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TonIO

TonIO is a multi-threaded async runtime for free-threaded Python, built in Rust on top of the mio crate, and inspired by tinyio, trio and tokio.

Warning: TonIO is currently a work in progress and in alpha state. The APIs are subtle to breaking changes.

Note: TonIO is available on free-threaded Python and Unix systems only.

TonIO supports both using yield and the more canonical async/await notations, with the latter being available as part of the tonio.colored module. Following code snippets show both the usages.

Warning: despite the fact TonIO supports async and await notations, it's not compatible with any asyncio object like futures and tasks.

In a nutshell

yield syntax

import tonio

def wait_and_add(x: int) -> int:
    yield tonio.sleep(1)
    return x + 1

def foo():
    four, five = yield tonio.spawn(
        wait_and_add(3), 
        wait_and_add(4)
    )
    return four, five

out = tonio.run(foo())
assert out == (4, 5)

await syntax

import tonio.colored as tonio

async def wait_and_add(x: int) -> int:
    await tonio.sleep(1)
    return x + 1

async def foo():
    four, five = await tonio.spawn(
        wait_and_add(3), 
        wait_and_add(4)
    )
    return four, five

out = tonio.run(foo())
assert out == (4, 5)

Usage

Entrypoint

Every TonIO program consist of an entrypoint, which should be passed to the run method:

yield syntax

import tonio

def main():
    yield
    print("Hello world")

tonio.run(main())

await syntax

import tonio.colored as tonio

async def main():
    await tonio.yield_now()
    print("Hellow world")

tonio.run(main())

TonIO also provides a main decorator, thus we can rewrite the previous example as:

yield syntax

import tonio

@tonio.main
def main():
    yield
    print("Hello world")

main()

await syntax

import tonio.colored as tonio

@tonio.main
async def main():
    await tonio.yield_now()
    print("Hello world")

main()

Note: as you can see the colored module provides the additional yield_now coroutine, a quick way to define a suspension point, given you cannot just yield as in the non-colored notation.

Note: both run and main can only be called once per program. To run the runtime multiple times in the same program, follow the section below.

Manually managing the runtime

TonIO also provides the runtime function, to manually manage the runtime lifecycle:

import tonio

def _run1():
    ...

async def _run2():
    ...

def main():
    runtime = tonio.runtime()
    runtime.run_until_complete(_run1())
    runtime.run_until_complete(_run2())

Runtime options

The run, main and runtime methods accept options, specifically:

option name description default
context enable contextvars usage in coroutines False
signals list of signals to listen to
threads Number of runtime threads # of CPU cores
blocking_threadpool_size Maximum number of blocking threads 128
blocking_threadpool_idle_ttl Idle timeout for blocking threads (in seconds) 30

Events

The core object in TonIO is Event. It's basically a wrapper around an atomic boolean flag, initialised with False. Event provides the following methods:

  • is_set(): return the value of the flag
  • set(): set the flag to True
  • clear(): set the flag to False
  • wait(timeout=None): returns a coroutine you can yield on that unblocks when the flag is set to True or the timeout expires. Timeout is in seconds.

yield syntax

import tonio

@tonio.main
def main():
    event = tonio.Event()

    def setter():
        yield tonio.sleep(1)
        event.set()

    tonio.spawn(setter())
    yield event.wait()

await syntax

import tonio.colored as tonio

@tonio.main
async def main():
    event = tonio.Event()

    async def setter():
        await tonio.sleep(1)
        event.set()

    tonio.spawn(setter())
    await event.wait()

Spawning tasks

TonIO provides the spawn method to schedule new coroutines onto the runtime:

yield syntax

import tonio

def doubv(v):
    yield
    return v * 2

@tonio.main
def main():
    parallel = tonio.spawn(doubv(2), doubv(3))
    v3 = yield doubv(4)
    v1, v2 = yield parallel
    print([v1, v2, v3])

await syntax

import tonio.colored as tonio

async def doubv(v):
    await tonio.yield_now()
    return v * 2

@tonio.main
async def main():
    parallel = tonio.spawn(doubv(2), doubv(3))
    v3 = await doubv(4)
    v1, v2 = await parallel
    print([v1, v2, v3])

Coroutines passed to spawn get schedule onto the runtime immediately. Using yield or await on the return value of spawn just waits for the coroutines to complete and retreive the results.

