaphore 1, value 2Semaphore 2, value 3Semaphore 3, value 4Semaphore 4, value 5

 

2、使用信号量 实现生产者-消费者问题

code：

生产者：

root@ubuntu:/code/chap9# cat producer.c#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()//建立信号量集合{key_t key;int ret;key=ftok(".",'s');sem_id=semget(key,2,IPC_CREAT|0644);union semun{int val;struct semid_ds * buf;unsigned short * array;}arg;unsigned short sem_array[2]={0,100};arg.array=sem_array;ret=semctl(sem_id,0,SETALL,arg);//初始化信号量，2个信号量，produt、spaceif(ret==-1)printf("setall failed %d/n",errno);printf("product init is %d/n",semctl(sem_id,0,GETVAL));printf("space init is %d/n",semctl(sem_id,1,GETVAL));}int main(){//操作两个信号量使用的结构体struct sembuf sop[2];sop[0].sem_num=0;//执行加1操作，每生产一个产品，对 product 加1sop[0].sem_op=1;sop[0].sem_flg=0;sop[1].sem_num=1;//执行减1操作，每生产一个产品，对 space 减1sop[1].sem_op=-1;sop[1].sem_flg=0;init();printf("this is productor/n");int count=1;while(1){printf("stage %d/nbefore produce:/n",count++);printf("product is %d/n",semctl(sem_id,0,GETVAL));printf("space is %d/n",semctl(sem_id,1,GETVAL));semop(sem_id,(struct sembuf*)&sop[1],1);//get the spaceprintf("now producing.../n");semop(sem_id,(struct sembuf*)&sop[0],1);//put the productprintf("after produce:/n");printf("product is %d/n",semctl(sem_id,0,GETVAL));printf("space is %d/n/n",semctl(sem_id,1,GETVAL));sleep(4);}return 0;}

消费者：

root@ubuntu:/code/chap9# cat customer.c#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);}int main(){init();struct sembuf sop[2];sop[0].sem_num=0;sop[0].sem_op=-1;sop[0].sem_flg=0;sop[1].sem_num=1;sop[1].sem_op=1;sop[1].sem_flg=0;printf("this is customer/n");int count=1;while(1){printf("stage %d:/nbefore sonsume:/n",count++);printf("product is %d/n",semctl(sem_id,0,GETVAL));printf("space is %d/n",semctl(sem_id,1,GETVAL));semop(sem_id,(struct sembuf*)&sop[0],1);//get the productprintf("now consuming.../n");semop(sem_id,(struct sembuf*)&sop[1],1);//increase the spaceprintf("after consume/n");printf("product is %d/n",semctl(sem_id,0,GETVAL));printf("space is %d/n/n",semctl(sem_id,1,GETVAL));sleep(3);}}

结果：

生产者：

stage 3before produce:product is 2space is 98now producing...after produce:product is 3space is 97stage 4before produce:product is 3space is 97now producing...after produce:product is 4space is 96

消费者：

stage 2:before sonsume:product is 9space is 91now consuming...after consumeproduct is 8space is 92stage 3:before sonsume:product is 9space is 91now consuming...after consumeproduct is 8space is 92