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


#define TIMER_CLEAR     (tv1.tv_sec = tv1.tv_usec = tv2.tv_sec = tv2.tv_usec = 0)
#define TIMER_START     gettimeofday(&tv1, (struct timezone*)0)
#define TIMER_ELAPSED   (double) (tv2.tv_usec-tv1.tv_usec)/1000000.0+(tv2.tv_sec-tv1.tv_sec)
#define TIMER_STOP      gettimeofday(&tv2, (struct timezone*)0)
struct timeval tv1,tv2;
  
pthread_mutex_t myMutex;

#define MAX_THREADS 16

__thread double areaThread, areaThreadTotal;
__thread double myVal;

int NUM_THREADS;
double iterations;
int a = 0, b = 1;
double area, h;
double sumOfRectangles;

// returns square root 
double func(double num)
{
    return sqrt(1-pow(num,2));
}

void *protectedThreadFunc(void* argument)
{
	int i;
	int myId = (int)argument;
	TIMER_START;
	for(i=0;i<=iterations-1;i++)
	{
		areaThread=h*func(a+(i-1)*h);
		areaThreadTotal+=areaThread;
	}
	
	pthread_mutex_lock (&myMutex);
	sumOfRectangles=4*areaThreadTotal;
	TIMER_STOP;
	pthread_mutex_unlock (&myMutex);
	
}

int main(int argc, char * argv[]) 
{
	TIMER_CLEAR;
	if (argc < 3)
	{
		printf("Please specify the iterations or threads\n");
		return -1;
	}
	area = 0;
	int i;
	
	iterations = atoi(argv[1]); // in other words this is n

	NUM_THREADS = atoi(argv[2]);

	h = (b-a)/iterations;
	
	//creating pthread array 
	pthread_t myThreads[NUM_THREADS]; 
	int status = 0;
	

	//printf("Calling protected set of threads\n");
	pthread_mutex_init(&myMutex, NULL);
	//next set of threads will call a function that will update the variable protected 
	for(i=0;i<NUM_THREADS;i++) 
	{
		status = pthread_create(&myThreads[i],NULL,protectedThreadFunc, (void*)i); 
		if(status)
		{
			printf("Error in creating the threads: %d\n",i);
			return -1;
		}
	}
 
	for(i=0;i<NUM_THREADS;i++) 
	{ 
		int retStatus = pthread_join(myThreads[i],NULL); 
		if(retStatus) 
		{ 
			printf("Well..... some problem at thread id %d, error no: %d\n",i,retStatus); 
		} 
	} 
	pthread_mutex_destroy(&myMutex);
	printf("Computed Sum for Rectangular Decomposition: %f\n", sumOfRectangles);
	printf("Time elapsed = %f seconds\n", TIMER_ELAPSED);
	return 0; 
}