13 共享内存3

来源：互联网发布：ubuntu启动程序命令编辑：程序博客网时间：2024/05/22 06:06

1. 删除进程中的地址映射shmdt

原型： int shmdt(const void *shmaddr)

参数： shmaddr共享内存映射后的地址

返回：成功0，出错-1

2. 删除共享内存对象shmctl

原型： int shmctl(int shmid, int cmd, struct shmid_ds * buf)

参数： shmid，要操作的共享内存标识符

cmd： IPC_STAT，获取对象属性值 //实现了命令ipcs -m

IPC_SET，设置对象属性

IPC_RMID，删除对象//实现了命令ipcrm -m

返回：成功0，出错-1

3. 实例一

通过ftok生成key，并创建共享内存；将共享内存映射到用户空间；写内存；读内存；之后删除；删除后在继续写共享内存，系统会报错

#include "sys/types.h"#include "sys/shm.h"#include "signal.h"#include "unistd.h"#include "stdio.h"#include "stdlib.h"#include "string.h"int main(){  int shmid;  int key;  char *p;  key=ftok("./a.c",'b');  if(key <0 )  {printf("creat key fialure\n");return -2;  }  printf("creat key sucess key=%X\n",key);  shmid=shmget(key,128,IPC_CREAT | 0777);  if(shmid <0)  {printf("creat share memory failure\n");return -1;  }  printf("creat share memory sucess shmid=%d\n",shmid);  system("ipcs -m");  p=(char *)shmat(shmid,NULL,0);  if(p == NULL)  {printf("shmat function failure\n");return -3;  }  //write share memory  fgets(p,128,stdin);  //start read share memory  printf("share memory data:%s",p);  printf("second read share memory data:%s",p);    shmdt(p);  memcpy(p,"abcd",4);  return 0;}

执行结果：

alex@alex-virtual-machine:/extra/process/thirteen$ gcc shmdt.calex@alex-virtual-machine:/extra/process/thirteen$ ./a.outcreat key sucess key=6211A055creat share memory sucess shmid=2195468------ Shared Memory Segments --------key        shmid      owner      perms      bytes      nattch     status0x00000000 950272     alex       600        524288     2          dest0x00000000 1867777    alex       600        524288     2          dest0x00000000 425986     alex       600        524288     2          dest0x00000000 458755     alex       600        524288     2          dest0x00000000 2064388    alex       600        524288     2          dest0x00000000 1572869    alex       600        33554432   2          dest0x00000000 2129926    alex       777        128        00x00000000 1081351    alex       600        16777216   20x00000000 1179656    alex       600        524288     2          dest0x00000000 2097161    alex       600        1048576    2          dest0x00000000 1409034    alex       600        524288     2          dest0x6211a066 2162699    alex       777        128        00x6211a055 2195468    alex       777        128        0helloshare memory data:hellosecond read share memory data:helloSegmentation fault (core dumped)alex@alex-virtual-machine:/extra/process/thirteen$

4. 实例二，操作完共享内存后，将对象删除

#include "sys/types.h"#include "sys/shm.h"#include "signal.h"#include "unistd.h"#include "stdio.h"#include "stdlib.h"#include "string.h"int main(){  int shmid;  int key;  char *p;  key=ftok("./a.c",'b');  if(key <0 )  {printf("creat key fialure\n");return -2;  }  printf("creat key sucess key=%X\n",key);  shmid=shmget(key,128,IPC_CREAT | 0777);  if(shmid <0)  {printf("creat share memory failure\n");return -1;  }  printf("creat share memory sucess shmid=%d\n",shmid);  system("ipcs -m");  p=(char *)shmat(shmid,NULL,0);  if(p == NULL)  {printf("shmat function failure\n");return -3;  }  //write share memory  fgets(p,128,stdin);  //start read share memory  printf("share memory data:%s",p);  printf("second read share memory data:%s",p);    shmdt(p); // memcpy(p,"abcd",4);  shmctl(shmid,IPC_RMID,NULL);  system("ipcs -m ");  return 0;}

