Winloop

To install Winloop on your Windows operating system, use the standard pip command:

pip install winloop

If you wish to build the extension locally, you can clone the repository and run the setup script. Note that you must have Cython and Visual C++ extensions installed to compile the library.

python setup.py build_ext --inplace

To use Winloop with FastAPI, you must install the loop policy before starting the Uvicorn server. You can pass the Winloop event loop directly to the uvicorn.Config object.

from fastapi import FastAPI
import winloop
import uvicorn
import asyncio

app = FastAPI()

@app.on_event("startup")
def make_assertion():
    # Verify that Winloop is the active policy
    assert isinstance(asyncio.get_event_loop_policy(), winloop.WinLoopPolicy)

if __name__ == "__main__":
    winloop.install()
    loop = asyncio.get_event_loop()
    config = uvicorn.Config(app=app, port=10000, loop=loop)
    server = uvicorn.Server(config)
    asyncio.run(server.serve())

You can write platform-agnostic code that uses uvloop on Linux/macOS and winloop on Windows by checking the system platform and using the run function.

import sys
import asyncio

async def main():
    # Your async logic here
    pass

if __name__ == "__main__":
    if sys.platform in ('win32', 'cygwin', 'cli'):
        from winloop import run
    else:
        # if we're on apple or linux do this instead
        from uvloop import run
    run(main())

To use Winloop as your default asyncio event loop policy, call winloop.install(). This is typically done at the very beginning of your application's entry point.

import winloop

if __name__ == "__main__":
    winloop.install()
    # Your asyncio code here

Winloop provides significant performance improvements over the standard Windows asyncio event loop policies for TCP connections.

| Asyncio Event Loop Policy | Time (in Seconds) |
|---------------------------|--------------------|
| WinLoopPolicy             | 0.493s             |
| WindowsProactorEventLoopPolicy | 2.510s             |
| WindowsSelectorEventLoopPolicy | 2.723s             |

The preferred way to execute an asynchronous entry point using the winloop event loop is by calling winloop.run(). This function manages the lifecycle of the winloop.Loop, including creation, running the provided coroutine, and proper shutdown of tasks and generators. It is compatible with different Python versions (3.10+).

If you provide a custom loop_factory, it must return a winloop.Loop or a subtype of it.

import winloop
import asyncio

async def main():
    print("Running in winloop!")
    await asyncio.sleep(1)

if __name__ == '__main__':
    winloop.run(main())

Returns a new instance of winloop.Loop. Note that creating a loop does not automatically set it as the current event loop for the thread; you must use asyncio.set_event_loop() if you intend to use it manually.

import winloop

loop = winloop.new_event_loop()

The current version of the winloop package is available via the __version__ attribute. You can use this to verify your installation or ensure compatibility with other tools.

import winloop
print(winloop.__version__)