Programming

void PingFunc()
{
  while (1)
  {
  		PingMachine();		
		sleep(15);
   }
}

main()
{
 pthread_t thId;
 pthread_create (&thId, NULL, PingFunc,NULL);
 while(1)
 {
     getrequest();
     processrequest();  
  }
}

1) When there is an explicit call to pthread_exit()

2) When the execution reaches the end curly braces; i.e. the handler function has been executed and/or returns.

3) When the main() terminates; results in the clean up of all the program stack and memory recovery by the OS; lets get the pthread stack cleaned up.

1) You haven't handled any signal/interrupts; so don't expect it to run for years. In other words, its a no robust code. Hence, the moment main()
 is gone, your thread would go.

2) main() is in the busy wait; most of the OS kernel scheduler would detect this easily and (untill explictly elevated in terms of priority) would run off with a low priority in scheduling 
--happens in Linux (trick to overcome in busy wait is to put a few miliseconds of sleep  --but can't generalize this for other OS). 
Instead why don't you just blocked wait in pthread_join() and do that function call in another seperate pthread?