AsyncIO Event Emitter

🏗️ Work in Progress

This page is a work in progress.

  Now that we've covered the base EventEmitter interface, let's examine one of its official implementations: the AsyncIOEventEmitter.

What is it?

  The AsyncIOEventEmitter is a class that inherits from EventEmitter and uses the AsyncIO framework to handle the execution of event emissions.

How it works

  The AsyncIOEventEmitter handles the event emission differently depending on whether it is operating in a synchronous or asynchronous execution context. In synchronous contexts, it will automatically start an event loop to run handlers concurrently. In asynchronous contexts, it leverages any existing event loop. Let's explore the AsyncIOEventEmitter's behavior in more detail:

Sync context

  When running without an existing AsyncIO event loop, the AsyncIOEventEmitter automatically starts a new loop using asyncio.run(). Within this loop, it executes the event emission. The loop then waits for all scheduled tasks to finish before closing. This preserves synchronous execution while still gaining the benefits of the concurrent execution.

Async context

  In an asynchronous context where an event loop is already running, the event emission is scheduled and processed on that existing loop.

AsyncIO Event Loop Behavior

If the event loop is closed before all callbacks complete, any remaining scheduled tasks will be canceled.

Usage

  Using the AsyncIOEventEmitter is straightforward. To get started, simply create a new instance of the class and call its emit() methods, as shown below:

Sync contextAsync context

from pyventus import EventLinker, EventEmitter, AsyncIOEventEmitter


@EventLinker.on("StringEvent")
def sync_event_callback():
    print("Sync event callback!")


@EventLinker.on("StringEvent")
async def async_event_callback():
    print("Async event callback!")


def main():
    event_emitter: EventEmitter = AsyncIOEventEmitter()
    event_emitter.emit("StringEvent")


main()

import asyncio
from pyventus import EventLinker, EventEmitter, AsyncIOEventEmitter

@EventLinker.on("StringEvent")
def sync_event_callback():
    print("Sync event callback!")


@EventLinker.on("StringEvent")
async def async_event_callback():
    print("Async event callback!")


async def main():
    event_emitter: EventEmitter = AsyncIOEventEmitter()
    event_emitter.emit("StringEvent")
    await asyncio.sleep(0.5) # (1)!

asyncio.run(main())

1. By awaiting the asyncio.sleep(0.5), we ensure the existing event loop continues running long enough for all scheduled tasks to finish processing before concluding. Without waiting, closing the loop prematurely could cause unfinished tasks to be canceled.

Recap

We've explored the AsyncIOEventEmitter class in depth:

• The AsyncIOEventEmitter inherits from the EventEmitter class
• To use it, instantiate the class and call methods like emit()

  By understanding these concepts, you can effectively utilize the AsyncIOEventEmitter to emit events in both synchronous and asynchronous contexts, benefiting from the concurrency features provided by the AsyncIO framework.