0

我写了以下代码：

-module(ring).

-export([start/3]).

start(1, 1, Message) -> %special case, no new processes to be launched
    io:format(" Start/3, branch 1~n~n"),
    loop(self(), 1, 1),
    self() ! Message,
    self() ! {self(), quit};
start(1, MsgNum, Message) when MsgNum > 1 -> %first process, register self, launch next, send message, loop
    io:format(" Start/3 branch 2, ProcNum: ~b, MsgNum: ~b, process: ~p~n~n", [1, MsgNum, self()]),
    register(process_1, self()),
    self() ! {self(), Message},
    NextPid = spawn(ring, start, [2, MsgNum, Message]),
    NextPid ! {self(), Message},
    loop(NextPid, 1, MsgNum);
start(MsgNum, MsgNum, _) when MsgNum >= 1 ->    %last process, don't start new process, quit master, run loop
    io:format(" Start/3 branch 3, MsgNum = ProcNum = ~b, process: ~p~n~n", [MsgNum, self()]),
    process_1 ! {self(), quit},
    loop(process_1, MsgNum, MsgNum);
start(ProcNum, MsgNum, Message) when ProcNum >= 1 -> %everything else, start next process, send it a message, start loop
    io:format(" Start/3 branch 4, ProcNum: ~b, MsgNum: ~b, process: ~p~n~n", [ProcNum, MsgNum, self()]),
    NextPid = spawn(ring, start, [ProcNum + 1, MsgNum, Message]),
    NextPid ! {self(), Message},
    loop(NextPid, ProcNum, MsgNum).

loop(NextPid, ProcNum, MsgNum) ->
    receive
        {Sender, quit} -> % send quit to next process in queue, then terminate with 'ok'
        io:format(" Sender: ~p  Quitting process ~p Next: ~p~n~n", [Sender, self(), NextPid]),
        NextPid ! {self(), quit},
        ok; 
    {Sender, Msg} -> % print message and wait for next message
        io:format(" Message: ~w~n  procNum: ~b msgNum: ~b sender: ~p self: ~p  next: ~p~n~n", [Msg, ProcNum, MsgNum, Sender, self(), NextPid]),
        loop(NextPid, ProcNum, MsgNum); 
    _ ->  %flush garbage, should never get here...
        io:format(" Oops. Received someting unexpected")
    end.

我希望这段代码能够启动一系列进程，每个进程都应该打印一条消息，然后礼貌地退出。例如，如果我运行 ring:start(1,3,hola)，我希望看到三个进程、三个消息和三个退出。它几乎可以正常工作，只是初始进程没有终止，正如在这个 shell 会话中看到的那样：

Eshell V5.10.1  (abort with ^G)
1> c(ring).
{ok,ring}
2> processes().
[<0.0.0>,<0.3.0>,<0.6.0>,<0.7.0>,<0.9.0>,<0.10.0>,<0.11.0>,
 <0.12.0>,<0.13.0>,<0.14.0>,<0.15.0>,<0.16.0>,<0.17.0>,
 <0.18.0>,<0.19.0>,<0.20.0>,<0.21.0>,<0.22.0>,<0.23.0>,
 <0.24.0>,<0.25.0>,<0.26.0>,<0.27.0>,<0.28.0>,<0.32.0>]
3> ring:start(1,3,hola).
 Start/3 branch 2, ProcNum: 1, MsgNum: 3, process: <0.32.0>

 Message: hola
  procNum: 1 msgNum: 3 sender: <0.32.0> self: <0.32.0>  next: <0.41.0>

 Start/3 branch 4, ProcNum: 2, MsgNum: 3, process: <0.41.0>

 Message: hola
  procNum: 2 msgNum: 3 sender: <0.32.0> self: <0.41.0>  next: <0.42.0>

 Start/3 branch 3, MsgNum = ProcNum = 3, process: <0.42.0>

 Message: hola
  procNum: 3 msgNum: 3 sender: <0.41.0> self: <0.42.0>  next: process_1

 Sender: <0.42.0>  Quitting process <0.32.0> Next: <0.41.0>

 Sender: <0.32.0>  Quitting process <0.41.0> Next: <0.42.0>

 Sender: <0.41.0>  Quitting process <0.42.0> Next: process_1

ok
4> processes().
[<0.0.0>,<0.3.0>,<0.6.0>,<0.7.0>,<0.9.0>,<0.10.0>,<0.11.0>,
 <0.12.0>,<0.13.0>,<0.14.0>,<0.15.0>,<0.16.0>,<0.17.0>,
 <0.18.0>,<0.19.0>,<0.20.0>,<0.21.0>,<0.22.0>,<0.23.0>,
 <0.24.0>,<0.25.0>,<0.26.0>,<0.27.0>,<0.28.0>,<0.32.0>]

我为长代码/日志块道歉，但我认为这很清楚 start/3 会导致启动三个进程（<0.32.0>、<0.41.0> 和 <0.42.0>），并且每个都打印一条消息，并且每个都收到它的退出消息。但是，当一切都完成后，初始进程 (<0.32.0>) 仍在运行。我的理解是，一旦没有更多代码要运行，该进程就应该终止——第一个进程有什么特别之处可以阻止它的终止吗？

提前致谢。

4

1 回答 1

4

您的函数 start/3 不会启动您称为“初始”的过程。相反，该函数在已经存在的进程中运行。这是 erlang shell 的过程，你正在使用它。它有 pid <0.32.0>。仔细查看函数 processes() 的第一次调用的输出：

2> processes().
[<0.0.0>,<0.3.0>,<0.6.0>,<0.7.0>,<0.9.0>,<0.10.0>,<0.11.0>,
 <0.12.0>,<0.13.0>,<0.14.0>,<0.15.0>,<0.16.0>,<0.17.0>,
 <0.18.0>,<0.19.0>,<0.20.0>,<0.21.0>,<0.22.0>,<0.23.0>,
 <0.24.0>,<0.25.0>,<0.26.0>,<0.27.0>,<0.28.0>,<0.32.0>]

列表中的最后一个 pid 是 <0.32.0>。因此，当您调用 start/3 时，它会在该进程中运行，并且当它退出循环时，进程 <0.32.0> 将不会完成 - 它只会返回到 erlang shell 并等待下一个命令。

于 2013-04-30T05:47:40.250 回答