Reactor Pattern

1. Introduction

The Reactor Pattern is a design pattern that enables event-driven programming. It allows an application to handle asynchronous events, making it particularly useful in networking and GUI applications where multiple events can occur simultaneously.

2. Key Concepts

• Event Handling: The Reactor Pattern is centered around event handling and callback functions.
• Event Loop: The pattern typically includes an event loop that waits for events to occur and dispatches them to appropriate handlers.
• Demultiplexer: A demultiplexer is used to listen to multiple sources of events and delegate them to the appropriate handlers.

3. Implementation

Here is a simple implementation of the Reactor Pattern using Python:

import select
import socket

class Reactor:
    def __init__(self):
        self.inputs = []
        self.outputs = []

    def register_input(self, sock):
        self.inputs.append(sock)

    def register_output(self, sock):
        self.outputs.append(sock)

    def run(self):
        while True:
            readable, writable, exceptional = select.select(self.inputs, self.outputs, [])
            for s in readable:
                data = s.recv(1024)
                if data:
                    self.handle_event(data)

    def handle_event(self, data):
        print("Received:", data)

# Example Usage
server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server.bind(('localhost', 12345))
server.listen(5)

reactor = Reactor()
reactor.register_input(server)
reactor.run()

4. Best Practices

• Use Non-blocking I/O: Ensure your event handlers are non-blocking to prevent delays in event processing.
• Keep Handlers Lightweight: Minimize the work done in event handlers to keep the event loop responsive.
• Manage Resources: Properly manage resources to avoid memory leaks, especially when working with sockets.

5. FAQ