Process handle tips

一些處理行程的技巧

1.防止zombie process產生

http://home.educities.edu.tw/shirock/comp/Anti_zombie_process.htm

linux上的正解

int child_stat;

void reapchild() { 
  while( wait(&child_stat) <= 0 ) 
    /*NOTHING or your code*/; 
} 

. . . 
struct sigaction act; 
act.sa_handler = reapchild; 
act.sa_flags = SA_NOCLDSTOP; /* Do not signal while process paused */
sigaction( SIGCHLD, &act, NULL); 

這個方式不適合在寫library時用
只要用library的人去重設signal就完了

2.system(const char *string)的傳回值

system這個function的return value傳回的是fork process的return value
並不是所執行的程式傳回值.

要拿到執行的程式傳回值要用以下方式

  #include 

  int r;
  r = system("ifconfig eth0");
  if(WEXITSTATUS(r) == 1) /*Fail*/
    return;


2.Fork

  pid_t pid;
  if((pid = vfork()) == 0)  { /*Child*/
    execl("/bin/ping", "ping", "-c", "3", ip, (char *)0);
    _exit(127);
  } else if(pid < 0)
    perror("fork");
  else  /*Parent*/
    dev->ping->pid = pid;

  .......
  .......

  int status;
  pid_t pid = waitpid(dev->ping->pid, &status, WNOHANG);
  if(pid > 0)
  if(WIFEXITED(status)) {
   dev->ping->pid = 0;
   if(WEXITSTATUS(status) != 0)  {  /*ping without response*/
    SxNetDev_Fail(dev, "Ping fail");
    return;
  } else  {
    SxNetDev_Connect(dev);
    SxNetDev_Ping(dev, config->pppoe.ping);
  }
  }