extern "C" {
#include <errno.h>
#include <memory.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sched.h>
#include <sys/wait.h>
#include <sys/shm.h>
#include <sys/resource.h>
#include <sys/mman.h>
}

extern "C"
void child_signal_handler(
   const int
)
{
   int   errno_save;
   pid_t dead_pid;
   int   dead_status;

   errno_save = errno;

   do {
      dead_pid = waitpid(-1, &dead_status, WNOHANG);
      if (dead_pid == -1) {
         if (errno == ECHILD) break;
         perror("waitpid");
         exit(1);
      }
   } while (dead_pid != 0);

   errno = errno_save;

   return;
}

int rabbits(void)
{
   int pid = fork();
   if (pid != 0) {

      return 0;

   } else {

      const int sched_policy = sched_getscheduler(0);
      if (sched_policy == -1) {
         perror("sched_getscheduler");
      }
      if (sched_policy != SCHED_OTHER) {
         sched_param sched;
         memset(&sched, 0, sizeof(sched));
         sched.sched_priority = 0;
         if (sched_setscheduler(0, SCHED_OTHER, &sched) != 0) {
            perror("sched_setscheduler");
         }
      }
      errno = 0;                   // -1 return value legitimate
      const int nice = getpriority(PRIO_PROCESS, 0);
      if (errno != 0) {
         perror("getpriority");
      }
      if (nice < -10) {
         if (setpriority(PRIO_PROCESS, 0, -10) != 0) {   // somewhat elevated
            perror("setpriority");
         }
      }

      char* program;
      program = (char*) "script";
      char* pargs[2];
      pargs[0] = program;
      pargs[1] = NULL;
      execvp(program, pargs);
      perror("execvp");
      exit(1);

   }

}

int main(
   int          argc,
   const char** argv,
   const char** envp
)
{
#if 1
   sched_param sched;
   memset(&sched, 0, sizeof(sched));
   sched.sched_priority = 26;
   if (sched_setscheduler(0, SCHED_RR, &sched) != 0) {
      perror("sched_setscheduler(SCHED_RR, 26)");
      return 1;
   }
#endif

#if 0
   if (mlockall(MCL_CURRENT|MCL_FUTURE) != 0) {
      perror("mlockall");
      return 1;
   }
#endif

   struct sigaction sas_child;
   memset(&sas_child, 0, sizeof(sas_child));
   sas_child.sa_handler = child_signal_handler;
   if (sigaction(SIGCHLD, &sas_child, NULL) != 0) {
      perror("sigaction(SIGCHLD)");
      return 1;
   }

   int seg1id = shmget(0x12345600,
                       (size_t) 0xC0000000,
                       IPC_CREAT|SHM_HUGETLB|0640
                      );
   if (seg1id == -1) {
      perror("shmget(3GB)");
      return 1;
   }
   void* seg1adr = shmat(seg1id, (void*) 0x400000000, 0);
   if (seg1adr == (void*) -1) {
      perror("shmat(3GB)");
      return 1;
   }
#if 1
   memset(seg1adr, 0xFF, (size_t) 0x60000000);
   if (mlock(seg1adr, (size_t) 0xC0000000) != 0) {
      perror("mlock(3GB)");
      return 1;
   }
#endif

   int seg2id = shmget(0x12345601,
                       (size_t) 0x40000000,
                       IPC_CREAT|SHM_HUGETLB|0640
                      );
   if (seg2id == -1) {
      perror("shmget(1GB)");
      return 1;
   }
   void* seg2adr = shmat(seg2id, (void*) 0x500000000, 0);
   if (seg2adr == (void*) -1) {
      perror("shmat(1GB)");
      return 1;
   }
#if 1
   memset(seg2adr, 0xFF, (size_t) 0x40000000);
   if (mlock(seg2adr, (size_t) 0x40000000) != 0) {
      perror("mlock(1GB)");
      return 1;
   }
#endif

   for (int i1 = 0; i1 < 50; i1++) {
      void* mmtarg = mmap(NULL,
                          528384,
                          PROT_READ|PROT_WRITE,
                          MAP_PRIVATE|MAP_ANONYMOUS,
                          -1,
                          0
                         );
      if (mmtarg == (void*) -1) {
         perror("mmap");
         return 1;
      }
   }

   for (int i1 = 0; i1 < 50; i1++) {
      rabbits();
      usleep(500);
   }

   while (true) {
      pause();
   }

   return 0;
}