Blocking tasks

TonIO provides the spawn_blocking method to schedule blocking operations onto the runtime:

yield syntax

import tonio

def read_file(path):
    with open(file, "r") as f:
        return f.read()

@tonio.main
def main():
    file_data = yield tonio.spawn_blocking(
        read_file, 
        "sometext.txt"
    )

await syntax

import tonio.colored as tonio

def read_file(path):
    with open(file, "r") as f:
        return f.read()

@tonio.main
async def main():
    file_data = await tonio.spawn_blocking(
        read_file, 
        "sometext.txt"
    )

Map utilities

TonIO provides the map and map_blocking utilities to spawn the same operation with an iterable of parameters:

yield syntax

import tonio

accum = []

def task(no):
    yield tonio.sleep(0.5)
    accum.append(no * 2)

@tonio.main
def main():
    yield tonio.map(task, range(4))

await syntax

import tonio.colored as tonio

accum = []

async def task(no):
    await tonio.sleep(0.5)
    accum.append(no * 2)

@tonio.main
async def main():
    await tonio.map(task, range(4))

Scopes and cancellations

TonIO provides a scope context, that lets you cancel work spawned within it:

yield syntax

import tonio

def slow_push(target, sleep):
    yield tonio.sleep(sleep)
    target.append(True)

@tonio.main
def main():
    values = []
    with tonio.scope() as scope:
        scope.spawn(_slow_push(values, 0.1))
        scope.spawn(_slow_push(values, 2))
        yield tonio.sleep(0.2)
        scope.cancel()
    yield scope()
    assert len(values) == 1

await syntax

import tonio.colored as tonio

async def slow_push(target, sleep):
    await tonio.sleep(sleep)
    target.append(True)

@tonio.main
async def main():
    values = []
    async with tonio.scope() as scope:
        scope.spawn(_slow_push(values, 0.1))
        scope.spawn(_slow_push(values, 2))
        await tonio.sleep(0.2)
        scope.cancel()
    assert len(values) == 1

When you yield on the scope, it will wait for all the spawned coroutines to end. If the scope was canceled, then all the pending coroutines will be canceled.

Note: as you can see, the colored version of scope doesn't require to be awaited, as it will yield when exiting the context.

Time-related functions

  • tonio.time.time(): a function returning the runtime's clock (in seconds, microsecond resolution)
  • tonio.time.sleep(delay): a coroutine you can yield on to sleep (delay is in seconds)
  • tonio.time.timeout(coro, timeout): a coroutine you can yield on returning a tuple (output, success). If the coroutine succeeds in the given time then the pair (output, True) is returned. Otherwise this will return (None, False).

Note: time.sleep is also exported to the main tonio module.

Note: all of the above functions are also present in tonio.colored.time module.

Scheduling work

TonIO provides the time.interval function to create interval objects you can yield on a scheduled basis:

yield syntax

import tonio
from tonio import time

def some_task():
    ...

def scheduler():
    interval = time.interval(1)
    while True:
        yield interval.tick()
        tonio.spawn(some_task())

@tonio.main
def main():
    tonio.spawn(scheduler())
    # do some other work

await syntax

import tonio.colored as tonio
from tonio.colored import time

async def some_task():
    ...

async def scheduler():
    interval = time.interval(1)
    while True:
        await interval.tick()
        tonio.spawn(some_task())

@tonio.main
async def main():
    tonio.spawn(scheduler())
    # do some other work

The interval method first argument is the interval in seconds resolution, and the method also accepts an optional at argument, to delay the first execution at a specific time (from the runtime's clock perspective):

from tonio import time

# tick every 500ms, with the first tick happening in 5 seconds from now
interval = time.interval(0.5, time.time() + 5)

Synchronization primitives

Synchronization primitives are exposed in the tonio.sync module.

