atomcache

Introduction

Asynchronous cache manager designed for horizontally scaled web applications. NOTE: Currently has implementation only for FastAPI using Redis.

Requirements

Python 3.7+

• redis for cache implementation.
• FastAPI for the web parts.

Installation

$ pip install atomcache

---> 100%

Explanation schema

As UML

@startuml
    !theme materia
    participant Redis
    participant Instance_A as A
    participant Instance_B as B
    participant Instance_N as C


    B <-> Redis: GET: Cache=null & GET: Lock=null

    B <-> Redis: SET: Lock = true

    activate B #Red
    A <--> Redis: GET: Cache=null & GET: Lock=true
    activate A #Transparent
    C <--> Redis: GET: Cache=null & GET: Lock=true
    activate C #Transparent
    B <--> B: Do the computation
    B -> Redis: SET: Cache={...}
    deactivate B

    group Notify Cache SET
        Redis -> C
        Redis -> A
    end
    group GET Cache
        Redis <-> C
    deactivate C
        Redis <-> A
    deactivate A
    end
@enduml

Examples:

Usage as FastAPI Dependency

• Create a file events.py with:

from typing import Optional, Callable

from redis.asyncio import Redis
from fastapi import FastAPI, Depends
from atomcache import Cache


def create_start_app_handler(app: FastAPI) -> Callable:
    async def start_app() -> None:
        redis: Redis = await Redis.from_url(url="redis://localhost", encoding="utf-8")
        await Cache.init(app, redis)

    return start_app


def create_stop_app_handler(app: FastAPI) -> Callable:
    async def stop_app() -> None:
        await Cache.backend.close()

    return stop_app

• Create a file main.py with:

from typing import Optional

from fastapi import FastAPI, Depends
from atomcache import Cache

from .events import create_start_app_handler, create_stop_app_handler

app = FastAPI()

app.add_event_handler("startup", create_start_app_handler(app))
app.add_event_handler("shutdown", create_stop_app_handler(app))


@router.get("/resources", response_model=List[TheResponseModel], name="main:test-example")
async def resources(offset: int = 0, items: int = 10, cache: Cache = Depends(Cache(exp=600)):
    cache_id = f"{offset}-{items}"  # Build cache identifier
    await cache.raise_try(cache_id)  # Try to respond from cache
    response = await db.find(TheResponseModel, skip=offset, limit=items)
    await asyncio.sleep(10)  # Do some heavy work for 10 sec, see `lock_timeout`
    return cache.set(response, cache_id=cache_id)

Direct cache usage for avoiding repetitive calling on external resources:

from aiohttp import ClientSession
from atomcache import Cache

cache = Cache(exp=1200, namespace="my-namespace:")


async def requesting_helper(ref: str) -> List[dict]:
    cached_value = await cache.get(cache_id=ref)
    if cached_value is not None:
        return cached_value

    async with ClientSession() as session:
        async with session.get(f"https://external-api.io/{ref}") as response:
            if response.ok:
                cached_value = response.json()
                return cache.set(cached_value, cache_id=ref)
    return []