linux共享内存
1) 创建共享内存
int shmget(key_t key ,int size,int shmflg)
key标识共享内存的键值:0/IPC_PRIVATE。当key的取值为IPC_PRIVATE,则函数shmget将创建一块新的共享内存;如果key的取值为0,而参数中又设置了IPC_PRIVATE这个标志,则同样会创建一块新的共享内存。
返回值:如果成功,返回共享内存表示符,如果失败,返回-1。
2) 映射共享内存
int shmat(int shmid,char *shmaddr,int flag)
参数:
shmid:shmget函数返回的共享存储标识符
flag:决定以什么样的方式来确定映射的地址(通常为0)
返回值:如果成功,则返回共享内存映射到进程中的地址;如果失败,则返回-1。
3) 共享内存解除映射
当一个进程不再需要共享内存时,需要把它从进程地址空间中多里。
int shmdt(char *shmaddr)
4) shmctl() 控制对这块共享内存的使用
#define TEXT_SZ 2048 struct shared_use_st { int written_by_you; char some_text[TEXT_SZ]; };
read.cpp
#include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> #include "shm_com.h" /* * 程序入口 * */ int main(void) { int running=1; void *shared_memory=(void *)0; struct shared_use_st *shared_stuff; int shmid; /*创建共享内存*/ shmid=shmget((key_t)1234,sizeof(struct shared_use_st),0666|IPC_CREAT); if(shmid==-1) { fprintf(stderr,"shmget failed\n"); exit(EXIT_FAILURE); } /*映射共享内存*/ shared_memory=shmat(shmid,(void *)0,0); if(shared_memory==(void *)-1) { fprintf(stderr,"shmat failed\n"); exit(EXIT_FAILURE); } printf("Memory attached at %X\n",(int)shared_memory); /*让结构体指针指向这块共享内存*/ shared_stuff=(struct shared_use_st *)shared_memory; /*控制读写顺序*/ shared_stuff->written_by_you=0; /*循环的从共享内存中读数据,直到读到“end”为止*/ while(running) { if(shared_stuff->written_by_you) { printf("You wrote:%s",shared_stuff->some_text); sleep(1); //读进程睡一秒,同时会导致写进程睡一秒,这样做到读了之后再写 shared_stuff->written_by_you=0; if(strncmp(shared_stuff->some_text,"end",3)==0) { running=0; //结束循环 } } } /*删除共享内存*/ if(shmdt(shared_memory)==-1) { fprintf(stderr,"shmdt failed\n"); exit(EXIT_FAILURE); } exit(EXIT_SUCCESS); }
write.cpp
#include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> #include "shm_com.h" /* * 程序入口 * */ int main(void) { int running=1; void *shared_memory=(void *)0; struct shared_use_st *shared_stuff; char buffer[BUFSIZ]; int shmid; /*创建共享内存*/ shmid=shmget((key_t)1234,sizeof(struct shared_use_st),0666|IPC_CREAT); if(shmid==-1) { fprintf(stderr,"shmget failed\n"); exit(EXIT_FAILURE); } /*映射共享内存*/ shared_memory=shmat(shmid,(void *)0,0); if(shared_memory==(void *)-1) { fprintf(stderr,"shmat failed\n"); exit(EXIT_FAILURE); } printf("Memory attached at %X\n",(int)shared_memory); /*让结构体指针指向这块共享内存*/ shared_stuff=(struct shared_use_st *)shared_memory; /*循环的向共享内存中写数据,直到写入的为“end”为止*/ while(running) { while(shared_stuff->written_by_you==1) { sleep(1);//等到读进程读完之后再写 printf("waiting for client...\n"); } printf("Ener some text:"); fgets(buffer,BUFSIZ,stdin); strncpy(shared_stuff->some_text,buffer,TEXT_SZ); shared_stuff->written_by_you=1; if(strncmp(buffer,"end",3)==0) { running=0; //结束循环 } } /*删除共享内存*/ if(shmdt(shared_memory)==-1) { fprintf(stderr,"shmdt failed\n"); exit(EXIT_FAILURE); } exit(EXIT_SUCCESS); }
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