//third.cc

#include <pthread.h>
#include <stdio.h>
#include <sys/types.h>
#include <time.h>
#include <assert.h>
#include <stdlib.h>
#include <math.h>
#include <unistd.h>

// shared memory

int balance = 0;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

// a simple routine for thread execution

void* func(void* which) {
  // lock
  pthread_mutex_lock( &mutex );

  // get old balance
  int oldbalance = balance;
  printf( "This is thread %d. Old balance = %d\n", (int)which, oldbalance );

  // randomly wait 0 to 2 seconds, simulating computation
  srand(time(0)); srand48(time(0));
  int sleep_seconds = (int)( (float)drand48() * 4 );
  sleep( sleep_seconds );

  // increase balance
  balance = oldbalance + 1000;
  printf( "This is thread %d. New balance = %d\n", (int)which, balance );

  // unlock
  pthread_mutex_unlock( &mutex );
}

// main function: generates some threads

int main(int argc, char *argv[])
{
  // get default attributes
  pthread_attr_t attr;
  pthread_attr_init(&attr); 

  // thread creation
  pthread_t tid1, tid2;
  pthread_create(&tid1, &attr, func, (void*)1);
  pthread_create(&tid2, &attr, func, (void*)2);

  // thread join: wait till the threads finish
  pthread_join(tid1, NULL);
  pthread_join(tid2, NULL);
}