Lock

Implements a classic mutex, or a non-reentrant, single-owner lock for coroutines:

yield syntax

import tonio
from tonio import sync

@tonio.main
def main():
    # counter can't go above 1
    counter = 0

    def _count(lock):
        nonlocal counter
        with (yield lock()):
            counter += 1
            yield
            counter -= 1
    
    lock = sync.Lock()
    yield tonio.spawn(*[
        _count(lock)
        for _ in range(10)
    ])

await syntax

import tonio.colored as tonio
from tonio.colored import sync

@tonio.main
async def main():
    # counter can't go above 1
    counter = 0

    async def _count(lock):
        nonlocal counter
        async with lock:
            counter += 1
            await tonio.yield_now()
            counter -= 1
    
    lock = sync.Lock()
    await tonio.spawn(*[
        _count(lock)
        for _ in range(10)
    ])

The Lock object also implements an or_raise method, that will immediately fail when the lock cannot be acquired:

from tonio.exceptions import WouldBlock

try:
    with lock.or_raise():
        ...
except WouldBlock:
    ...

Semaphore

A semaphore for coroutines:

yield syntax

import tonio
from tonio import sync

@tonio.main
def main():
    # counter can't go above 2
    counter = 0

    def _count(semaphore):
        nonlocal counter
        with (yield semaphore()):
            counter += 1
            yield
            counter -= 1
    
    semaphore = sync.Semaphore(2)
    yield tonio.spawn(*[
        _count(semaphore)
        for _ in range(10)
    ])

await syntax

import tonio.colored as tonio
from tonio.colored import sync

@tonio.main
async def main():
    # counter can't go above 2
    counter = 0

    async def _count(semaphore):
        nonlocal counter
        async with semaphore:
            counter += 1
            await tonio.yield_now()
            counter -= 1
    
    semaphore = sync.Semaphore(2)
    await tonio.spawn(*[
        _count(semaphore)
        for _ in range(10)
    ])

As for locks, the Semaphore object also implements an or_raise method, that will immediately fail when the lock cannot be acquired:

from tonio.exceptions import WouldBlock

try:
    with semaphore.or_raise():
        ...
except WouldBlock:
    ...

The Semaphore object also implements a tokens method, that returns the number of available tokens.

Barrier

A barrier for coroutines:

yield syntax

import tonio
from tonio import sync

@tonio.main
def main():
    barrier = sync.Barrier(3)
    count = 0

    def _start_at_3():
        nonlocal count
        count += 1
        i = yield barrier.wait()
        assert count == 3
        return i

    yield tonio.spawn(*[
        _start_at_3()
        for _ in range(3)
    ])

await syntax

import tonio.colored as tonio
from tonio.colored import sync

@tonio.main
async def main():
    barrier = sync.Barrier(3)
    count = 0

    async def _start_at_3():
        nonlocal count
        count += 1
        i = await barrier.wait()
        assert count == 3
        return i

    await tonio.spawn(*[
        _start_at_3()
        for _ in range(3)
    ])

The Barrier object also implements a value method, which returns the current value of the barrier.

Channels

Multi-producer multi-consumer channels for inter-coroutine communication.

The tonio.sync.channel module provides both a channel and an unbounded constructors.
The main difference between bounded and unbounded channels, as the names suggest, is that while the first will suspend sending messages once the specified length is reached, and it will resume accepting messages once the existing buffer is consumed, the latter will always accept new messages. That's also why, the sender part of a bounded channel is async, while in the unbounded is not.

