// open file for reading and writing
FileStream fs(filepath, std::ios::in | std::ios::out | std::ios::binary);
// write some information
Poco::Int32 i32 = 0;
fs.seekp(0, std::ios::beg);
fs.write((const char *)&i32, sizeof(i32));
fs.flushToDisk();
//...
// other process-reader
FileStreamRWLock fLock(fs, 0, sizeof(Poco::Int32));
ScopedFStreamReadRWLock readLock(fLock);
fs.seekg(0, std::ios::beg);
fs.read((char *)&counter, sizeof(counter));

//...
// other process-writer
FileStreamRWLock fLock(fs, 0, sizeof(Poco::Int32));
ScopedFStreamWriteRWLock writeLock(fLock);
fs.seekp(0, std::ios::beg);
fs.write((char *)&counter, sizeof(counter));
fs.flushToDisk();

HANDLE openFileWithRWAccess(const std::string& path)
{
	DWORD access = GENERIC_READ | GENERIC_WRITE;
	DWORD shareMode = FILE_SHARE_READ | FILE_SHARE_WRITE;

	HANDLE handle = CreateFileA(path.c_str(), access, shareMode, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);

	if (handle == INVALID_HANDLE_VALUE)
		Poco::File::handleLastError(path);

	return handle;
}

FileStream fs;
fs.openHandle(openFileForSahredRWAccess(fl), std::ios::in | std::ios::out | std::ios::binary);