aiolifecycle 0.1.8
Micro-framework to effectively run asyncio functions in synchronous contexts
License: Apache License 2.0

# aiolifecycle

Safely use asyncio handlers in synchronous context.

## Use case

If you want to run an asyncio-based program in a synchronous context - such as
a command line invocation - you can use `asyncio.run` from the standard library.
But it immediately spins up and terminates an event loop. What if you want to a
continuous workflow, where you can initialise and re-use resources?

The original need for this project arose when adapting an asyncio-based system
to AWS Lambda, which makes multiple synchronous function calls in the same
interpreter environment.

## Installation

Run `pip install aiolifecycle`, or add it to your package dependencies.

## Usage

### Handler

Define your handler as an `async` function, and add the `sync` annotation. Then
it can safely be called synchronously. An event loop will automatically be
initialised with its associated resources.


```python
import asyncio

from aiolifecycle import sync


@sync()
async def my_handler() -> None:
    await asyncio.sleep(1)
```

By default, handlers are *eager*, meaning an event loop will be created and
initialisation functions will be immediately run on module import.

If you want to initialise resources only when a handler is first called, do:

```python
import asyncio

from aiolifecycle import sync


@sync(eager=False)
async def my_handler() -> None:
    await asyncio.sleep(1)
```

### Initialisation

You can define `async` initialisation functions to prepare resources for use by
handlers. These can be simple `async def`s returning nothing.

In the following example, `my_init` will be called exactly once, before any handlers
run.

```python
import asyncio

from aiolifecycle import sync, init


@init
async def my_init() -> None:
    print('Hello, world!')


@sync
async def my_handler() -> None:
    await asyncio.sleep(1)
```

Initialisation order can be controlled with the `order` parameter. In the following
example, `hello` will be called before `world`. Functions with the same order (or
undefined order) are called in the order they were defined.

```python
import asyncio

from aiolifecycle import sync, init

@init(order=20)
async def world() -> None:
    print('World!')


@init(order=10)
async def hello() -> None:
    print('Hello!')


@sync()
async def my_handler() -> None:
    await asyncio.sleep(1)

```

Initialisation functions can manage resources. You can simply return the resource
from an `init` function (if no finalisation is necessary), or define it as an
`asynccontextmanager`

Or you can use `AsyncContextManagers`, and access the resources they create by
refering to the handler function. Proper lifetime will be managed internally, such
that the initialisation will happen once.

```python
import json
from contextlib import asynccontextmanager
from typing import AsyncIterator

import aiofiles
from aiofiles.threadpool.text import AsyncTextIOWrapper

from aiolifecycle import sync
from aiolifecycle import init


@init
async def json_log_path() -> str:
    # Run complicated logic to determine path, only once!
    # ....
    return '/tmp/my-file.json'


@init()
@asynccontextmanager
async def json_log_file() -> AsyncIterator[AsyncTextIOWrapper]:
    log_path = await json_log_path()
    # File will be open before any handler is called, and cleaned up on shutdown
    async with aiofiles.open(log_path, mode='a') as f:
        yield f


@sync()
async def handler():
    log_file = await json_log_file()
    await log_file.write(json.dumps(event) + "\n")
    await log_file.flush()
```

# Changelog

<!--next-version-placeholder-->

## v0.1.8 (2022-05-11)
### Fix
* **init:** Fix cycle checking scope ([`9e76ea7`](https://github.com/danielkza/aiolifecycle-py/commit/9e76ea703027ac514adbc1c7822324d77e089c19))

## v0.1.7 (2022-05-11)
### Fix
* **init:** Raise terminating exception on init function failure bubbling up ([`69c0f88`](https://github.com/danielkza/aiolifecycle-py/commit/69c0f8890faca5cb0ff341bfa3b75aea465125cd))
* **init:** Raise terminating exception on init function failure bubbling up ([`024734d`](https://github.com/danielkza/aiolifecycle-py/commit/024734d0e13ab145a529056be495bf9de8fe4746))

