From: Jatin Kumar <jatinkumar.nitk@...>
Date: 2010-08-03T21:56:48+09:00
Subject: Re: Standard IO streams in Ruby


>> In my rails controller, I am doing the following :
>> 
>> @output = `g++ j.cpp -o "prog" && ./prog`
> 
> Why are you compiling it every time?

I am not compiling it every time, only when the user clicks on the 
compile/execute button that i provide in the view.

> From some of your questions, it seems like you're going to let the user 
> enter
> source code, then compile it and run it. Is that true? If so, do you 
> realize
> how insanely dangerous that is?

Yes, I am exactly doing that. Why does it sound to you insanely 
dangerous??
Could you elaborate a little on that.?

>> If the user has to give input, I open a dialog box on the view with a
>> textfield where he/she can enter the input, and the program continues to
>> execute.
> 
> You can't do that from inside a Rails controller. You can capture IO 
> with
> popen or open3:
> 
> http://www.ensta.fr/~diam/ruby/online/ruby-doc-
> stdlib/libdoc/open3/rdoc/classes/Open3.html
> 

Yes, i know that I have to capture IO for that. Thanks for the link. 
Really appreciated.

> But that doesn't solve your problem by itself -- you need to send data 
> to and
> from the browser interactively. That means you at least need AJAX, and
> possibly Comet or Web Sockets, combined with some sort of background
> processing.

Yes, I am using AJAX. I will look into Comet or Web Sockets, but I have 
no idea of a web socket and how do they work? How can I use them in 
here?

>> I tried doing this :
>> 
>> @output = `g++ j.cpp -o "prog" && ./prog| tee prog`
> 
> That would overwrite your program with the output of your program. Is 
> that
> really what you want to do?
> 
> man tee
> 
No, I am not overwriting the program with the output. There's probably 
something wrong but i can take care of it.

>> In short, how can I get control of stdin, so that whenever the stdin
>> waits for some user input, i get to know that it is waiting for the user
>> input
> 
> You can't do that either, not really. The best you can do is always 
> provide
> that text field, and show the user standard output and standard error, 
> so they
> can see the program prompting them -- and detect the program exiting, so 
> you
> can remove the text field.

Got your point.

> If you want to be able to do this efficiently, you're going to need to 
> do a
> lot of reading. It basically boils down to these two options:
> 
> http://en.wikipedia.org/wiki/Comet_(programming)
> http://www.websockets.org/

> But however you implement the updates -- you could always just poll -- 
> but
> you're still going to need one of these:
> 
> http://www.tobinharris.com/past/2009/3/9/6-ways-to-run-background-jobs-in-
> rubyonrails/

Thanks for the links. I will read them all and will get back to you if i 
need help.


> There are probably newer/better alternatives to those, too...
Newer / Better alternatives ??? I could not think of a better way. If 
you have something in your mind that can ease the above process, that 
would be great.
Thanks for all your help.

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