[erlang-questions] Question re console io in a distributed computation

[Ulf Wiger]

Well, I'm not quite sure why it didn't work with the group leader
(I'd have to dig into that), but the 'user' trick ought to work with
the question as well. Compare:

rpc:call(OtherNode, io, get_line, ["Hello? "])

with

rpc:call(OtherNode, io, get_line, [user, "Hello? "]).

The first version should give a prompt on the originating node,
and the second version should give it on the target node
(assuming, of course, that the target node has a shell.)

BR,
Ulf W

2008/10/29 David Cabana <drcabana@REDACTED>:
> I've now played with both of  Ulf's suggested approaches  (using
> io:format(user, Fmt, Args), or alternatively, resetting processes group
> leaders) and have gotten output to go the correct consoles with both
> approaches.  Which of course led to the next hurdle,  reading input from the
> player console.
>
> The referee sent a question to the player, which was written to the player
> node's console. What I want to do is type a response in the player console,
> have it read, parsed, and sent to the referee, but so far no luck. My
> responses vanish into the ether, and the referee hangs waiting for players
> to respond.
>
> Here is how I am trying to respond. When the player process receives a
> question, it writes to the console and tries to read a line:
>
> <when I have reset player group leaders>
>     io:fwrite("~n~s", [Question]),
>     Reply = io:get_line(["= "]),
>
> <did not mess with group leaders, instead specified the 'user' atom during
> io>
> I have also tried:
>     io:fwrite(user, "~n~s", [Question]),
>     Reply = io:get_line(user, ["= "]),
>
>
> It occurs to me that maybe I am going about this the wrong way? Perhaps my
> approch is misconceived.  I have to believe that console IO in a
> client-server setting is pretty common. Can anyone point me in the right
> direction?
>
> Thank you,
> David
>>
>> On Fri, Oct 24, 2008 at 2:44 PM, Ulf Wiger (TN/EAB)
>> <ulf.wiger@REDACTED> wrote:
>>>
>>> David Cabana skrev:
>>> >
>>>>
>>>> The messages flow correctly, but all the terminal io happens in
>>>> a single console, the one associated with the referee node.
>>>>
>>>> My question is how to get player output written to the console of the
>>>> corresponding
>>>> player node?
>>>
>>> Use io:format(user, Fmt, Args)
>>>
>>> Alternatively, set the group leader of the process to some
>>> local process - e.g. the group leader of net_kernel
>>> (found by calling process_info(whereis(net_kernel),group_leader)).
>>>
>>> The group leader is the process that's handed all io messages.
>>> The rpc server deliberately sets the group leader of an rpc
>>> handler process to that of the caller on the originating node,
>>> since the remote node may not always have a tty to print to.
>>> When spawning, the group leader of the spawned process will
>>> be inherited from the parent. If you spawn a process on
>>> another node, it will still have the same group leader as
>>> the parent.
>>>
>>> The BIF group_leader(Pid,New_group_leader_pid) sets a new
>>> leader.
>>>
>>> BR,
>>> Ulf W
>>
>
>
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