执行结果：

alex@alex-virtual-machine:/extra/process/thirteen$ gcc shmctl.calex@alex-virtual-machine:/extra/process/thirteen$ lsa.c  a.out  myipcsrm  myipcsrm.c  shmctl.c  shmdt.calex@alex-virtual-machine:/extra/process/thirteen$ ./a.outcreat key sucess key=6211A055creat share memory sucess shmid=2195468------ Shared Memory Segments --------key        shmid      owner      perms      bytes      nattch     status0x00000000 950272     alex       600        524288     2          dest0x00000000 1867777    alex       600        524288     2          dest0x00000000 425986     alex       600        524288     2          dest0x00000000 458755     alex       600        524288     2          dest0x00000000 2064388    alex       600        524288     2          dest0x00000000 1572869    alex       600        33554432   2          dest0x00000000 2129926    alex       777        128        00x00000000 1081351    alex       600        16777216   20x00000000 1179656    alex       600        524288     2          dest0x00000000 2097161    alex       600        1048576    2          dest0x00000000 1409034    alex       600        524288     2          dest0x6211a066 2162699    alex       777        128        00x6211a055 2195468    alex       777        128        0helloshare memory data:hellosecond read share memory data:hello------ Shared Memory Segments --------key        shmid      owner      perms      bytes      nattch     status0x00000000 950272     alex       600        524288     2          dest0x00000000 1867777    alex       600        524288     2          dest0x00000000 425986     alex       600        524288     2          dest0x00000000 458755     alex       600        524288     2          dest0x00000000 2064388    alex       600        524288     2          dest0x00000000 1572869    alex       600        33554432   2          dest0x00000000 2129926    alex       777        128        00x00000000 1081351    alex       600        16777216   20x00000000 1179656    alex       600        524288     2          dest0x00000000 2097161    alex       600        1048576    2          dest0x00000000 1409034    alex       600        524288     2          dest0x6211a066 2162699    alex       777        128        0alex@alex-virtual-machine:/extra/process/thirteen$

5. 实例三，myipcsrm函数

#include "sys/types.h"#include "sys/shm.h"#include "signal.h"#include "unistd.h"#include "stdio.h"#include "stdlib.h"#include "string.h"int main(int argc,char *argv[]){  int shmid;  if(argc < 3)  {printf("please input param\n");return -1;  }  if(strcmp(argv[1],"-m") == 0)  printf("delete share memory");  else  return -2;  shmid=atoi(argv[2]);  printf("shmid=%d\n",shmid);  shmctl(shmid,IPC_RMID,NULL);  system("ipcs -m");  return 0;}

执行结果：

alex@alex-virtual-machine:/extra/process/thirteen$ gcc -o myipcsrm myipcsrm.calex@alex-virtual-machine:/extra/process/thirteen$ ./myipcsrmplease input paramalex@alex-virtual-machine:/extra/process/thirteen$ ipcs -m------ Shared Memory Segments --------key        shmid      owner      perms      bytes      nattch     status0x00000000 950272     alex       600        524288     2          dest0x00000000 1867777    alex       600        524288     2          dest0x00000000 425986     alex       600        524288     2          dest0x00000000 458755     alex       600        524288     2          dest0x00000000 2064388    alex       600        524288     2          dest0x00000000 1572869    alex       600        33554432   2          dest0x00000000 2129926    alex       777        128        00x00000000 1081351    alex       600        16777216   20x00000000 1179656    alex       600        524288     2          dest0x00000000 2097161    alex       600        1048576    2          dest0x00000000 1409034    alex       600        524288     2          dest0x6211a066 2162699    alex       777        128        0alex@alex-virtual-machine:/extra/process/thirteen$ ./myipcsrm 2162699please input paramalex@alex-virtual-machine:/extra/process/thirteen$ ./myipcsrm -m 2162699delete share memoryshmid=2162699------ Shared Memory Segments --------key        shmid      owner      perms      bytes      nattch     status0x00000000 950272     alex       600        524288     2          dest0x00000000 1867777    alex       600        524288     2          dest0x00000000 425986     alex       600        524288     2          dest0x00000000 458755     alex       600        524288     2          dest0x00000000 2064388    alex       600        524288     2          dest0x00000000 1572869    alex       600        33554432   2          dest0x00000000 2129926    alex       777        128        00x00000000 1081351    alex       600        16777216   20x00000000 1179656    alex       600        524288     2          dest0x00000000 2097161    alex       600        1048576    2          dest0x00000000 1409034    alex       600        524288     2          destalex@alex-virtual-machine:/extra/process/thirteen$

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