Handlerdriven

Handlerdriven is a software design approach in which the control flow and behavior of a system are primarily determined by discrete handlers. A handler is a small unit of code that responds to a specific event, message, or request. A central dispatcher or router selects and invokes the appropriate handler at runtime, often using a registry or map of event identifiers to handlers.

Core characteristics include decoupling between event sources and processing logic, modularity through isolated handlers, and extensibility via handler registration or replacement. This approach is common in event-driven architectures, where user actions, I/O events, or messages trigger corresponding handlers, and in frameworks that expose request handlers, callback functions, or middleware chains.

Typical architectures and contexts for handlerdriven systems include graphical user interfaces, web frameworks where each endpoint or route is implemented as a handler, network protocol stacks with protocol or message handlers, and serverless or microservice environments where distinct handlers process individual tasks or events. The pattern supports reuse, testing of handlers in isolation, and easier runtime extensibility by adding or swapping handlers without altering core dispatch logic.

Potential trade-offs involve managing complexity in the dispatcher’s routing logic, ensuring consistent state across multiple handlers, and potential performance overhead from dispatching through layers of handlers. Effective use often relies on clear naming, well-defined handler interfaces, and a robust mechanism for registering, composing, and observing handlers.

See also: event-driven programming, callback, handler pattern, middleware, dispatcher, plugin architecture.