Big Threading Problem

[compuKidd]

I need to do merge sort with threading but it seems to take more time with threading rather than no threading , and I have core quad!

please help

#include <iostream>
#include <fstream>
#include <windows.h>
#include <process.h>
#include <conio.h>
#include <time.h>

using namespace std;

int threadCount=0;

HANDLE ghMutex;

class mSortArg
{
public:
	int *a;
	int start;
	int end;
	int threads;

	mSortArg(int *A=NULL,int Start=0,int End=0,int Threads=0)
	{
		a=A;
		start=Start;
		end=End;
		threads=Threads;
	}
};

void merge(int a[],int s1,int e1,int s2,int e2)
{
	int s=(e1-s1+1)+(e2-s2+1);
	int *b=new int [s];
	int i1=s1;
	int i2=s2;
	int i=0;
	while(i1<=e1 && i2<=e2)
	{
		if(a[i1]<a[i2])
		{
			b[i]=a[i1];
			i1++;
		}
		else
		{
			b[i]=a[i2];
			i2++;
		}
		i++;
	}
	for(int j=i1;j<=e1;j++)
	{
		b[i]=a[j];
		i++;
	}
	for(int j=0;j<i;j++)
	{
		a[s1+j]=b[j];
	}
	delete []b;
}

void mergeSortHelp(int[],int,int,int);
unsigned __stdcall threadFunc(void *param)
{
	mSortArg *arg=(mSortArg*)param;

	mergeSortHelp(arg->a,arg->start,arg->end,arg->threads);

	WaitForSingleObject(ghMutex,INFINITE);
	threadCount--; //critical
	ReleaseMutex(ghMutex);
	_endthreadex(0);
	return 0;
}


void mergeSortHelp(int a[],int start,int end,int threads)
{
	if(start>=end)
		return;
	int mid=start+(end-start)/2;
	HANDLE th1=0;

	mSortArg *arg=NULL;
	WaitForSingleObject(ghMutex,INFINITE);
	if(threadCount<threads) // comparison is critical
	{
		threadCount++; //critical
		ReleaseMutex(ghMutex);

		arg=new mSortArg(a,start,mid,threads);
		th1=(HANDLE)_beginthreadex(NULL,0,threadFunc,arg,0,NULL);

	}
	else
	{
		ReleaseMutex(ghMutex);
		mergeSortHelp(a,start,mid,threads);
	}

	mergeSortHelp(a,mid+1,end,threads);
	WaitForSingleObject(th1,INFINITE);
	delete arg;	//shallow delete
	merge(a,start,mid,mid+1,end);
}

void mergeSort(int a[],int size,int threads)
{
	mergeSortHelp(a,0,size-1,threads);
}

int* mergeSort(char *fname,int threads,int &size)
{
	ifstream in(fname);
	in>>size;
	int *a=new int[size];
	for(int i=0;i<size;i++)
	{
		in>>a[i];
	}
	in.close();
	mergeSortHelp(a,0,size-1,threads);
	return a;
}

bool check(int a[],int s)
{
	for(int i=0;i<s-1;i++)
	{
		if(a[i]>a[i+1]) return 0;
	}
	return 1;
}
int main()
{
	ghMutex=CreateMutex(NULL,FALSE,NULL);
	ReleaseMutex(ghMutex); //just in case

	int N=100;

	clock_t t1=clock();
	int a[100]={0};
	for(int i=0;i<1000;i++)
	{
		mergeSort(a,N,0);// zero for no threading, put 1 for using only 1 thread, 2 for two threads ect...
	}
	clock_t t2=clock();
	double t=(t2-t1)/(CLOCKS_PER_SEC*1000.0);

	cerr<<t<<"s\n";
	if(check(a,N)) cerr<<"OK!\n";
	else cerr<<"oooops!!!\n";
}

any help is appreciated