Question

我试图了解这段Elixir代码中发生了什么。我们生成了两个进程，然后生成的进程将消息回送给发送方，但我只在iex中看到一条消息。怎么了？

<html>
 <head></head>
 <body>
  <?php include 'file.php';?>
  <form action="" method="POST">
   <b>Busque Jรก</b>
   <input type="text" name="prestador" placeholder="prestador">
   <input type="text" name="cidade" placeholder="cidade">
   <input type="submit">
  </form>
 </body>
</html>

iex中的输出总是＆＃34; Hello Bob＆＃34;

defmodule TwoPs do
  # a simple echo function - take a pid to send message back to
  def echo(pid) do
    #wait till the spawned process receives a message, turn around and echo it back to the sender
    receive do
      msg ->
        IO.puts("Received #{msg}")
        send pid, {:ok, "Hello #{msg}"}
    end
  end

  #spawn's two processes and sends a message to both...expects an echo back from both spawned processes
  def create_ps() do
    #spawn the two processes
    p1 = spawn(TwoPs, :echo, [self])
    p2 = spawn(TwoPs, :echo, [self])

    #send a message to the first pid
    send p1, "World"

    #receive message back from spawned child 1
    receive do
      {:ok, msg} -> "#{msg}"
    end

    #send a message to the second pid
    send p2, "Bob"

    #receive message from the spawned child 2
    receive do
      {:ok, msg} -> "#{msg}"
    end

  end

end

为什么我们不看＆＃34; Hello World＆＃34;？

Answer 1

您看到的值是TwoPs.create_ps/0的返回值，在这种情况下是第二个接收块返回的值。如果要打印两个接收的值，则应使用IO.puts/2：

明确打印它们

defmodule TwoPs do
  def echo(pid) do
    receive do
      msg ->
        IO.puts("Received #{msg}")
        send pid, {:ok, "Hello #{msg}"}
    end
  end

  def create_ps() do
    p1 = spawn(TwoPs, :echo, [self])
    p2 = spawn(TwoPs, :echo, [self])

    send p1, "World"
    receive do
      {:ok, msg} -> IO.puts "#{msg}"
    end

    send p2, "Bob"
    receive do
      {:ok, msg} -> IO.puts "#{msg}"
    end
  end
end

测试：

iex(1)> TwoPs.create_ps
Received World
Hello World
Received Bob
Hello Bob
:ok

为什么发件人没有再次收到生成的流程消息？

1 个答案: