Initial Commit

kv/lib/kv.ex

@@ -0,0 +1,10 @@
+defmodule KV do
+  use Application
+
+  @impl true
+  def start(_type, _args) do
+    # Anche se non usiamo KV.Supervisor name direttamente,
+    # e' comodo per debug
+    KV.Supervisor.start_link(name: KV.Supervisor)
+  end
+end

kv/lib/kv/bucket.ex

@@ -0,0 +1,33 @@
+defmodule KV.Bucket do
+  use Agent, restart: :temporary
+
+  @doc """
+  Starts a new bucket.
+  """
+  def start_link(_opts) do
+    Agent.start_link(fn -> %{} end)
+  end
+
+  @doc """
+  Gets a value from the `bucket` by `key`.
+  """
+  def get(bucket, key) do
+    Agent.get(bucket, &Map.get(&1, key))
+  end
+
+  @doc """
+  Puts the `value` for the given `key` in the `bucket`.
+  """
+  def put(bucket, key, value) do
+    Agent.update(bucket, &Map.put(&1, key, value))
+  end
+
+  @doc """
+  Deletes `key` from `bucket`.
+
+  Returns the current value of `key`, if `key` exists.
+  """
+  def delete(bucket, key) do
+    Agent.get_and_update(bucket, &Map.pop(&1, key))
+  end
+end

kv/lib/kv/registry.ex

@@ -0,0 +1,69 @@
+defmodule KV.Registry do
+  use GenServer
+
+  # Client API
+  @doc """
+  Starts the registry.
+  """
+  def start_link(opts) do
+    server = Keyword.fetch!(opts, :name)
+    GenServer.start_link(__MODULE__, server, opts)
+  end
+
+  @doc """
+  Looks up the bucket pid for `name` stored in `server`.
+
+  Returns `{:ok, pid}` if the bucket exists, `:error` otherwise.
+  """
+  def lookup(server, name) do
+    case :ets.lookup(server, name) do
+      [{^name, pid}] -> {:ok, pid}
+      [] -> :error
+    end
+  end
+
+  @doc """
+  Ensures there is a bucket associated with the given `name` in `server`.
+  """
+  def create(server, name) do
+    GenServer.call(server, {:create, name})
+  end
+
+  # Server Callbacks
+
+  @impl true
+  def init(table) do
+    # name -> bucket
+    names = :ets.new(table, [:named_table, read_concurrency: true])
+    refs = %{} # ref -> name
+    {:ok, {names, refs}}
+  end
+
+  @impl true
+  def handle_call({:create, name}, _from, {names, refs}) do
+    case lookup(names, name) do
+      {:ok, bucket} ->
+        {:reply, bucket, {names, refs}}
+      :error ->
+        {:ok, bucket} = DynamicSupervisor.start_child(KV.BucketSupervisor, KV.Bucket)
+        ref = Process.monitor(bucket)
+        refs = Map.put(refs, ref, name)
+        :ets.insert(names, {name, bucket})
+        {:reply, bucket, {names, refs}}
+    end
+  end
+
+  @impl true
+  def handle_info({:DOWN, ref, :process, _pid, _reason}, {names, refs}) do
+    {name, refs} = Map.pop(refs, ref)
+    :ets.delete(names, name)
+    {:noreply, {names, refs}}
+  end
+
+  @impl true
+  def handle_info(msg, state) do
+    require Logger
+    Logger.debug("Unexpected message in KV.Registry: #{inspect(msg)}")
+    {:noreply, state}
+  end
+end

kv/lib/kv/supervisor.ex

@@ -0,0 +1,17 @@
+defmodule KV.Supervisor do
+  use Supervisor
+
+  def start_link(opts) do
+    Supervisor.start_link(__MODULE__, :ok, opts)
+  end
+
+  @impl true
+  def init(:ok) do
+    children = [
+      {DynamicSupervisor, name: KV.BucketSupervisor, strategy: :one_for_one},
+      {KV.Registry, name: KV.Registry},
+    ]
+
+    Supervisor.init(children, strategy: :one_for_all)
+  end
+end