What is the Reactor Pattern?
The Reactor Pattern is a design pattern often used in event-driven programming, especially for scalable network applications. Its main job is to handle multiple service requests that are delivered concurrently to a service handler by one or more input sources (such as network sockets or file descriptors).
How Does It Work in Node.js?
- Event Loop: Node.js uses a single-threaded event loop based on the Reactor Pattern. All incoming requests are registered as events and placed into a queue.
- Event Demultiplexer: The event loop continuously checks this queue, waiting for new events (like network requests, timers, or I/O operations).
- Event Handlers: When an event is detected, Node.js triggers the corresponding callback (event handler), letting your code process it asynchronously, without blocking the main thread.
Key Benefits
- Concurrency Handling: Node.js can handle thousands of simultaneous connections efficiently.
- Non-blocking I/O: Heavy I/O operations (like database or API calls) don't block the execution of other code.
- Scalability: Highly suited for real-time applications (e.g., chat servers, streaming services).
Example: Simple Server using Reactor Pattern
Here's a basic example of Node.js HTTP server:
const http = require('http');
const server = http.createServer((req, res) => {
res.end('Hello, World!');
});
server.listen(3000);
- When an HTTP request comes in, it's handled as an event.
- The server automatically registers the event and invokes the appropriate handler (the function you pass to
createServer).
Summary
The Reactor Pattern is the core reason Node.js is fast and scalable for I/O-heavy applications. It enables asynchronous programming and efficient resource usage using an event-driven, non-blocking architecture.
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