Src for a win32 console program that demonstrates cross-thread shared file access.

InProcessThreadShareTest.cpp

// InProcessThreadShareTest.cpp : Defines the entry point for the console application.
//

#include "stdafx.h" 
#include <windows.h> 

void EmitError(DWORD dwErr) 
{
	if(dwErr != 0) 
	{
		LPVOID tszBuf = 0;
		DWORD dwFmt = FormatMessage(
			FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
			0, dwErr, 0, (LPTSTR)(&tszBuf), 0, 0);
		_tprintf(_T("Message:\r\n--\r\n%s\t\n"), (LPTSTR)tszBuf); 
		if(tszBuf){::LocalFree(&tszBuf);} 
	}
}

DWORD WINAPI OtherThreadProc(LPVOID arg)
{
	_tprintf(_T("** Begin Other Thread\r\n")); 
	HANDLE hFile = ::CreateFile(_T("C:\\data\\tmp\\sharetest.txt"), 
		(GENERIC_READ | GENERIC_WRITE), 
		(FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE),
		0, OPEN_EXISTING, 
		FILE_ATTRIBUTE_NORMAL | FILE_ATTRIBUTE_TEMPORARY | FILE_FLAG_DELETE_ON_CLOSE, 
		0);
	DWORD dwErr = GetLastError();
	_tprintf(_T("File Handle: %8.8x\r\n"), (ULONG)hFile); 
	_tprintf(_T("Last Error: %8.8x\r\n"), dwErr); 
	if(dwErr != 0) 
	{
		EmitError(dwErr);
	}
	else 
	{
		DWORD dwIn = 0;
		DWORD dwData = 0;
		_tprintf(_T("Old Data: %8.8x\r\n"), dwData); 
		::ReadFile(hFile, &dwData, sizeof(DWORD), &dwIn, 0); 
		_tprintf(_T("New Data: %8.8x\r\n%d bytes read.\r\n"), dwData, dwIn); 
		DWORD dwPos = sizeof(DWORD); 
		DWORD dwOut = 0;
		dwData = 0xF0F0F0F0;
		::SetFilePointer(hFile, dwPos, 0, FILE_BEGIN);
		::WriteFile(hFile, &dwData, sizeof(DWORD), &dwOut, 0); 
		::FlushFileBuffers(hFile);
		_tprintf(_T("Wrote New Data: %8.8x @ 0x%8.8x\r\n"), dwData, dwPos); 
		_tprintf(_T("New Size: %d bytes\r\n"), GetFileSize(hFile, NULL)); 
	}
	Sleep(4000);
	::CloseHandle(hFile);
	_tprintf(_T("** End Other Thread\r\n")); 
	return 0; 
}

int _tmain(int argc, _TCHAR* argv[]) 
{
	_tprintf(_T("** Begin Main Thread\r\n")); 
	_tprintf(_T("Creating File\r\n")); 
	HANDLE hFile = ::CreateFile(_T("C:\\data\\tmp\\sharetest.txt"), 
		(GENERIC_READ | GENERIC_WRITE), 
		(FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE),
		0, CREATE_ALWAYS, 
		FILE_ATTRIBUTE_NORMAL | FILE_ATTRIBUTE_TEMPORARY | FILE_FLAG_DELETE_ON_CLOSE, 
		0);

	DWORD dwErr = GetLastError();
	if(dwErr != 0) 
	{
		EmitError(dwErr);
		_tprintf(_T("** Exit Main Thread\r\n")); 
		Sleep(20000);
		return 1; 
	}
	DWORD dwData = 0x12345678;
	DWORD dwOut = 0;
	::WriteFile(hFile, &dwData, sizeof(DWORD), &dwOut, 0); 
	_tprintf(_T("Wrote New Data: %8.8x (%d bytes)\r\n"), dwData, dwOut); 
	::FlushFileBuffers(hFile);
	_tprintf(_T("New Size: %d bytes\r\n"), GetFileSize(hFile, NULL)); 

	DWORD threadID = 0;
	HANDLE hThread = ::CreateThread(0, 0, OtherThreadProc, 0, 0, &threadID);
	_tprintf(_T("** Sleep() Main Thread\r\n")); 

	Sleep(10000);

	::CloseHandle(hThread);

	_tprintf(_T("** Resume Main Thread\r\n")); 
	_tprintf(_T("Reported File Size: %d bytes\r\n"), GetFileSize(hFile, NULL)); 
	DWORD dwPos = sizeof(DWORD); 
	DWORD dwIn = 0;
	_tprintf(_T("Old Data: %8.8x\r\nReading from 0x%8.8x\r\n"), dwData, dwPos); 
	dwData = 0;
	::SetFilePointer(hFile, dwPos, 0, FILE_BEGIN);
	dwErr = GetLastError();
	if(dwErr != 0) 
	{
		_tprintf(_T("Error during SetFilePointer()\r\n")); 
		EmitError(dwErr);
	}

	::ReadFile(hFile, &dwData, sizeof(DWORD), &dwIn, 0); 

	dwErr = GetLastError();
	if(dwErr != 0) 
	{
		_tprintf(_T("Error during ReadFile()\r\n")); 
		EmitError(dwErr);
	}
	else 
	{
		_tprintf(_T("New Data: %8.8x\r\n%d bytes read.\r\n"), dwData, dwIn); 
	}

	::CloseHandle(hFile);

	_tprintf(_T("** End Main Thread\r\n")); 
	Sleep(10000);
	return 0; 
}