processes.cpp

//
//  main.c
//  processes
//
//  Created by AlexDenisov on 14.06.17.
//  Copyright © 2017 Low Level Bits. All rights reserved.
//

#include <assert.h>
#include <signal.h>
#include <unistd.h>

#include <iostream>
#include <chrono>
#include <thread>

using namespace std;

pid_t mullFork(const char *processName) {
  static int childrenCount = 0;
  childrenCount++;
  const pid_t pid = fork();
  if (pid == -1) {
    cout << "Failed to create " << processName
      << " after creating " << childrenCount
      << " child processes\n";
    cout << "Shutting down\n";
    exit(1);
  }
  return pid;
}

void do_fork() {
  const pid_t watchdogPID = mullFork("watchdog");
  if (watchdogPID == 0) {

    const pid_t timerPID = mullFork("timer");
    if (timerPID == 0) {
      std::this_thread::sleep_for(std::chrono::seconds(5));
      exit(0);
    }

    const pid_t workerPID = mullFork("worker");

    if (workerPID == 0) {
      std::this_thread::sleep_for(std::chrono::milliseconds(100));
      exit(42);
    }

    int status = 0;
    const pid_t exitedPID = waitpid(WAIT_ANY, &status, 0);
    if (exitedPID == timerPID) {
      /// Timer Process finished first, meaning that the worker timed out
      kill(workerPID, SIGKILL);
      cout << "Timed out\n";
    } else if (exitedPID == workerPID) {
      kill(timerPID, SIGKILL);
      /// Worker Process finished first
      /// Need to check whether it has signaled (crashed) or finished normally
      if (WIFSIGNALED(status)) {
        cout << "Crashed\n";
      }

      else if (WIFEXITED(status) && WEXITSTATUS(status) != 42) {
        cout << "Abnormal Exit\n";
      } else {
        cout << "All good\n";
      }
    } else {
      assert(0 && "Should not reach!");
    }

    wait(nullptr);
    exit(0);
  } else {
    pid_t pid = 0;
    while ( (pid = waitpid(watchdogPID, 0, 0)) == -1 ) {}
  }

  wait(0);
}

int main(int argc, const char * argv[]) {
  for (int i = 0; i < 10000; i++) {
    cout << i << " ";
    do_fork();
  }

  return 0;
}