erlang send 原语简单使用

来自 ：

-module(tut15).
-export([start/0, ping/2, pong/0]).

ping(0, Pong_PID) ->
    Pong_PID ! finished,
    io:format("ping finished~n", []);
ping(N, Pong_PID) ->
    Pong_PID ! {ping, self()},
    receive
        pong ->
            io:format("Ping received pong~n", [])
    end,
    ping(N - 1, Pong_PID).


pong() ->
    receive
        finished ->
            io:format("Pong finished~n", []);
        {ping, Ping_PID} ->
            io:format("Pong received ping~n", []),
            Ping_PID ! pong,
            pong()
    end.

start() ->
    Pong_PID = spawn(tut15, pong, []),
    spawn(tut15, ping, [3, Pong_PID]).

首先理解为递归，上面的代码 严格按 匹配模式来运行；遇到 receive 原语会拥塞；

ping > Pong received ping
  pong > Ping received pong
  ping N-1 
  ping > Pong received ping
    pong > Ping received pong
    ping N-1-1
    ping > Pong received ping
       pong > Ping received pong
       ping N-1-1  （触发 ping(0, Pong_PID) ）
       ping > ping finished
           Pong finished