Elixir & Phoenix: Scalable Backend Development · Pelajaran

Supervisor Dinamis dan Registry

Pelajari cara memulai dan menghentikan proses secara dinamis dengan `DynamicSupervisor` serta menggunakan `Registry` untuk mencari proses.

Pelajaran 3 dari 411 langkah

Supervisor Dinamis dan Registry adalah pelajaran Elixir & Phoenix: Scalable Backend Development gratis di CoddyKit. Ini adalah pelajaran 3 dari 4. Kamu bisa membaca pelajaran lengkapnya di bawah secara gratis — lalu praktikkan langsung di browser dengan editor kode bawaan dan tutor AI 24/7. Ini adalah bagian dari jalur belajar Elixir & Phoenix: Scalable Backend Development, dan progresmu tersinkronisasi di web dan aplikasi CoddyKit. Kursus Elixir & Phoenix: Scalable Backend Development mencakup 4 pelajaran total.

Bagian dari pelajaran ini belum diterjemahkan dan ditampilkan dalam bahasa Inggris.

Dynamic Process Management

In previous lessons, we learned about supervisors for managing a fixed set of processes. But what if your application needs to create or destroy processes on demand, like for each user session or a specific task?

This is where dynamic process management comes in handy. It allows your application to adapt and scale by creating processes only when they are needed.

Introducing DynamicSupervisor

Elixir's DynamicSupervisor is designed precisely for this purpose. Unlike Supervisor, which manages a predefined list of children, a DynamicSupervisor starts with no children.

It provides functions to dynamically add and remove child processes during runtime, giving you flexible control over your application's process tree.

Starting a DynamicSupervisor

To use a DynamicSupervisor, you first need to start it, typically within your application's supervision tree. Here's a basic setup:

defmodule MyApp.DynamicManager do
  use DynamicSupervisor

  def start_link(init_arg) do
    DynamicSupervisor.start_link(__MODULE__, init_arg, name: __MODULE__)
  end

  @impl true
  def init(_init_arg) do
    DynamicSupervisor.init(strategy: :one_for_one)
  end
end

# To run this in an IEx session:
# {:ok, pid} = MyApp.DynamicManager.start_link([])
# IO.puts("DynamicSupervisor started with PID: #{inspect(pid)}")

Adding Children Dynamically

Once your DynamicSupervisor is running, you can add new children using DynamicSupervisor.start_child/2. Each child needs a child specification defining how it should be started.

Let's create a simple GenServer that the supervisor can manage.

defmodule MyApp.Worker do
  use GenServer

  def start_link(id) do
    GenServer.start_link(__MODULE__, id, name: via_tuple(id))
  end

  def init(id) do
    IO.puts("Worker #{id} started!")
    {:ok, id}
  end

  defp via_tuple(id), do: {:via, Registry, {MyApp.Registry, id}}
end

defmodule MyApp.DynamicManager do
  use DynamicSupervisor

  def start_link(init_arg) do
    DynamicSupervisor.start_link(__MODULE__, init_arg, name: __MODULE__)
  end

  @impl true
  def init(_init_arg) do
    DynamicSupervisor.init(strategy: :one_for_one)
  end

  def start_worker(id) do
    child_spec = %{
      id: id,
      start: {MyApp.Worker, :start_link, [id]}
    }
    DynamicSupervisor.start_child(__MODULE__, child_spec)
  end
end

# To run this in an IEx session:
# {:ok, manager_pid} = MyApp.DynamicManager.start_link([])
# {:ok, worker_pid} = MyApp.DynamicManager.start_worker(:user_123)
# IO.puts("Worker PID: #{inspect(worker_pid)}")

Stopping Dynamic Children

Just as you can start children dynamically, you can also stop them. Use DynamicSupervisor.terminate_child/2 with the child's PID.

The supervisor will handle the graceful shutdown of the process.

defmodule MyApp.Worker do
  use GenServer

  def start_link(id) do
    GenServer.start_link(__MODULE__, id, name: {:global, id})
  end

  def init(id) do
    IO.puts("Worker #{id} started!")
    {:ok, id}
  end

  def terminate(_reason, id) do
    IO.puts("Worker #{id} stopping!")
  end
end

defmodule MyApp.DynamicManager do
  use DynamicSupervisor

  def start_link(init_arg) do
    DynamicSupervisor.start_link(__MODULE__, init_arg, name: __MODULE__)
  end

  @impl true
  def init(_init_arg) do
    DynamicSupervisor.init(strategy: :one_for_one)
  end

  def start_worker(id) do
    child_spec = %{id: id, start: {MyApp.Worker, :start_link, [id]}}
    DynamicSupervisor.start_child(__MODULE__, child_spec)
  end

  def stop_worker(worker_pid) do
    DynamicSupervisor.terminate_child(__MODULE__, worker_pid)
  end
end

# To run this in an IEx session:
# {:ok, manager_pid} = MyApp.DynamicManager.start_link([])
# {:ok, worker_pid} = MyApp.DynamicManager.start_worker(:task_A)
# :timer.sleep(100)
# MyApp.DynamicManager.stop_worker(worker_pid)
# :timer.sleep(100)
# IO.puts("Worker process should now be stopped.")

The Need for a Registry

When you start processes dynamically, how do you find them later? If you only have their PIDs, what happens if a process crashes and restarts with a new PID?

We need a way to assign a persistent, meaningful name to a process and look it up reliably, regardless of its current PID. This is where Elixir's Registry comes in.

What is Registry?

