Supervisor Program Forking to a Multi-threaded Child - c++

Question

First off, allow me to describe my scenario:
I developed a supervisory program on Linux that forks and then uses execv(), in the child process, to launch my multi-threaded application. The supervisory program is acting as a watchdog to the multi-threaded application. If the multi-threaded application does not send a SIGUSR1 signal to the supervisor after a period of time then the supervisory program will kill the child using the pid_t from the fork() call and repeat the process again.
Here is the code for the Supervisory Program:
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <iostream>
#include <cerrno>
time_t heartbeatTime;
void signalHandler(int sigNum)
{
//std::cout << "Signal (" << sigNum << ") received.\n";
time(&heartbeatTime);
}
int main(int argc, char *argv[])
{
pid_t cpid, ppid;
int result = 0;
bool programLaunched = false;
time_t now;
double timeDiff;
int error;
char ParentID[25];
char *myArgv[2];
// Get the Parent Process ID
ppid = ::getpid();
// Initialize the Child Process ID
cpid = 0;
// Copy the PID into the char array
sprintf(ParentID, "%i", ppid);
// Set up the array to pass to the Program
myArgv[0] = ParentID;
myArgv[1] = 0;
// Print out of the P PID
std::cout << "Parent ID: " << myArgv[0] << "\n";
// Register for the SIGUSR1 signal
signal(SIGUSR1, signalHandler);
// Register the SIGCHLD so the children processes exit fully
signal(SIGCHLD, SIG_IGN);
// Initialize the Heart Beat time
time(&heartbeatTime);
// Loop forever and ever, amen.
while (1)
{
// Check to see if the program has been launched
if (programLaunched == false)
{
std::cout << "Forking the process\n";
// Fork the process to launch the application
cpid = fork();
std::cout << "Child PID: " << cpid << "\n";
}
// Check if the fork was successful
if (cpid < 0)
{
std::cout << "Error in forking.\n";
// Error in forking
programLaunched = false;
}
else if (cpid == 0)
{
// Check if we need to launch the application
if (programLaunched == false)
{
// Send a message to the output
std::cout << "Launching Application...\n";
// Launch the Application
result = execv("./MyApp", myArgv);
std::cout << "execv result = " << result << "\n";
// Check if the program launched has failed
if (result != -1)
{
// Indicate the program has been launched
programLaunched = true;
// Exit the child process
return 0;
}
else
{
std::cout << "Child process terminated; bad execv\n";
// Flag that the program has not been launched
programLaunched = false;
// Exit the child process
return -1;
}
}
}
// In the Parent Process
else
{
// Get the current time
time(&now);
// Get the time difference between the program heartbeat time and current time
timeDiff = difftime(now, heartbeatTime);
// Check if we need to restart our application
if ((timeDiff > 60) && (programLaunched == true))
{
std::cout << "Killing the application\n";
// Kill the child process
kill(cpid, SIGINT);
// Indicate that the process was ended
programLaunched = false;
// Reset the Heart Beat time
time(&heartbeatTime);
return -1;
}
// Check to see if the child application is running
if (kill(cpid, 0) == -1)
{
// Get the Error
error = errno;
// Check if the process is running
if (error == ESRCH)
{
std::cout << "Process is not running; start it.\n";
// Process is not running.
programLaunched = false;
return -1;
}
}
else
{
// Child process is running
programLaunched = true;
}
}
// Give the process some time off.
sleep(5);
}
return 0;
}
This approach worked fairly well until I ran into a problem with the library I was using. It didn't like all of the killing and it basically ended up tying up my Ethernet port in an endless loop of never releasing - not good.
I then tried an alternative method. I modified the supervisory program to allow it to exit if it had to kill the multi-threaded application and I created a script that will launch the supervisor program from crontab. I used a shell script that I found on Stackoverflow.
#!/bin/bash
#make-run.sh
#make sure a process is always running.
export DISPLAY=:0 #needed if you are running a simple gui app.
process=YourProcessName
makerun="/usr/bin/program"
if ps ax | grep -v grep | grep $process > /dev/null
then
exit
else
$makerun &
fi
exit
I added it to crontab to run every minute. That was very helpful and it restarted the supervisory program which in turn restarted multi-threaded application but I noticed a problem of multiple instances of the multi-threaded application being launched. I'm not really sure why this was happening.
I know I'm really hacking this up but I'm backed into a corner with this implementation. I'm just trying to get it to work.
Suggestions?