Define Cache and convert app to OTP

Define a simple in-memory key-value store for our cache.

TL;DR:
- Define `Cache` as a simple state-keeping `Agent`
- Define `Sup`, which starts our Cache process
- Define `App`, which starts our Supervisor process
- Whitelist `App` in `mix.exs`, so that it starts after calling `iex -S mix`
This commit is contained in:
William Carroll 2020-12-12 01:04:39 +00:00
parent c0a88ba7d5
commit 714ec29743
4 changed files with 58 additions and 1 deletions

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@ -0,0 +1,8 @@
defmodule App do
use Application
@impl true
def start(_type, _args) do
Sup.start_link()
end
end

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@ -0,0 +1,27 @@
defmodule Cache do
@moduledoc """
Cache is an in-memory key-value store.
"""
use Agent
@doc """
Inititalize the key-value store.
"""
def start_link(_) do
Agent.start_link(fn -> %{} end, name: __MODULE__)
end
@doc """
Attempt to return the value stored at `key`
"""
def get(key) do
Agent.get(__MODULE__, &Map.get(&1, key))
end
@doc """
Write the `value` under the `key`. Last writer wins.
"""
def put(key, value) do
Agent.update(__MODULE__, &Map.put(&1, key, value))
end
end

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@ -0,0 +1,21 @@
defmodule Sup do
@moduledoc """
Top-level supervisor for our OTP application. For now, this supervisor starts
and monitors our cache.
"""
use Supervisor
def start_link(opts \\ []) do
Supervisor.start_link(__MODULE__, :ok, opts)
end
@impl true
def init(:ok) do
children = [
Cache
]
Supervisor.init(children, strategy: :one_for_one)
end
end

View file

@ -14,7 +14,8 @@ defmodule Server.MixProject do
# Run "mix help compile.app" to learn about applications.
def application do
[
extra_applications: [:logger]
extra_applications: [:logger],
mod: {App, []}
]
end