The Registry module provides a local, distributed, and fault-tolerant key-value store for associating arbitrary terms (keys) with process identifiers (PIDs).

It's perfect for looking up processes by a name or ID, especially when dealing with dynamic processes or when you want to use a custom name instead of global or local atoms.

Starting and Using Registry

Like other OTP behaviors, Registry needs to be started, typically as part of your application's supervision tree. You can define multiple registries, each with its own scope.

Once started, you can register processes with keys and look them up.

defmodule MyApp.Registry do
  use Registry, keys: :unique, name: __MODULE__
end

defmodule MyApp.WorkerWithRegistry do
  use GenServer

  def start_link(id) do
    GenServer.start_link(__MODULE__, id, name: {:via, Registry, {MyApp.Registry, id}})
  end

  def init(id) do
    IO.puts("Worker #{id} started and registered!")
    {:ok, id}
  end

  def get_state(pid) do
    GenServer.call(pid, :get_state)
  end

  @impl true
  def handle_call(:get_state, _from, state) do
    {:reply, state, state}
  end
end

# To run this in an IEx session:
# {:ok, _} = MyApp.Registry.start_link([]) # Start the registry
# {:ok, worker_pid} = MyApp.WorkerWithRegistry.start_link(:session_1)
# IO.puts("Registered worker PID: #{inspect(worker_pid)}")
#
# {:ok, [pid_found]} = Registry.lookup(MyApp.Registry, :session_1)
# IO.puts("Looked up PID: #{inspect(pid_found)}")
# IO.puts("Worker state: #{MyApp.WorkerWithRegistry.get_state(pid_found)}")

DynamicSupervisor with Registry

Combining DynamicSupervisor with Registry is a powerful pattern. You can dynamically start worker processes, and each worker registers itself with a unique key in the Registry.

This allows other parts of your application to find and interact with specific worker processes without needing their PIDs directly.

defmodule MyApp.UserSession do
  use GenServer

  def start_link(user_id) do
    # Register with Registry using the user_id as key
    GenServer.start_link(__MODULE__, user_id, name: {:via, Registry, {MyApp.SessionsRegistry, user_id}})
  end

  def init(user_id) do
    IO.puts("Session for user #{user_id} started.")
    {:ok, user_id}
  end

  def get_user_id(pid) do
    GenServer.call(pid, :get_user_id)
  end

  @impl true
  def handle_call(:get_user_id, _from, user_id) do
    {:reply, user_id, user_id}
  end
end

defmodule MyApp.SessionsRegistry do
  use Registry, keys: :unique, name: __MODULE__
end

defmodule MyApp.SessionSupervisor do
  use DynamicSupervisor

  def start_link(init_arg) do
    DynamicSupervisor.start_link(__MODULE__, init_arg, name: __MODULE__)
  end

  @impl true
  def init(_init_arg) do
    DynamicSupervisor.init(strategy: :one_for_one)
  end

  def start_session(user_id) do
    child_spec = %{
      id: user_id,
      start: {MyApp.UserSession, :start_link, [user_id]}
    }
    DynamicSupervisor.start_child(__MODULE__, child_spec)
  end
end

# --- Application Entry Point --- (Simulated)
{:ok, _registry_pid} = MyApp.SessionsRegistry.start_link([])
{:ok, _supervisor_pid} = MyApp.SessionSupervisor.start_link([])

# Start a session for user_101
{:ok, session_pid_1} = MyApp.SessionSupervisor.start_session(:user_101)
IO.puts("Session 1 PID: #{inspect(session_pid_1)}")

# Start a session for user_102
{:ok, session_pid_2} = MyApp.SessionSupervisor.start_session(:user_102)
IO.puts("Session 2 PID: #{inspect(session_pid_2)}")

# Look up user_101's session via Registry
{:ok, [pid_from_registry]} = Registry.lookup(MyApp.SessionsRegistry, :user_101)
IO.puts("Found user_101 session PID via Registry: #{inspect(pid_from_registry)}")
IO.puts("User ID from session: #{MyApp.UserSession.get_user_id(pid_from_registry)}")

Dynamic & Registry Quiz

Consider an application that uses DynamicSupervisor to manage user sessions and Registry to look up sessions by user ID. What is the primary benefit of using Registry in this scenario?

Jawab di pelajaran interaktif

Recap: Dynamic & Registry

You've mastered dynamic process management!

DynamicSupervisor allows you to start and stop child processes on demand, making your application highly flexible and adaptable.
The Registry module provides a powerful key-value store for associating processes with meaningful names or IDs, enabling reliable lookup of dynamically started processes.

By combining these two, you can build robust, scalable applications that manage their resources efficiently.

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Apakah pelajaran “Supervisor Dinamis dan Registry” gratis?

Ya — teks lengkap “Supervisor Dinamis dan Registry” gratis dibaca di sini di web. Untuk praktiknya secara interaktif (editor kode bawaan dan tutor AI 24/7) dan buka sisa kursus Elixir & Phoenix: Scalable Backend Development, upgrade ke CoddyKit PRO. Kursus Elixir & Phoenix: Scalable Backend Development mencakup 4 pelajaran total.

Apa yang akan aku pelajari di “Supervisor Dinamis dan Registry”?

Pelajari cara memulai dan menghentikan proses secara dinamis dengan `DynamicSupervisor` serta menggunakan `Registry` untuk mencari proses. Kamu berlatih Elixir & Phoenix: Scalable Backend Development dengan kode praktik yang langsung kamu jalankan di browser, dan tutor AI 24/7 menjawab pertanyaanmu saat kamu mengerjakan pelajaran ini.

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