[Linux] 进程管理

/***
loop_wait.c
***/
#include <bits/stdc++.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <unistd.h>

// WARNING: Only signal-safe functions can be used in sig_handler.
// static void sig_handler(int signo) {
//   if (signo == SIGCHLD) {
//     pid_t pid;
//     while ((pid = waitpid(-1, NULL, WNOHANG)) > 0) {
//     }
//   }

//   signal(signo, sig_handler);
// }

int main(int argc, char *argv[]) {
  // signal(SIGCHLD, sig_handler);

  int n = 5, i;  //默认创建3个子进程
  pid_t p, q;

  std::set<pid_t> set;

  for (i = 0; i < n; i++) {  //出口1,父进程专用出口
    p = fork();
    if (p == 0) {
      break;  //出口2,子进程出口,i不自增
    } else {
      set.insert(p);
    }
  }

  if (n == i) {
    // sleep(n);
    printf("I am parent, pid = %d
", getpid(), getgid());
    // pid_t pid = waitpid(q, NULL, WNOHANG);
    //        pid_t pid = wait(NULL);
    // printf("child pid = %d
", pid);
    while (!set.empty()) {
      auto it = set.begin();

      while (it != set.end()) {
        auto pid = *it;
        int status;
        if ((waitpid(pid, &status, WNOHANG)) != 0) {
          printf("clean OK! pid :%d status: %d
", pid, status);
          printf("WEXITSTATUS(status) = %d
",
                 WEXITSTATUS(status));  //获取退出值
          printf("WIFEXITED(status) = %d
",
                 WIFEXITED(status));  //判断是否正常推出
          printf("WIFSIGNALED(status) = %d
",
                 WIFSIGNALED(status));  //判断是否被杀死
          set.erase(it++);
        } else {
          printf("pid still alive: %d
", pid);
          ++it;
        }

        // if (kill(pid, 0) != -1) {
        //   printf("pid still alive: %d", pid);
        //   ++it;
        // } else {
        //   printf("pid not alive, prepare for clean: %d
", pid);
        // }
      }
      sleep(1);
    }

  } else {
    sleep(i);
    printf("I'm %dth child, pid = %d, gpid=%d
", i + 1, getpid(), getgid());
    if (i == 1) {
      abort();
    } else if (i == 2) {
      std::vector<int> s;  // make crush
      printf("redeay to crush");
      s[10] = 10;
      printf("Not crush ??");
    } else {
      exit(i);
    }
  }

  return 0;
}