/*
 * posix_threads.cpp
 *
 *  Created on: 10.01.2011
 *      Author: mk
 */

#include <pthread.h> // POSIX-threads
#include <time.h> // time operations (to calculate the runtime)
#include <stdio.h> // standard IO operations (to print to console)
#include <stdlib.h> // general purpose standard library (to generate random numbers)
#define NUM_ELEMENTS 1000000 // number of array-elements to add

pthread_t* threads; // stores the posix-thread-objects
int* threadNums; // stores the thread-numbers
time_t beginCalc,endCalc; // used to calculate the runtime of the program
unsigned long a[NUM_ELEMENTS],b[NUM_ELEMENTS],c[NUM_ELEMENTS]; // arrays to add (c=a+b)
int numThreads; // number of threads to create

/*
 * fills the arrays with random numbers between 0 and 9
 */
void fillArrays()
{
	for(unsigned i=0;i<NUM_ELEMENTS;i++)
	{
		a[i] = rand() % 10;
		b[i] = rand() % 10;
	}
}

/*
 * this function is called after a thread has been created by pthread_create
 */
void* addArrays(void* pThreadNum)
{
    int* threadNum = (int*)pThreadNum;
    printf("Thread %i started\n",*threadNum);
    unsigned begin,end; // stores the first and last array index which this thread calculates
    if(*threadNum == -1) // only one thread, so no POSIX-threads to create
    {
    	begin = 0;
    	end = NUM_ELEMENTS;
    }
    else // calculate the first and last array index this thread has to calculate
    {
    	begin = (NUM_ELEMENTS/numThreads)**threadNum;
    	end = (NUM_ELEMENTS/numThreads)*(*threadNum+1);
    }
    for (unsigned j=0;j<10000;j++) // run 10.000 times to get a runtime long enough to compare
		for (unsigned i=begin;i<end;i++)
			c[i] = a[i] + b[i]; // add array elements
}

int main(int argc, char* argv[])
{
	if(argc!=2)
	{
		printf("error! first parameter should be: number of threads\n");
		return -1;
	}
	numThreads = atoi(argv[1]); // get number of threads from the first parameter
	fillArrays(); // fill the arrays with random numbers
	time(&beginCalc); // store the time at the beginning of the calculation
	if(numThreads==1) // no POSIX-threads need to be created
	{
		int noThreads = -1;
		addArrays((void*)&noThreads);
	}
	else if(numThreads>1)
	{
		threads = (pthread_t*)malloc(numThreads*sizeof(pthread_t)); // reserve memory for the threads
		threadNums = (int*)malloc(numThreads*sizeof(int)); // reserve memory for the thread-numbers
		for (unsigned i=0;i<numThreads;i++)
		{
			threadNums[i] = i;
			pthread_create(&threads[i],NULL,addArrays,(void *)&threadNums[i]); // create thread
		}
		 // wait for termination of all threads
		for(unsigned i=0;i<numThreads;i++)
			pthread_join(threads[i],NULL);
		// free memory
		free(threads);
		free(threadNums);
	}
	else
	{
		printf("error! number of threads must be positive\n");
		return -1;
	}
	time(&endCalc); // store the time at the end of the calculation
	double timePassed = difftime(endCalc,beginCalc); // calculate the passed time between beginning and end of the calculation
	printf("%f seconds passed\n",timePassed);
	return 0;
}