//created by Dr. Ramsey on 10/25/13
//edits by Dr. Ramsey on 4/18/15

#include <semaphore.h>
#include <fcntl.h> //needed for O_CREAT
#include <iostream>
using namespace std;



int main() {

  int current_value;
  char *name ="rams"; // this is the 'name' of my semaphore

  //open a named semaphore and create if it wasn't created
  //0644 describes the permissions
  //1 is the initial value of the semaphore
  sem_t *sem = sem_open(name, O_CREAT, 0644, 1);

  sem_getvalue(sem, &current_value);
  cout << "Before Entry: The current value of the semaphore is: " << current_value << endl;

  while(sem_wait(sem)); //the usual wait until we can subtract 1 - blocking system call

  sem_getvalue(sem, &current_value);
  cout << "Inside C.S: The current value of the semaphore is: " << current_value << endl;

  cout << "Inside the critical section doing things" << endl;


  //try wait will not block but report an error
  int getlock = sem_trywait(sem);
  if(getlock) { //then some error was reported
    cout << "Error reported from sem_trywait: " << getlock << endl;
  }


  sem_post(sem); //the usual add 1 


  sem_getvalue(sem, &current_value);
  cout << "After Exit: The current value of the semaphore is: " << current_value << endl;


  cout << "Input an integer to continue: ";
  cin >> current_value; //stop the program for demo purposes

  sem_close(sem); //disconnect this process from the semaphore
  //get rid of this semaphore
  sem_unlink(name); //will destroy if all are closed




}