Show information on web-page from external process in n2o framework

Question

How can I show information from external processes in N2O framefork.

Code like this:

tokyoWeather() ->
     timer:sleep(10000),
     Data = getTokyoWeater(),
     ??? SHOW_ON_PAGES,
     tokyoWeather().
lisbonWeather() ->
     timer:sleep(10000),
     Data = getLisbonWeater(),
     ??? SHOW_ON_PAGES,
     lisbonWeather().

Page1:

body() ->
    [ #panel { id=TokyoWeather text= <<>> },
      #panel { id=LisbonWeather, text= <<>> },
      ...].

Page2:

body() ->
    [ #panel { id=TokyoWeather text= <<>> },
      #panel { id=LisbonWeather, text= <<>> },
      ...].

Thanks in advance.

Answer 1

Use wf:reg and wf:flush functions. Example: /samples/apps/review/src/index.erl

1. Register unique name for a page-process:

   23: event(init) -> wf:reg(room)...

2. Updating DOM:

   60: wf:insert_bottom(history, Terms)

3. Flushing changes to browser using page-process name:

   62: wf:flush(room)

Answer 2

Documentation suggests using wf:reg/1 and wf:flush. However, this requires you to register process into a pool, which is handy for when you want to manipulate multiple processes at once, but quite redundant otherwise.

Another interesting function the N2O book mentions is wf:flush/1. Its description claims that it does something completely different from wf:flush/0, while in reality it does not. It really just collects the wf actions placed into a "buffer" and sends them via wf:send/2 to a registered supposedly websocket processes. Meanwhile the websocket process sits in a timed receive loop.

After some N2O's code inspection, there is a pretty simple solution, in my opinion:

1. Starting at process that can render actions(e.g. the websocket process), spawn your desired function and pass the parent process id as one of its parameters

   async_render() ->
     Pid = self(),
     spawn(fun() -> update(Pid) end).
   

2. Perform your wf actions in now asynchronous function, then retrieve the queued actions, clear the buffer, and finally send the a tuple of {flush, Actions} to your parent process.

   update(Pid) ->
     %% Your wf:insert..., update, etc. code here
     Actions = wf:actions(),
     wf:actions([]),
     Pid ! {flush, Actions}.
   

The rest is done by N2O for you :)