Bounded channel

yield syntax

import tonio
from tonio import sync
from tonio.sync import channel

def producer(sender, barrier, offset):
    for i in range(20):
        message = offset + 1
        yield sender.send(message)
    yield barrier.wait()

def consumer(receiver):
    while True:
        try:
            message = yield receiver.receive()
            print(message)
        except Exception:
            break

@tonio.main
def main():
    def close(sender, barrier):
        yield barrier.wait()
        sender.close()

    sender, receiver = channel.channel(2)
    barrier = sync.Barrier(3)
    yield tonio.spawn(*[
        producer(sender, barrier, 100),
        producer(sender, barrier, 200),
        consumer(receiver),
        consumer(receiver),
        consumer(receiver),
        consumer(receiver),
        close(sender, barrier),
    ])

await syntax

import tonio.colored as tonio
from tonio.colored import sync
from tonio.colored.sync import channel

async def producer(sender, barrier, offset):
    for i in range(20):
        message = offset + 1
        await sender.send(message)
    await barrier.wait()

async def consumer(receiver):
    while True:
        try:
            message = await receiver.receive()
            print(message)
        except Exception:
            break

@tonio.main
async def main():
    async def close(sender, barrier):
        await barrier.wait()
        sender.close()

    sender, receiver = channel.channel(2)
    barrier = sync.Barrier(3)
    await tonio.spawn(*[
        producer(sender, barrier, 100),
        producer(sender, barrier, 200),
        consumer(receiver),
        consumer(receiver),
        consumer(receiver),
        consumer(receiver),
        close(sender, barrier),
    ])
Unbounded channel

yield syntax

import tonio
from tonio import sync
from tonio.sync import channel

def producer(sender, barrier, offset):
    for i in range(20):
        message = offset + 1
        sender.send(message)
    yield barrier.wait()

def consumer(receiver):
    while True:
        try:
            message = yield receiver.receive()
            print(message)
        except Exception:
            break

@tonio.main
def main():
    def close(sender, barrier):
        yield barrier.wait()
        sender.close()

    sender, receiver = channel.unbounded()
    barrier = sync.Barrier(3)
    yield tonio.spawn(*[
        producer(sender, barrier, 100),
        producer(sender, barrier, 200),
        consumer(receiver),
        consumer(receiver),
        consumer(receiver),
        consumer(receiver),
        close(sender, barrier),
    ])

await syntax

import tonio.colored as tonio
from tonio.colored import sync
from tonio.colored.sync import channel

async def producer(sender, barrier, offset):
    for i in range(20):
        message = offset + 1
        sender.send(message)
    await barrier.wait()

async def consumer(receiver):
    while True:
        try:
            message = await receiver.receive()
            print(message)
        except Exception:
            break

@tonio.main
async def main():
    async def close(sender, barrier):
        await barrier.wait()
        sender.close()

    sender, receiver = channel.unbounded()
    barrier = sync.Barrier(3)
    await tonio.spawn(*[
        producer(sender, barrier, 100),
        producer(sender, barrier, 200),
        consumer(receiver),
        consumer(receiver),
        consumer(receiver),
        consumer(receiver),
        close(sender, barrier),
    ])

Network module

Network primitives are exposed under the tonio.net module.

Streams

The high-level network primitives in TonIO are centered aroud the SocketStream and SocketListener objects.

The SocketListener object implements an accept coroutine which returns a SocketStream object.
The SocketStream object implements the send_all and receive_some coroutines to send and receive data.
Both objects implement a close method to shutdown the underlying socket.

