zloop 0.0.0

An asyncio event loop with a Zig core.

zloop

[!WARNING] zloop is experimental. The API and behaviour may change at any time, and it is not yet ready for production use.

A drop-in asyncio event loop whose engine is written in Zig. It's to asyncio what uvloop is - a real asyncio.AbstractEventLoop - except the engine is a hand-written kqueue/epoll reactor in Zig rather than libuv wrapped in Cython.

import asyncio
import zloop

print(asyncio.run(asyncio.sleep(0, "hello from a Zig loop"), loop_factory=zloop.new_event_loop))

With uvicorn:

uvicorn app:app --loop zloop:new_event_loop

Why

• Drop-in. A genuine AbstractEventLoop, so the asyncio ecosystem - uvicorn, FastAPI, AnyIO, HTTPX - runs on it unchanged.
• Correct. Passes uvicorn's entire test suite (1048 tests), identical to stock asyncio, plus its own suite at 100% coverage.
• Fast. Faster than uvloop on the workloads measured so far - scheduling, timers, and small/medium-message socket throughput (e.g. call_soon +46%, 1 KiB echo +16% on CPython 3.14 / macOS arm64). create_future ties, because all three loops reuse CPython's C-accelerated _asyncio.Future.

Benchmarks

The fairest comparison is uvloop's own echo benchmark, run unchanged except for a --zloop server flag mirroring --uvloop (the client is byte-for-byte uvloop's). Requests/sec, higher is better - macOS arm64, CPython 3.14, 3 workers, best of 3:

Message	Server mode	asyncio	uvloop	zloop	zloop vs uvloop
1 KiB	proto	113k	113k	121k	+7%
1 KiB	buffered	115k	115k	123k	+7%
1 KiB	streams	83k	90k	103k	+14%
10 KiB	proto	105k	110k	113k	+3%
10 KiB	buffered	105k	105k	124k	+18%
10 KiB	streams	81k	86k	95k	+11%

For the 1-10 KiB messages common in HTTP, WebSocket frames, and RPC, zloop leads uvloop in every cell. The 100 KiB row is omitted: at that size the test measures loopback bandwidth, not the loop, and all three swing wildly run-to-run.

Reproduce it with scripts/bench (or bash bench_uvloop/run_matrix.sh for the full matrix); the Benchmark CI workflow runs it on Linux and posts the table to the run summary.

How it works

The loop engine lives in Zig; CPython is reused only where reimplementing would be reckless: driving coroutines (asyncio.Future / asyncio.Task) and the TLS state machine (asyncio.sslproto). That's exactly uvloop's boundary.

zloop/            Python edge - new_event_loop() factory, connection setup
src/python/*.zig  CPython C-API adapter - Loop, Handle, Transport
src/core/*.zig    pure-Zig domain - run-once engine, kqueue/epoll reactor, timer heap