C: Linux C 编程 - 共享内存

共享内存

共享内存段

即shared memory segment

 

分配共享内存段

shmget

函数原型

int shmget(key_t key, size_t size, int shmflg);

 

共享内存操控

即shared memory control

 

shmctl

函数原型

int shmctl(int shmid, int cmd, struct shmid_ds *buf);

 

共享内存操作

即shared memory operations

 

shmat

函数原型

void *shmat(int shmid, const void *shmaddr, int shmflg);

 

shmdt

函数原型

int shmdt(const void *shmaddr);

 

#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>

struct message
{
  int cmd;
  int uid;
  int state;
};

int main()
{
  int shmid;
  struct message *r_buf, *w_buf;

  shmid = shmget((key_t) 1, sizeof(struct message), 0666 | IPC_CREAT);
  if (shmid == -1)
  {
    printf("shmget error\n");
    return 1;
  }
  
  w_buf = (struct message *) shmat(shmid, NULL, 0);
  if (w_buf == (struct message *) -1)
  {
    printf("shmat error: for write buffer\n");
    return 1;
  }

  r_buf = (struct message *) shmat(shmid, w_buf, SHM_REMAP);
  if (r_buf == (struct message *) -1) 
  {
    printf("shmat error: for read buffer\n");
    return 1;
  }

  printf("shmaddr: %p(for write), %p(for read)\n", w_buf, r_buf);

  w_buf->cmd = 111;
  w_buf->uid = 1001011;
  w_buf->state = 2;

  printf("read: cmd=%d, uid=%d, state=%d\n", r_buf->cmd, r_buf->uid, r_buf->state);
  
  if (shmdt(w_buf)) 
  {
    printf("shmdt error: for write buffer\n");
    return 1;
  }
  
  // do not re- shmdt
  /*
  if (shmdt(r_buf)) 
  {
    printf("shmdt error: for read buffer\n");
    return 1;
  }
  */

  if (shmctl(shmid, IPC_RMID, NULL) == -1) 
  {
    printf("shmctl error\n");
    return 1;
  }
  return 0;
}