OS: Process: IPC: Shared Memory

19th November 2020 at 6:19pm
OS: Process: IPC

共享内存模型:

  • memory-mapped file,一个特殊的文件,用于被不同进程获取同一块关联的内存区域
  • shared-memory object,在代码中表示为一个指针,指向这块共享的内存区域

代码实例

Producer

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/shm.h>
#include <sys/stat.h>

int main() {
  /* the size (in bytes) of shared memory object */
  const int SIZE = 4096;
  /* name of the shared memory object */
  const char *name = "OS";
  /* strings written to shared memory */
  const char *message 0 = "Hello";
  const char *message 1 = "World!";
  /* shared memory file descriptor */
  int fd;
  /* pointer to shared memory obect */
  char *ptr;

  /* create the shared memory object */
  fd = shm_open(name, O CREAT | O RDWR, 0666);

  /* configure the size of the shared memory object */
  ftruncate(fd, SIZE);

  /* memory map the shared memory object */
  ptr = (char *)mmap(0, SIZE, PROT READ | PROT WRITE, MAP SHARED, fd, 0);

  /* write to the shared memory object */
  sprintf(ptr, "%s", message 0);
  ptr += strlen(message 0);
  sprintf(ptr, "%s", message 1);
  ptr += strlen(message 1);
  
  return 0;
}

Consumer

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/shm.h>
#include <sys/stat.h>

int main() {
  /* the size (in bytes) of shared memory object */
  const int SIZE = 4096;
  /* name of the shared memory object */
  const char *name = "OS";
  /* shared memory file descriptor */
  int fd;
  /* pointer to shared memory obect */
  char *ptr;

  /* open the shared memory object */
  fd = shm_open(name, O RDONLY, 0666);

  /* memory map the shared memory object */
  ptr = (char *)mmap(0, SIZE, PROT READ | PROT WRITE, MAP SHARED, fd, 0);

  /* read from the shared memory object */
  printf("%s", (char *)ptr);

  /* remove the shared memory object */
  shm_unlink(name);
  
  return 0;
}