#include <iostream>
#include <windows.h>
#include <iomanip>

using namespace std;

HANDLE* threads;
HANDLE* events;
const int N = 10000000;
const int blockSize = 70000;
const int maxBlocks = N / blockSize + 1;
volatile double pi = 0;
volatile long int blockNum;

DWORD WINAPI func(LPVOID lpParameter)
{
	double _pi = 0;
	int num = (int)lpParameter;
	while (true)
	{
		int start = num * blockSize;
		int end = (num + 1)*blockSize;
		if (end > N)
			end = N;
		for (size_t i = start; i < end; i++)
		{
			_pi += 4 / (1 + pow((i + 0.5) / N, 2));
		}
		//cout << "thread finished countin (" << start << ": " << end << ") blocknum is " << blockNum << endl;
		SetEvent(events[(int)lpParameter]);
		num = InterlockedExchangeAdd(&blockNum, 1);
		if (blockNum > maxBlocks)
			break;
		SuspendThread(threads[(int)lpParameter]);
	}
	//cout << "finish" << endl;
	pi += _pi;
	return 0;
}

int main()
{
	int maxThreads;
	int freeThread = NULL;

	cout << "Threads amount: ";
	cin >> maxThreads;

	threads = new HANDLE[maxThreads];
	events = new HANDLE[maxThreads];

	for (size_t i = 0; i < maxThreads; i++)
	{
		threads[i] = CreateThread(NULL, 0, func, (void*)i, CREATE_SUSPENDED, NULL);
		events[i] = CreateEventA(NULL, true, true, NULL);
	}
	blockNum = maxThreads;

	double start = GetTickCount();

	while (blockNum < maxBlocks)
	{
		freeThread = WaitForMultipleObjects(maxThreads, events, false, INFINITE) - WAIT_OBJECT_0;
		//cout << "free thread " << freeThread << "(blockNum is " << blockNum << ")" << endl;
		ResumeThread(threads[freeThread]);
		ResetEvent(events[freeThread]);
	}
	for (size_t i = 0; i < maxThreads; i++)
	{
		ResumeThread(threads[i]);
	}
	WaitForMultipleObjects(maxThreads, threads, true, INFINITE);
	pi = pi / N;

	double end = GetTickCount();

	cout << setprecision(75) << pi << endl;
	cout << "time: " << end - start << " ms" << endl;

	/*for (size_t i = 0; i < maxThreads; i++)
	{
		CloseHandle(threads[i]);
		CloseHandle(events[i]);
	}*/
	system("pause");
	return 0;
}