pearson pthread c++

pearson pthread c++

using namespace std;

#include <unistd.h>     /* Symbolic Constants */
#include <sys/types.h>  /* Primitive System Data Types */ 
#include <errno.h>      /* Errors */
#include <stdio.h>      /* Input/Output */
#include <stdlib.h>     /* General Utilities */
#include <pthread.h>    /* POSIX Threads */
#include <string.h>     /* String handling */
#include <iostream>

int flag[2];
int turn;

#define randomdelay usleep(rand()%20)

void *peterson(void * ptr)
{
  int *temp = (int *) ptr;
  int i = *temp;
  cout << "Process " << i << "created" << endl;
  int j = 1-i;

  while(1)
    {
      // Non-critical section
      // We do not really care what happens here. But we care that it may take different times. Hence, will invoke a random number generator for doing wait
      
      randomdelay;
      flag[i] = 1;
      // There is a possibility that the thread may get swapped out here. So, add a random delay
      randomdelay;
      turn = j;
      randomdelay;
      while(flag[j]==1 && turn==j);
      // Entering CS
      cout << "Entering CS process " << i << endl;
      sleep(10);
      cout << "Exiting CS process " << i << endl;
    }
}

int main()
{
  flag[0] = 0;
  flag[1] = 0;
  turn = 0; // Not needed since turn is never used without being set first
     
  pthread_t thread1, thread2;  /* thread variables */
  int p0 = 0;
  int p1 = 1;

  pthread_create(&thread1, NULL,  peterson, (void *) &p0);
  pthread_create(&thread2, NULL,   peterson, (void *) &p1);


  pthread_join(thread1, NULL);
  pthread_join(thread2, NULL);
              
  /* exit */  
  exit(0);
}