深入了解进程间通信:System V 信号量 + 共享内存

前言： 共享内存 指 (shared memory)在多处理器的计算机系统中，可以被不同中央处理器（CPU）访问的大容量内存。由于多个CPU需要快速访问存储器，这样就要对存储器进行缓存（Cache）。

writer：

#include<sys/types.h>
#include<sys/ipc.h>
#include<sys/sem.h>
#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include<string.h>
#include<sys/shm.h>
#include<errno.h>
#defineSEM_KEY 4001
#defineSHM_KEY 5678
unionsemun {
intval;
};
intmain(void){
/*create a shm*/
intsemid,shmid;
shmid = shmget(SHM_KEY,sizeof(int),IPC_CREAT|0666);
if(shmid<0){
printf("create shm error\n");
return-1;
}
void* shmptr;
shmptr =shmat(shmid,NULL,0);
if(shmptr == (void*)-1){
printf("shmat error:%s\n",strerror(errno));
return-1;
}
int* data = (int*)shmptr;
semid = semget(SEM_KEY,2,0666);
structsembufsembuf1;
unionsemun semun1;
while(1){
sembuf1.sem_num=1;
sembuf1.sem_op=-1;
sembuf1.sem_flg=SEM_UNDO;
semop(semid,&sembuf1,1);
scanf("%d",data);
sembuf1.sem_num=0;
sembuf1.sem_op=1;
sembuf1.sem_flg=SEM_UNDO;
semop(semid,&sembuf1,1);
}
return0;
}

reader：

#include<sys/types.h>
#include<sys/ipc.h>
#include<sys/sem.h>
#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include<string.h>
#include<sys/shm.h>
#include<errno.h>
#defineSEM_KEY 4001
#defineSHM_KEY 5678
unionsemun {
intval;
};
intmain(void){
/*create a shm*/
intsemid,shmid;
shmid = shmget(SHM_KEY,sizeof(int),IPC_CREAT|0666);
if(shmid<0){
printf("create shm error\n");
return-1;
}
void* shmptr;
shmptr =shmat(shmid,NULL,0);
if(shmptr == (void*)-1){
printf("shmat error:%s\n",strerror(errno));
return-1;
}
int* data = (int*)shmptr;
semid = semget(SEM_KEY,2,IPC_CREAT|0666);
unionsemun semun1;
semun1.val=0;
semctl(semid,0,SETVAL,semun1);
semun1.val=1;
semctl(semid,1,SETVAL,semun1);
structsembufsembuf1;
while(1){
sembuf1.sem_num=0;
sembuf1.sem_op=-1;
sembuf1.sem_flg=SEM_UNDO;
semop(semid,&sembuf1,1);
printf("the NUM:%d\n",*data);
sembuf1.sem_num=1;
sembuf1.sem_op=1;
sembuf1.sem_flg=SEM_UNDO;
semop(semid,&sembuf1,1);
}
return0;
}

相关视频：

【Linux内核】Linux内核进程间通信组件的实现(上): https://www.zhihu.com/zvideo/1288126445278330880

【Linux内核】Linux内核进程间通信组件的实现(下) : https://www.zhihu.com/zvideo/1288128472473387008