A reactor allows multiple tasks which block (say due to IO) to be processed efficiently using a single thread. The reactor manages a pool of handlers and runs an event loop. When it is called to perform a task it links it with a new or vacant handler making it active. The event loop (1) finds all the handlers that are active and unblocked (or delegates this to a dispatcher implementation) (2) executes each of these found handlers sequentially until they either complete or reach a point where they block. Completed handlers become inactive and vacant for reuse whereas blocked active handlers yield, allowing the event loop to continue. (3) Repeats from step (1)
