如何使用Mmap共享内存.请更正我的代码

How to use Mmap to share memory. Please correct My code

本文关键字：我的 代码 内存 何使用 Mmap 共享      更新时间：2023-10-16

这里的问题是，我希望我们的看跌期权是93。我想让所有线程共享这个变量。就像静态变量对所有对象都是通用的一样，我想要一个对所有线程都通用的变量。

#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
static int *glob_var; 
int main(void)
  {
  glob_var = (int*)mmap(NULL, sizeof *glob_var, PROT_READ | PROT_WRITE, 
                MAP_SHARED | MAP_ANONYMOUS, -1, 0);
  *glob_var = 1;
  int ppid =fork();
  if (ppid == 0) {
     *glob_var = 92;  printf("%dn", *glob_var);
  } else if(ppid!=0){
     (*glob_var)++; /////I want a 93 over here???
      printf("%dn", *glob_var); /////I want a 93 over here??? print
      munmap(glob_var, sizeof *glob_var);
  }
  return 0;
  }

两个进程都更新glob_var。您需要协调对这个共享内存的访问。需要保证数据修改的顺序，即先赋值92。

信号量通常用于在以下情况下同步操作:

#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/wait.h> 
#include <sys/ipc.h>
#include <sys/sem.h>
#include <unistd.h>
// Binary semaphore implementation. Initial state 0
union semun 
{
  int val;
  struct semid_ds *buf;
  unsigned short int *array;
  struct seminfo *__buf;
};
int binary_semaphore_allocation (key_t key, int sem_flags)
{
  return semget (key, 1, sem_flags);
}
int binary_semaphore_deallocate (int semid)
{
  union semun ignored_argument;
  return semctl (semid, 1, IPC_RMID, ignored_argument);
}
int binary_semaphore_initialize (int semid)
{
  union semun argument;
  unsigned short values[1];
  values[0] = 0;
  argument.array = values;
  return semctl (semid, 0, SETALL, argument);
}
int binary_semaphore_wait (int semid)
{
  struct sembuf operations[1];
  operations[0].sem_num = 0;
  /* Decrement by 1. */
  operations[0].sem_op = -1;
  operations[0].sem_flg = SEM_UNDO;
  return semop (semid, operations, 1);
}
int binary_semaphore_post (int semid)
{
  struct sembuf operations[1];
  operations[0].sem_num = 0;
  /* Increment by 1. */
  operations[0].sem_op = 1;
  operations[0].sem_flg = SEM_UNDO;
  return semop (semid, operations, 1);
}
int main(void)
{
  key_t ipc_key;
  ipc_key = ftok(".", 'S');
  int sem_id;
  glob_var = (int*)mmap(NULL, sizeof *glob_var, PROT_READ | PROT_WRITE, 
                MAP_SHARED | MAP_ANONYMOUS, -1, 0);
  *glob_var = 1;
  if ((sem_id=binary_semaphore_allocation(ipc_key, IPC_CREAT|IPC_EXCL)) != -1) 
  {
    if (binary_semaphore_initialize(sem_id) == -1) 
    {
      printf("Semaphore initialization failed");
      return 2;
    }
  }
  int ppid = fork();
  if (ppid == 0)
  {
    if ((sem_id = binary_semaphore_allocation(ipc_key, 0)) == -1) 
    {
      printf("Child process failed to open semaphore");
      return 3;
    }
  }
  else
  {
    // Wait in parent process until child update glob_var
    binary_semaphore_wait(sem_id);
  }
  if (ppid == 0) 
  {
    *glob_var = 92;  
    printf("%dn", *glob_var);
    binary_semaphore_post(sem_id);
  }
  else if(ppid!=0)
  {
    (*glob_var)++; 
    printf("%dn", *glob_var); 
    munmap(glob_var, sizeof *glob_var);
    binary_semaphore_deallocate(sem_id);
  }
  return 0;
}
输出:

92
93
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