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djberg96 (2603)

djberg96
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Journal of djberg96 (2603)

Thursday October 28, 2004

11:49 PM

Forgive me Father, for I have used "goto"

[ #21581 ]

Well, it took 7 years, but I finally found a use for "goto" outside of BASIC. In my particular case, it was within a Ruby C extension. I wanted to create 'tail -f' functionality for monitoring the Windows event log. It makes sense when you take blocks into consideration. To wit:

e = EventLog.open("Application") e.tail{ |rec| puts "Record added to log" p rec }

The tail method sits in an infinite loop (which is accomplished with the 'goto'), yielding a (custom) struct every time a record is written to the event log.

On a stranger note, the Windows function NotifyChangeEventLog() can only detect a maximum of one change every five seconds. That means, even if 20 records were written to the event log in under 5 seconds, that block would only pick up the first one. No, there's no way around it.

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Forgive me Father, for I have used "goto" More | Login | Reply

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I don't see the goto (Score:1)

by btilly (5037)

You aren't showing the code where you felt it necessary to use a goto, so I cannot judge its validity. I suspect that it isn't needed though.
For the record, I know of exactly two necessary uses of goto in Perl.
- Re:I don't see the goto (Score:2)
  
  by djberg96 (2603)
  
  static VALUE eventlog_tail(VALUE self){ ELS* ptr; VALUE rbBlock, rbSource, rbServer; HANDLE hEvent; DWORD dwWaitResult; int rv; Data_Get_Struct(self,ELS,ptr); eventblock: hEvent = CreateEvent( NULL, // default security attributes FALSE, // no manual reset FALSE, // create as not signaled NULL
  - Re:I don't see the goto (Score:1)
    
    by btilly (5037)
    
    First of all that is written in C, not Ruby. There are a number of situations where you need a goto in C that you wouldn't in Perl or Ruby because of the availability of named loop control.
    
    Secondly I don't see why you aren't using while to get the infinite loop rather than goto.
    
    Thirdly you can save some lines by not always using braces. For instance:
    
    if(rb_block_given_p()) rbBlock = rb_block_proc(); else
    - Re:I don't see the goto (Score:2)
      
      by djberg96 (2603)
      
      First of all that is written in C, not Ruby.
      I said is was a C extension for Ruby. I showed you the frontend. The C code above is the backend.
      Secondly I don't see why you aren't using while to get the infinite loop rather than goto.
      I suppose I could have done while(1) or something. It just didn't feel right.
      Thirdly you can save some lines by not always using braces.
      I hate that, sorry.
      - Re:I don't see the goto (Score:1)
        
        by btilly (5037)
        
        1, 3. Fair points.
        About the second. I'd suggest re-reading Go To Statement Considered Harmful [acm.org]. The fact that your indentation and control structures are in conflict makes your program's flow of control harder to understand upon first reading. Even if you aesthetically prefer a goto to an infinite while loop, I'd suggest that you indent from the label to the goto so that that section jumps out at the maintainer.
        
        Re:I don't see the goto (Score:2)
        
        by djberg96 (2603)
        
        I'd suggest that you indent from the label to the goto so that that section jumps out at the maintainer.
        Roger that. :)