## v0.1.6 (2022-05-11)
### Fix
* **init:** Exit immediately on init failure ([`8abe43b`](https://github.com/danielkza/aiolifecycle-py/commit/8abe43b71344445bc42c8003a3ca89508e7409b1))

## v0.1.5 (2022-05-11)
### Fix
* **init:** Exit immediately on init failure ([`9652c7c`](https://github.com/danielkza/aiolifecycle-py/commit/9652c7ce68941826a55be3892d07cac78d27924c))

## v0.1.4 (2022-05-10)
### Fix
* **init:** Fix threading atexit registration order ([`0a3a861`](https://github.com/danielkza/aiolifecycle-py/commit/0a3a861cd01b1b7c34acb253d08a8a05538c7930))

## v0.1.3 (2022-05-09)
### Fix
* **loop:** Wait for loop on interpreter termination ([`e6b9825`](https://github.com/danielkza/aiolifecycle-py/commit/e6b9825ce38134af160ed77c06f0bfb47eef2a83))

## v0.1.2 (2022-05-09)
### Fix
* **init:** Add missing reset for context var ([#1](https://github.com/danielkza/aiolifecycle-py/issues/1)) ([`fc7f654`](https://github.com/danielkza/aiolifecycle-py/commit/fc7f6546711002abb84343bde080b17cf8da97f2))

## v0.1.1 (2022-05-05)
### Fix
* **license:** Update copyright ([`588e5a3`](https://github.com/danielkza/aiolifecycle-py/commit/588e5a3602672310bc76f4077dc0a100953982e4))

## v0.1.0 (2022-05-05)
### Feature
* **all:** Remove remaining lambda references ([`c003c73`](https://github.com/danielkza/aiolifecycle-py/commit/c003c736836e7e59828d10fe494f786345d6e5ec))

## v0.0.4 (2022-05-05)
### Fix
* **handlers:** Cycle detection ([`018ba95`](https://github.com/danielkza/aiolifecycle-py/commit/018ba9507ab88c0f3b66e92d2723f83d0e732e98))
* **handlers:** Rename handlers to remove lambda references ([`de9643b`](https://github.com/danielkza/aiolifecycle-py/commit/de9643bfa4c1b7934d00c35c5e8a8a4441cc209a))
* **tests:** For new resource management ([`5f30e6d`](https://github.com/danielkza/aiolifecycle-py/commit/5f30e6d6f54b55166647947caadc62ae64a0528c))
* **metadata:** Use Markdown version of Apache License [skip ci] ([`bfaf82e`](https://github.com/danielkza/aiolifecycle-py/commit/bfaf82eb3efd0faaa0fcfd0610e3c5f960b17777))

## v0.0.3 (2022-05-04)
### Fix
* **cd:** Fix long_description Markdown content type ([`b3479ee`](https://github.com/danielkza/aiolifecycle-py/commit/b3479ee384df19062b09f42f976854ed0608f991))

## v0.0.2 (2022-05-04)
### Fix
* **cd:** Don't release on new tags ([`581d5ff`](https://github.com/danielkza/aiolifecycle-py/commit/581d5ffc6ec70737841f683e520b77288362df15))

## v0.0.1 (2022-05-04)
### Fix
* **cd:** Force release ([`7bbac93`](https://github.com/danielkza/aiolifecycle-py/commit/7bbac93ee910d88b4ac3ef9a0ff33c0e19af2bab))
* **cd:** Force release ([`dd9f209`](https://github.com/danielkza/aiolifecycle-py/commit/dd9f20986552004674a45f229d8a0e2f70188d96))
* **cd:** Force release ([`e621555`](https://github.com/danielkza/aiolifecycle-py/commit/e6215558d3cbdebf2809c09159f3a1f8d929f33b))

Copyright 2022 Daniel Miranda and contributors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

<http://www.apache.org/licenses/LICENSE-2.0>

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

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