[erlang-questions] processes spawned on remote nodes don't run

[Dániel Szoboszlay]

Do you have the same version of user_default on all the nodes? You try to
execute a local fun remotely, it will only work if you have exactly the
same version of the beams on all the nodes.

Cheers,
Daniel

On Tue, 6 Dec 2016 at 11:35 Khitai Pang <khitai.pang@REDACTED> wrote:

> Hi Adrian,
>
> Thank you for the information but unfortunately it's not the cause of my
> problem.  If I add 'user' io:format():
>
> (myapp@REDACTED)6> run_on_all_nodes().
> [<27616.12396.0>,<27612.19603.39>,<27615.48.51>]
>
> (myapp@REDACTED)7> [spawn(Node, fun() -> io:format(user, "This runs on
> ~p~n", [node()]) end) || Node <- nodes()].
> [<27616.12397.0>,<27612.19600.39>,<27615.77.51>]
>
> (myapp@REDACTED)8> [spawn(Node, fun() -> io:format("This runs on ~p~n",
> [node()]) end) || Node <- nodes()].
>
> This runs on myapp@REDACTED
> This runs on rabbit@REDACTED
> This runs on rabbit@REDACTED
> [<27616.12398.0>,<27612.19631.39>,<27615.89.51>]
>
> It doesn't seem to be I/O channeling problem, it seems that the spawned
> processes just don't run...
>
>
> Thanks
>
> khitai
>
>
> On 2016/12/6 17:52, Adrian Roe wrote:
>
> This confused me for a while as well…
>
> To quote http://erlang.org/doc/man/erlang.html
>
> group_leader() -> pid()
>
> Returns the process identifier of the group leader for the process
> evaluating the function.
>
> Every process is a member of some process group and all groups have a *group
> leader*. All I/O from the group is channeled to the group leader. When a
> new process is spawned, it gets the same group leader as the spawning
> process. Initially, at system startup, init is both its own group leader
> and the group leader of all processes.
> There’s a helpful post here
> <http://erlang.org/pipermail/erlang-questions/2008-April/034573.html>
> http://erlang.org/pipermail/erlang-questions/2008-April/034573.html that
> talks about exactly what you are seeing.
>
> If you change the
> io:format("This runs on ~p~n", [node()])
> to
> io:format(user, "This runs on ~p~n", [node()])
>
> I strongly suspect you will see the output you were expecting…
>
> Adrian
>
> On 6 Dec 2016, at 09:34, Khitai Pang < <khitai.pang@REDACTED>
> khitai.pang@REDACTED> wrote:
>
> Hi,
>
> I have the following function in user_default.erl:
>
> run_on_all_nodes() ->
>     [spawn(Node, fun() ->
>                          io:format("This runs on ~p~n", [node()])
>                  end) || Node <- nodes()].
>
> When I run this function, processes can be spawned on remote nodes but
> it seems that they don't run:
>
> (myapp@REDACTED)1> nodes().
> [myapp@REDACTED,rabbit@REDACTED,rabbit@REDACTED]
>
> (myapp@REDACTED)2> run_on_all_nodes().
> [<27616.12336.0>,<27612.15341.39>,<27615.22399.50>]
>
> If I manually run the spawn command in the attached shell, it all works
> fine:
>
> (myapp@REDACTED)3> [spawn(Node, fun() -> io:format("This runs on ~p~n",
> [node()]) end) || Node <- nodes()].
> This runs on myapp@REDACTED
> This runs on rabbit@REDACTED
> This runs on rabbit@REDACTED
> [<27616.12339.0>,<27612.15569.39>,<27615.22640.50>]
>
>
> Any idea?
>
>
> Thanks
> Khitai
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