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| Guest |
 Posted: Fri Sep 16, 2011 8:39 am |
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Guest
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Hi,
I am a newbie of Erlang, here I have a question for receive
message in Erlang loop.
Like below Erlang code, when process receive one message, it will
invoke loop again,
then it can service like a server, receive message forever.
BUT is possible that process will stack overflow after receive too
many message? the process invoke loop again and again.
I saw there have many code write like this in <<Programming Erlang>> book.
loop() ->
receive
hello ->
io:format("hello\n"),
loop();
Other ->
io:format("I don't know what is this message, ~p is ~n" ,[Other]),
loop()
end.
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| Guest |
| Posted: Fri Sep 16, 2011 8:44 am |
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Guest
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On Fri, Sep 16, 2011 at 9:38 AM, Jovi Zhang <bookjovi@gmail.com (bookjovi@gmail.com)> wrote:
Quote: Hi,
I am a newbie of Erlang, here I have a question for receive
message in Erlang loop.
Like below Erlang code, when process receive one message, it will
invoke loop again,
then it can service like a server, receive message forever.
BUT is possible that process will stack overflow after receive too
many message? the process invoke loop again and again.
I saw there have many code write like this in <<Programming Erlang>> book.
loop() ->
receive
hello ->
io:format("hello\n"),
loop();
Other ->
io:format("I don't know what is this message, ~p is ~n" ,[Other]),
loop()
end.
No stack overflow, due to tail call optimisation. See also http://www.erlang.org/doc/reference_manual/functions.html#id74170
Robby
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| Guest |
| Posted: Fri Sep 16, 2011 8:57 am |
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Guest
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On Fri, Sep 16, 2011 at 4:44 PM, Robert Raschke <rtrlists@googlemail.com> wrote:
>
> On Fri, Sep 16, 2011 at 9:38 AM, Jovi Zhang <bookjovi@gmail.com> wrote:
>>
>> Hi,
>> I am a newbie of Erlang, here I have a question for receive
>> message in Erlang loop.
>> Like below Erlang code, when process receive one message, it will
>> invoke loop again,
>> then it can service like a server, receive message forever.
>> BUT is possible that process will stack overflow after receive too
>> many message? the process invoke loop again and again.
>>
>> I saw there have many code write like this in <<Programming Erlang>>
>> book.
>>
>> loop() ->
>> receive
>> hello ->
>> io:format("hello\n"),
>> loop();
>> Other ->
>> io:format("I don't know what is this message, ~p is ~n"
>> ,[Other]),
>> loop()
>> end.
>>
>
> No stack overflow, due to tail call optimisation. See also
> http://www.erlang.org/doc/reference_manual/functions.html#id74170
>
> Robby
>
Thanks, but when I test it using escript, the result is like below,
"loop end" printed two times, it means it stacked!
[root@localhost Erlang]# cat jovi.erl
#!/usr/bin/env escript
loop() ->
receive
one ->
io:format("one\n"),
loop();
two ->
io:format("two\n")
end,
io:format("loop end\n").
main(_) ->
Pid = spawn(fun() -> loop() end),
Pid ! one,
Pid ! two,
receive
_Any -> void
end.
[root@localhost Erlang]# ./jovi.erl
one
two
loop end
loop end
^C
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| Guest |
| Posted: Fri Sep 16, 2011 9:05 am |
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Guest
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Your last call to io:format/2 is making the function non tail recursive.
/H |
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| Guest |
| Posted: Fri Sep 16, 2011 9:06 am |
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Guest
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| You might find this link useful as well |
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| Guest |
| Posted: Fri Sep 16, 2011 9:45 am |
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Guest
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On Fri, Sep 16, 2011 at 5:06 PM, Steve Strong <steve@srstrong.com> wrote:
> You might find this link useful as
> well http://en.wikipedia.org/wiki/Tail_call - the reason that your new
> example is stacking is that having code after the recursion means that it's
> no longer tail-recursive, and will indeed consume stack space.
> --
> Steve Strong
> @srstrong
> Sent with Sparrow
>
> On Friday, 16 September 2011 at 10:57, Jovi Zhang wrote:
>
> On Fri, Sep 16, 2011 at 4:44 PM, Robert Raschke <rtrlists@googlemail.com>
> wrote:
>
> On Fri, Sep 16, 2011 at 9:38 AM, Jovi Zhang <bookjovi@gmail.com> wrote:
>
> Hi,
> I am a newbie of Erlang, here I have a question for receive
> message in Erlang loop.
> Like below Erlang code, when process receive one message, it will
> invoke loop again,
> then it can service like a server, receive message forever.
> BUT is possible that process will stack overflow after receive too
> many message? the process invoke loop again and again.
>
> I saw there have many code write like this in <<Programming Erlang>>
> book.
>
> loop() ->
> receive
> hello ->
> io:format("hello\n"),
> loop();
> Other ->
> io:format("I don't know what is this message, ~p is ~n"
> ,[Other]),
> loop()
> end.
>
> No stack overflow, due to tail call optimisation. See also
> http://www.erlang.org/doc/reference_manual/functions.html#id74170
>
> Robby
>
> Thanks, but when I test it using escript, the result is like below,
> "loop end" printed two times, it means it stacked!
>
> [root@localhost Erlang]# cat jovi.erl
> #!/usr/bin/env escript
>
> loop() ->
> receive
> one ->
> io:format("one\n"),
> loop();
> two ->
> io:format("two\n")
> end,
> io:format("loop end\n").
>
>
> main(_) ->
> Pid = spawn(fun() -> loop() end),
> Pid ! one,
> Pid ! two,
> receive
> _Any -> void
> end.
>
>
> [root@localhost Erlang]# ./jovi.erl
> one
> two
> loop end
> loop end
> ^C
> _______________________________________________
> erlang-questions mailing list
> erlang-questions@erlang.org
> http://erlang.org/mailman/listinfo/erlang-questions
>
>
Hmm, Thanks very much, I understand it now!
.jovi
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| Guest |
| Posted: Fri Sep 16, 2011 3:31 pm |
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Guest
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On Fri, Sep 16, 2011 at 11:45, Jovi Zhang <bookjovi@gmail.com> wrote:
>
> Hmm, Thanks very much, I understand it now!
>
Let me add that the perhaps most subtle way to make a function
stacking is to put an exception handler on the stack. Beware of that
case if you wonder why something is stacking when it should not be. It
only happens if the exception handler is pushed by each recursive call
though.
--
J.
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