C中的共享内存和MAP_ANONYMOUS缺失？

Question

我正在写一个C程序，我正在向n个玩家发牌，由n个分叉过程表示。我希望他们都共用同一副牌，所以我试图使用mmap()来跟踪牌组大小，但是我必须编译该程序的机器不允许MAP_ANONYMOUS或MAP_ANON。是否还有另一种方法可以将共享内存中的全局变量存储到C89/pre Linux 2.4中？

我的上下文程序：

static int *deck_size; 

int pop(int *arr, int *size, int loc) 
{ 
    int i; 
    int val = arr[loc]; 
    for(i = loc; i < (*size - 1); i++) 
    { 
     arr[i] = arr[(i+1)]; 
     arr[*size] = '\0'; 
    } 
    *size = *size-1; 
    return val; 
} 

int main(int argc, char* argv[]) 
{ 
    pid_t pid, wpid; 
    int status, index, players, rdm_card; 
    char outbuf[100]; 
    int deck[] = 
    {1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,6,6,6,6,7,7,7,7,8,8,8,8,9,9,9,9,10,10,10,10,11,11,11,11,12,12,12,12,13,13,13,13}; 

    deck_size = mmap(NULL, sizeof *deck_size, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0); 
    *deck_size = 52; 
    /* reject an execution with no arguments */ 
    if(argv[1] == NULL) 
    { 
     write(STDERR_FILENO, "Usage: dealer <n>\n", 18); 
     exit(EXIT_FAILURE); 
    } 
    else 
    { 
     if((players = atoi(argv[1])) < 1) 
     { 
      write(STDERR_FILENO, "n cannot be less than 1\n", 24); 
      exit(EXIT_FAILURE); 
     } 
    } 

    srand (time(NULL)); 

    rdm_card = rand() % *deck_size; 

    for(index = 0; index < players; index++) 
    { 
     pid = fork(); 
     if (pid == 0) { 
      sprintf(outbuf, "random card: %d\n", pop(deck, deck_size, rdm_card)); 
      write(STDOUT_FILENO, outbuf, 17); 
      printf("size of deck %d!\n", *deck_size); 
      exit(EXIT_SUCCESS); 
     } else if (pid < 0) { 
      write(STDERR_FILENO, "fork error\n", 11); 
      exit(EXIT_FAILURE); 
     } else { 
      do { 
       wpid = waitpid(pid, &status, WUNTRACED); 
      } while (!WIFEXITED(status) && !WIFSIGNALED(status)); 
     } 
    } 
    return 0; 
} 

Answer 1

当你清楚地阅读手册页MMAP(2)它明确规定，因为Linux内核2.4是MAP_ANONYMOUS支持。

只是因为2.4内核结合使用 MAP_ANONYMOUS与MAP_SHARED被支持的Linux 。

确保您定义_BSD_SOURCE或_SVID_SOURCE得到MAP_ANONYMOUS

#define _BSD_SOURCE