 Event loop

An event loop repeatedly obtains pending software events and dispatches them to their event handlers, waiting when no work is available. This lets one thread service many intermittent activities without a separate continuously running loop for each. Qt's application event loop dispatches timer, network and other software events.^[ref]

Suppose a button starts a calculation that takes ten seconds. Running that calculation synchronously inside its event handler prevents the same event loop from repainting or processing further clicks during those ten seconds. Dividing the work into short steps or delegating it to another thread lets the event handler return. An event loop coordinates readiness and dispatch; it does not itself provide parallel computing for long computations.