You can create and interact with the above objects using some high-level helpers in the net module, specifically:

  • open_tcp_stream: a coroutine to open a SocketStream connected to a TCP endpoint
  • open_unix_socket: a coroutine to open a SocketStream connected to an Unix socket
  • open_tcp_listeners: a coroutine to initialise SocketListener objects
  • serve_listeners: a coroutine to spawn SocketListener accept loops targeting a handler
  • serve_tcp: a coroutine that join open_tcp_listener and serve_listeners in one call

yield syntax

from tonio.net import open_tcp_stream, serve_tcp

def server():
    yield serve_tcp(
        server_handle, 
        host='127.0.0.1', 
        port=8000
    )

def server_handle(stream):
    # receive some data
    data = yield stream.receive_some()

def client():
    stream = yield open_tcp_stream(
        host='127.0.0.1', 
        port=8000
    )
    # send some data
    yield stream.send_all("message")

await syntax

from tonio.colored.net import open_tcp_stream, serve_tcp

async def server():
    await serve_tcp(
        server_handle, 
        host='127.0.0.1', 
        port=8000
    )

async def server_handle(stream):
    # receive some data
    data = await stream.receive_some()

async def client():
    stream = await open_tcp_stream(
        host='127.0.0.1', 
        port=8000
    )
    # send some data
    await stream.send_all("message")

SSL streams

TonIO implement SSL wrappers around the streaming APIs through primitives in the tonio.net.ssl module.

TonIO provides the SSLStream and SSLListener object wrappers and the following high-level helpers:

  • open_ssl_over_tcp_stream: a coroutine to open a SSLStream wrapping a TCP SocketStream
  • open_ssl_over_tcp_listeners: a coroutine to initialise SSLListener objects
  • serve_ssl_over_tcp: a coroutine that join open_tls_over_tcp_listeners and serve_listeners in one call

Low-level sockets

The tonio.net.socket module provides TonIO's basic low-level networking API.
Generally, the API exposed by this module mirrors the standard library socket module.

TonIO socket objects are overall very similar to the standard library socket objects, with the main difference being that blocking methods become coroutines.

yield syntax

import tonio
from tonio.net import socket

def server():
    sock = socket.socket()
    with sock:
        yield sock.bind(('127.0.0.1', 8000))
        sock.listen()

        while True:
            client, _ = yield sock.accept()
            tonio.spawn(server_handle(client))

def server_handle(connection):
    with connection:
        # receive some data
        data = yield connection.recv(4096)

def client():
    sock = socket.socket()
    with sock:
        yield sock.connect(('127.0.0.1', 8000))
        yield sock.send("message")

await syntax

import tonio.colored as tonio
from tonio.colored.net import socket

async def server():
    sock = socket.socket()
    with sock:
        await sock.bind(('127.0.0.1', 8000))
        sock.listen()

        while True:
            client, _ = await sock.accept()
            tonio.spawn(server_handle(client))

async def server_handle(connection):
    with connection:
        # receive some data
        data = await connection.recv(4096)

async def client():
    sock = socket.socket()
    with sock:
        await sock.connect(('127.0.0.1', 8000))
        await sock.send("message")

Signals

TonIO provides a context manager to catch signals.

The usage of such context manager requires to first configure the runtime to listen for such signals:

yield syntax

import signal
import tonio
from tonio.time import interval

def sig_handle():
    with tonio.signal_receiver(
        signal.SIGHUP, 
        signal.SIGUSR1
    ) as sigs:
        for ev in sigs:
            sig = yield ev
            if sig == signal.SIGHUP:
                ...

@tonio.main(
    signals=[signal.SIGHUP, signal.SIGUSR1]
)
def main():
    tonio.spawn(sig_handle())
    ticker = interval(1)
    while True:
        yield ticker.tick()

await syntax

import signal
import tonio.colored as tonio
from tonio.colored.time import interval

async def sig_handle():
    with tonio.signal_receiver(
        signal.SIGHUP, 
        signal.SIGUSR1
    ) as sigs:
        async for sig in sigs:
            if sig == signal.SIGHUP:
                ...

@tonio.main(
    signals=[signal.SIGHUP, signal.SIGUSR1]
)
async def main():
    tonio.spawn(sig_handle())
    ticker = interval(1)
    while True:
        await ticker.tick()

License

TonIO is released under the BSD License.

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A multi-threaded async runtime for Python

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TonIO 0.3.0 Latest
Mar 28, 2026
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