Value a portfolio that doesn't exist. Choose a client (their country decides the currency) and some holdings, and the desk values it live, from the same prices as the real portfolios, recalculating as they move.
Behind it, this page sends the portfolio to the desk as a private task: a worker of its own looks up the client's currency and what each holding is and where it trades, then follows the prices it needs. Its results come back to this page only; nothing is published or shared with other workers. Stop, or leave the page, and the task and its worker are removed.