Async Runner

Async Runner is a minimal Python utility designed to run asynchronous tasks from synchronous code — without worrying about event loop conflicts or lifecycle issues.

Why Async Runner?

In many real-world projects, especially when integrating third-party libraries or legacy synchronous code, you may need to invoke async functions inside a sync context. However, common approaches come with challenges:

• asyncio.run() creates a new event loop, which fails if one already exists.
• Some libraries require an existing event loop, others fail if one already exists.
• Solutions like greenlet can be overly complex or unsuitable for certain use cases.

After struggling with these limitations across different projects, this package was built to offer a clean, lightweight, and thread-safe solution by:

✅ Delegating async tasks to a background thread
✅ Maintaining a single, long-running event loop
✅ Making async-in-sync calls as easy as a regular function call

Installation

pip install async2sync

✅ Features

• Simple, one-line usage
• Thread-safe and reusable
• Works in environments with or without existing event loops
• Avoids RuntimeError: Event loop is closed or This event loop is already running issues

How It Works

async_runner creates and manages an event loop inside a dedicated background thread. This allows your sync code to safely schedule and await asynchronous tasks, without interfering with the main thread’s context.

Example Usage

import asyncio
from async_runner import run_async

async def async_task():
    await asyncio.sleep(1)
    return "Async task completed"

def sync_task():
    result = run_async(async_task())
    print(result)

sync_task()

Output:

Async task completed

Use Cases

• Calling async APIs from FastAPI views or Python Scripts
• Wrapping async logic inside a sync SDK
• Integrating with libraries that inconsistently depend on event loop presence