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我创建了一个非常基本的 Elixir 主管和工作人员，以测试 Erlang VM 的热代码重载功能。这是主管：

defmodule RelTest do
  use Application

  # See http://elixir-lang.org/docs/stable/elixir/Application.html
  # for more information on OTP Applications
  def start(_type, _args) do
    import Supervisor.Spec, warn: false

    port = Application.get_env(:APP_NAME, :listen_port, 9000)
    {:ok, socket} = :gen_tcp.listen(port, [:binary, active: false, reuseaddr: true])

    # Define workers and child supervisors to be supervised
    children = [
      # Starts a worker by calling: RelTest.Worker.start_link(arg1, arg2, arg3)
      # worker(RelTest.Worker, [arg1, arg2, arg3]),
      worker(Task, [fn -> TestListener.start(socket) end])
    ]

    # See http://elixir-lang.org/docs/stable/elixir/Supervisor.html
    # for other strategies and supported options
    opts = [strategy: :one_for_one, name: RelTest.Supervisor]
    Supervisor.start_link(children, opts)
  end
end

基本上，我正在启动一个任务工作者，即：

defmodule TestListener do
  require Logger

  def start(socket) do
    {:ok, client} = :gen_tcp.accept(socket)
    Logger.info "A client connected"
    Task.async(fn -> loop(client) end)
    start(socket)
  end

  def loop(socket) do
    case :gen_tcp.recv(socket, 0) do
      {:ok, _} ->
    say_hello(socket)
    Logger.info "Said hello to client ;)"
    loop(socket)
      {:error, _} ->
    Logger.info "Oops, client had error :("
    :gen_tcp.close(socket)
    end
  end

  def say_hello(socket) do
    :ok = :gen_tcp.send(socket, <<"Hey there!\n">>)
  end

end

这是版本0.1.0。所以我运行这些：

MIX_ENV=prod mix compile
Mix_ENV=prod mix release

我得到了一个很好的释放。我运行它，./rel/rel_test/bin/rel_test console一切正常。现在我要修改代码和版本，所以这里是0.1.1监听器的版本：

defmodule TestListener do
  require Logger

  def start(socket) do
    {:ok, client} = :gen_tcp.accept(socket)
    Logger.info "A client connected"
    Task.async(fn -> loop(client) end)
    start(socket)
  end

  def loop(socket) do
    case :gen_tcp.recv(socket, 0) do
      {:ok, _} ->
    say_hello(socket)
    Logger.info "Said hello to client ;)"
    loop(socket)
      {:error, _} ->
    Logger.info "Oops, client had error :("
    :gen_tcp.close(socket)
    end
  end

  def say_hello(socket) do
    :ok = :gen_tcp.send(socket, <<"Hey there, next version!\n">>)
  end

end

现在我跑

MIX_ENV=prod mix compile
Mix_ENV=prod mix release

并appup创建成功，然后进行热升级

./rel/rel_test/bin/rel_test upgrade "0.1.1"

并且升级有效，但升级后它会杀死我的听众。

我用一个nc localhost 9000（9000 是监听器的端口）进行了测试，保持连接并运行升级命令。连接被终止，我在控制台中收到一条消息：

=SUPERVISOR REPORT==== 31-Aug-2016::23:40:09 ===
     Supervisor: {local,'Elixir.RelTest.Supervisor'}
     Context:    child_terminated
     Reason:     killed
     Offender:   [{pid,<0.601.0>},
                  {id,'Elixir.Task'},
                  {mfargs,
                      {'Elixir.Task',start_link,
                          [#Fun<Elixir.RelTest.0.117418367>]}},
                  {restart_type,permanent},
                  {shutdown,5000},
                  {child_type,worker}]

那么为什么会发生这种情况呢？是我缺少的东西，还是预期的行为？不就是热代码重载的用例吗？

我读过LYSE，但作者说运行代码应该继续运行，只有升级后进行的外部调用才能使用新版本。

那为什么要杀工人？

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