Нити в winapi

#include <Windows.h>
#include <stdio.h>
#include <conio.h>
 
#define DWORD_CAST(High, Low) (((unsigned long long)High << 32) + (DWORD)Low)
#define HIGH_DWORD(value) (DWORD)((unsigned long long)value >> 32)
 
#define BUFFER_SIZE 0x10000
 
void main()
{
    char sInput[MAX_PATH] = { 0 };
    char sOutput[MAX_PATH] = { 0 };
    HANDLE hInput = NULL;
    HANDLE hOutput = NULL;
    HANDLE hEvent = NULL;
    OVERLAPPED stReader = { 0 };
    OVERLAPPED stWriter = { 0 };
    BYTE pBuffer[BUFFER_SIZE] = { 0 };
    DWORD nFileSizeLow = 0;
    DWORD nFileSizeHigh = 0;
    DWORD nFileSize = 0;
    DWORD nBlockSize = 0;
    DWORD nOffset = 0;
    DWORD nBytesWrite = 0;
    DWORD nBytesRead = 0;
    long long reader_offset = 0;
    long long writer_offset = 0;
 
    //Открытие копируемого файла
    printf("Input filename: ");
    gets(sInput);
    hInput = CreateFileA(sInput, GENERIC_READ, 0, NULL, OPEN_EXISTING, FILE_FLAG_OVERLAPPED|FILE_FLAG_NO_BUFFERING, NULL);
    if (hInput == INVALID_HANDLE_VALUE)
    {
        printf("\nError: %d", GetLastError());
        goto final;
    }
 
    //Открытие выходного файла
    printf("Output filename: ");
    gets(sOutput);
    hOutput = CreateFileA(sOutput, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_FLAG_OVERLAPPED|FILE_FLAG_NO_BUFFERING, NULL);
    if (hOutput == INVALID_HANDLE_VALUE)
    {
        printf("\nError: %d", GetLastError());
        goto final;
    }
 
    //Создание нити
    hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
    stReader.hEvent = hEvent;
    stWriter.hEvent = hEvent;
 
    //Получение размера файла
    nFileSizeLow = GetFileSize(hInput, &nFileSizeHigh);
    nFileSize = DWORD_CAST(nFileSizeHigh, nFileSizeLow);
    nBlockSize = nFileSize < BUFFER_SIZE ? nFileSize : BUFFER_SIZE;
 
    //Читать данные из входного в файла и запись в выходной пока смещение меньше размера файла
    while ((nOffset = DWORD_CAST(stReader.OffsetHigh, stReader.Offset)) < nFileSize)
    {
        ResetEvent(stReader.hEvent);
        nBlockSize = nOffset > BUFFER_SIZE ? BUFFER_SIZE : nFileSize - reader_offset;
 
        ReadFile(hInput, pBuffer, nBlockSize, NULL, &stReader);
        WriteFile(hOutput, pBuffer, nBlockSize, NULL, &stWriter);
        WaitForSingleObject(hEvent, INFINITE);
 
        GetOverlappedResult(hOutput, &stWriter, &nBytesWrite, FALSE);
        writer_offset += nBytesWrite;
        stWriter.Offset = (DWORD)writer_offset;
        stWriter.OffsetHigh = HIGH_DWORD(writer_offset);
 
        GetOverlappedResult(hInput, &stReader, &nBytesRead, FALSE);
        reader_offset += nBytesRead;
        stReader.Offset = (DWORD)reader_offset;
        stReader.OffsetHigh = HIGH_DWORD(reader_offset);
 
        memset(pBuffer, 0, BUFFER_SIZE);
    }
 
final:
    CloseHandle(hInput);
    CloseHandle(hOutput);
    getch();
}