Elixir进程未收到消息 [英] Elixir process not receiving message

问题描述

我是Elixir的新手，目前正在学习有关过程的知识。在实践中，我编写了一个ping pong程序，该程序从2个进程中打印 ping和 pong。收到1或2条消息后，进程总是死机。这是我的代码

I am new to Elixir and currentlly learning about process. In a practice I wrote a ping pong program that prints "ping" and "pong" from 2 processes. The processes always dead after receiving 1 or 2 messages. Here is my code

defmodule Pingpong do
  def play do
    receive do
     {sender, :ping} ->
        IO.puts  "ping"
        send sender, {self, :pong}
        play
     {sender, :pong} ->
       IO.puts  "pong"
       send sender, {self, :ping}
       play
   end
  end

  def start() do
    a = spawn(Pingpong, :play, [])
    b = spawn(Pingpong, :play, [])
    send a, {b, :ping}
  end
end

有时候我只有一行输出

$ elixir -r pingpong.exs -e "Pingpong.start"
> ping

或多行，然后停止

ping
pong
ping
pong
ping
pong

但是我认为它应该连续打印输出，直到我停止程序为止。
上面的代码可能出什么问题？

But I think it should continuously print outputs until I stop the program. What could go wrong with the above code?

推荐答案

这是因为Erlang VM在执行<$ c之后退出$ c> Pingpong.start ，因为主进程没有任何代码可执行。如果添加：timer.sleep（：infinity）以确保主进程没有退出，则应该看到 ping 和 pong 会永远连续打印：

This is because the Erlang VM exits after executing Pingpong.start as the main process doesn't have any code left to execute. If you add :timer.sleep(:infinity) to make sure the main process doesn't exit, you should see ping and pong being printed continuously forever:

$ elixir -r pingpong.exs -e "Pingpong.start; :timer.sleep(:infinity)"

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