#include <windows.h>
#include <cstdlib>
#include <random>
#include <iostream>

using namespace std;

size_t const BLOCK_SIZE = 4096;
size_t const NUM_BLOCKS = ((size_t)1024 * 1024 * 1024 / BLOCK_SIZE);
size_t const FILE_SIZE  = NUM_BLOCKS * BLOCK_SIZE;

int main()
{
    unsigned const PARALLEL_DEGREE = 500;
    HANDLE         hFile;
    OVERLAPPED     aol[PARALLEL_DEGREE];
    BYTE           abBlock[BLOCK_SIZE];
    HANDLE         hIoCompletionPort;

    if( (hFile = CreateFile( TEXT("testfile"), GENERIC_READ | GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_FLAG_NO_BUFFERING | FILE_FLAG_OVERLAPPED, NULL )) == INVALID_HANDLE_VALUE )
        return EXIT_FAILURE;

    aol[0].Offset = FILE_SIZE - BLOCK_SIZE;
    aol[0].OffsetHigh = 0;
    if( (aol[0].hEvent = CreateEvent( NULL, FALSE, FALSE, NULL )) == NULL ||
        !WriteFile( hFile, abBlock, FILE_SIZE - BLOCK_SIZE, NULL, &aol[0] ) && GetLastError() != ERROR_IO_PENDING )
        return EXIT_FAILURE;

    if( (hIoCompletionPort = CreateIoCompletionPort( hFile, NULL, NULL, 1 )) == NULL )
        return EXIT_FAILURE;

    random_device                   rd;
    mt19937                         mt( rd() );
    uniform_int_distribution<DWORD> uid( 0, FILE_SIZE - BLOCK_SIZE );

    for( unsigned par = 0; par < PARALLEL_DEGREE; par++ )
    {
        aol[par].Offset     = uid( mt ) & (DWORD)-(LONG)BLOCK_SIZE;
        aol[par].OffsetHigh = 0;
        aol[par].hEvent     = NULL;
        if( !ReadFile( hFile, abBlock, BLOCK_SIZE, NULL, &aol[par] ) && GetLastError() != ERROR_IO_PENDING )
            return EXIT_FAILURE;
    }

    for( ; ; )
    {
        DWORD       dwBytesTransferred;
        ULONG_PTR   ulpKey;
        OVERLAPPED *pol;

        if( !GetQueuedCompletionStatus( hIoCompletionPort, &dwBytesTransferred, &ulpKey, &pol, INFINITE ) )
            return EXIT_FAILURE;

        pol->Offset     = uid( mt ) & (DWORD)-(LONG)BLOCK_SIZE;
        pol->OffsetHigh = 0;
        pol->hEvent     = NULL;
        if( !ReadFile( hFile, abBlock, BLOCK_SIZE, NULL, pol ) && GetLastError() != ERROR_IO_PENDING )
            return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}