elixir - 当 worker 重新启动时，主管保持状态

Question

我有一个 AgentTest 作为保持状态的工作人员，还有一个 Supv 作为监视器 AgentTest

 defmodule AgentTest do
  use Agent

  def start_link(state) do
    Agent.start_link(fn -> state end, name: :test) 
  end

  def incr do
    Agent.get_and_update(:test, fn state -> {state, state + 1} end) 
  end

  def crash do
    Agent.stop(:test, :crash) 
  end

  def get do
    Agent.get(:test, fn state -> state end) 
  end
end

defmodule Supv do
  use Supervisor

  def start_link do
    Supervisor.start_link(Supv, []) 
  end

  def init(_arg) do
    Supervisor.init([
      {AgentTest, 1} 
    ], strategy: :one_for_one) 
  end
end

我在iex中尝试过，重启后状态不再保留:

iex(2)> Supv.start_link
{:ok, #PID<0.99.0>}
iex(3)> AgentTest.incr
1
iex(4)> AgentTest.incr
2
iex(5)> AgentTest.get
3
iex(6)> AgentTest.get
3
iex(7)> AgentTest.crash
:ok
iex(8)>
10:03:26.560 [error] GenServer :test terminating
** (stop) :crash
Last message: []
State: 3

nil
iex(9)> AgentTest.get
1

Supv重启时如何保持AgentTest状态？

我使用的是 Elixir 1.5

Answer 1

为了保留状态，您可以运行一个单独的进程，该进程将存储一个隐藏值。

defmodule Supv do
  use Supervisor

  def start_link do
    children = [
      worker(Stash, [1]),
      worker(AgentTest, [])
    ]

    Supervisor.start_link(Supv, children)
  end

  def init(children) do
    supervise children, strategy: :one_for_one
  end
end

当主 AgentTest 进程终止时，它将其当前值放入存储中。当进程重新启动时，它会从存储中获取值:

defmodule AgentTest do
  use Agent

  def start_link do
    Agent.start_link(fn -> Stash.get() end, name: :test)
  end

  def incr do
    Agent.get_and_update(:test, fn state -> {state, state + 1} end)
  end

  def crash do
    Stash.update(get())

    Agent.stop(:test, :crash)
  end

  def get do
    Agent.get(:test, fn state -> state end)
  end
end

存储过程可以是一个简单的代理:

defmodule Stash do
  use Agent

  def start_link(initial_number) do
    Agent.start_link(fn -> initial_number end, name: :stash)
  end

  def get do
    Agent.get(:stash, fn state -> state end)
  end

  def update(number) do
    Agent.update(:stash, fn _ -> number end)
  end
end

为了简化示例，我将进程命名为 (:stash)，但它的 pid 当然可以作为参数传递给 AgentTest .