Reactorstyle

Reactorstyle, often referred to as the Reactor pattern, is an architectural approach used to build event-driven, high-concurrency applications, especially network servers. The central idea is to use a single or small number of event loops to monitor multiple I/O sources through non-blocking operations and readiness notifications, and to dispatch ready events to registered handlers for processing.

In a typical reactor-style system, the event loop registers channels or sockets with an I/O multiplexing mechanism (such as epoll, kqueue, or IOCP) and associates each with a handler. When the operating system indicates that a source is ready, the reactor invokes the corresponding handler. Handlers perform short, non-blocking work and may delegate longer tasks to worker pools or separate threads to keep the event loop responsive. This separation helps maintain scalability as load increases.

There are variations in how reactors are deployed. Some designs use a single-threaded reactor handling all events, while others employ multiple reactors coordinating with thread pools or partitioned workloads to improve parallelism. Reactor-style systems are commonly contrasted with proactor-style designs, where the initiation of I/O and the completion of asynchronous operations are managed differently; reactor-style emphasizes readiness demultiplexing and dispatching in response to OS signals.

Use cases for reactor-style architectures include high‑throughput network servers, real-time messaging, and other I/O-bound applications that require scalable event handling without blocking operations. The term appears in both academic discussions and practical framework implementations, where it is associated with event loops, non-blocking I/O, and efficient task dispatching.

See also: event-driven programming, non-blocking I/O, I/O multiplexing, Proactor pattern, Netty, libuv.