5.1: Processes | Add 'Zombie-checker' example

Author: mgroot

5_Processes_Signals_Files_Pipes/1_Processes/exec-cat.cpp renamed to 5_Processes_Signals_Files_Pipes/1_Processes/1_exec-cat.cpp

@@ -0,0 +1,124 @@
+#include <iostream>
+#include <unistd.h>
+#include <sys/wait.h>
+#include <signal.h>
+#include <random>
+
+#define CHILDS_NUMBER 10
+#define WORK_DELAY 2
+
+///////////////// CHILD
+
+int   childs_code(int number)
+{
+  /// set deed
+  std::srand(std::time(NULL));   // set personal seed
+  sleep(CHILDS_NUMBER - number); // wait for other processes
+
+  /// rand
+  int random_duration = 5 + std::rand() % 20;
+  std::cout << "\t[" << getpid() << "] is waiting for " 
+            << random_duration << " seconds" << std::endl;
+  
+  /// sleep
+  sleep(random_duration);
+
+  /// exit
+  exit(0);
+}
+
+
+
+///////////////// FORK
+
+int   create_childs()
+{
+  pid_t pid;
+
+  std::cout << "Creating child processes..." << std::endl;
+  for (int i = 0; i < CHILDS_NUMBER; ++i)
+  {
+    pid = fork();
+    if (!pid) 
+    {
+      childs_code(i);
+    }
+    else if (pid < 0)
+    {
+      std::cerr << "Fork failed!" << std::endl;
+      return 1;
+    }
+
+    sleep(1);
+  }
+  std::cout << "Creating done...\n" << std::endl;
+
+  return 0;
+}
+
+
+
+
+///////////////// MAIN PROCESS
+//////////// CHECK
+
+bool  check_zombies()
+{
+  /// begin
+  std::cout << "Start zombie checking..." << std::endl;
+  
+  // wait for processes
+  int pid, status;
+  while((pid = waitpid(-1, &status, WNOHANG)) > 0)
+  {
+    /* exited process */
+    std::cout << "\tProcess with PID[" << pid 
+              << "] exited with status [" << WEXITSTATUS(status) 
+              << "]" << std::endl;
+  }
+  
+  // check last PID
+  if (pid < 0)              /* error or no childs */
+  {
+    if (errno != ECHILD)
+      std::cerr << "Waitpid error : " << ::strerror(errno) << std::endl;
+    
+    std::cout << "Zombie check has been done. "
+                 "There is no child processes left" << std::endl;
+    return false;
+  }
+  else                      /* no exited processes */
+  {
+    std::cout << "Zombie check has been done. "
+                 "There is still some running child processes." << std::endl;
+    return true;
+  }
+}
+
+
+//////////// WORK
+
+void  some_work()
+{
+  int counter = 0;
+  while (counter < CHILDS_NUMBER)
+  {
+    std::cout << "\n*Doing some hard work*" << std::endl;
+    sleep(WORK_DELAY);
+
+    if (!check_zombies())
+    {
+      std::cout << "\n*Hard work has been done*" << std::endl;
+      return;
+    }
+  }
+}
+
+
+///////////////// MAIN
+
+int   main()
+{
+  create_childs();
+  some_work();
+}