From: Joel VanderWerf <vjoel@...>
Date: 2002-11-08T09:54:23+09:00
Subject: Re: bug in Fox or in Ruby -- round 2

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An update on the bug.

Problem 1:

Joel VanderWerf wrote:
 >
 > If I run this and press the "Pow!" button twice, I get a segfault. I've
 > tried whittling the example down, but everything seems to play a role...

Problem 2:

Maur�cio wrote:
  >   Hi,
  >
  >   An application I'm creating crashes ruby 1.73 (I'm using the windows
  > distribution from Pragmatic Programmers).
  >   The lines where the crash occurs (at least that's what the message
  > says) are:
  >
  > def float_translator (str)
  >   str.gsub(/([\d\+\-\.]+) (\+ | \-) (\d*) (\| | $)/ix){$1 + 'E' + $2 +
  > $3 + $4}.to_f
  > end


Now, I can recreate the former and maybe also the latter problem with a
fairly simple script. It uses FXRuby. Versions:

FXRuby-1.0.14
fox-1.0.26
ruby-1.7.3
linux-mandrake 8.1

Some observations:

* On my box, the segfault happens pretty reliably after 341 iterations.
The message is:

    ./bug2.rb:66: [BUG] rb_gc_mark() called for broken object
    ruby 1.7.3 (2002-09-27) [i686-linux]
    zsh: abort      ./bug2.rb

The line in question is a case statement involving regexes, which is
what suggests to me that this is related to Mauricio's bug.

My original app was much more complex, and the problem came up much
sooner. So there seems to be some connection with code complexity.


* GC.disable seems to prevent it from happening (well, I run out of swap
first, anyway). Looks like a ruby object isn't getting marked, or
malloced data is getting freed improperly.


* I tried to recreate the problem without FXRuby, but couldn't.


* I can't whittle the example down much farther in any dimension. For
example, the two lines

        old_nr = @table.numRows
        old_nc = @table.numCols

define local vars which are never used, but taking them out prevents the
bug (or delays it for more than 1000 iterations).

Another example, there is an unused branch of a case statement which
cannot be removed without losing the bug:

            case entry
            when /\A(.*\.)(.*)\z/
              entry = sprintf("%10.5f", entry.to_f).
                sub(/\.(\d*?)(0*)$/) { ".#{$1}#{$2.gsub("0", " ")}" }
            when /\d+/
              entry << " " * 6
            end

The first 'when' is never taken, but somehow parsing it is necessary to
expose the bug at iteration 341.


*** Can anyone shed any light on this murky situation? ***


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#!/usr/bin/env ruby

require "fox"
include Fox

if false
  puts "disabling GC"
  GC.disable  ### prevents bug
end

class BugWindow < FXMainWindow
  include Responder

  def initialize(app)
    super(app, "Bug2", nil, nil, DECOR_ALL, 0, 0, 0, 0)

    contents = FXHorizontalFrame.new(self,
      LAYOUT_SIDE_TOP|FRAME_NONE|LAYOUT_FILL_X|LAYOUT_FILL_Y)
    
    @table = FXTable.new(contents, 0, 0, nil, 0,
      TABLE_COL_SIZABLE|TABLE_ROW_SIZABLE|LAYOUT_FILL_X|LAYOUT_FILL_Y,
      0,0,0,0, 2,2,2,2)
  end
  
  def onPow(sender, sel, index)
    1000.times do |i|
      p i
      
      item = nil

      @table.setTableSize 0,0

      @header_row = ["foo"]*10
      @data_lines = []

      100.times { @data_lines << ["1"]*10 }

      old_nr = @table.numRows
      old_nc = @table.numCols

      # resize the table
      nr = @data_lines.size + 2
      nc = @header_row.size + 2
      @table.setTableSize(nr, nc)

      @table.leadingRows = 1
      @table.leadingCols = 1
      @table.trailingRows = 1
      @table.trailingCols = 1

      # The corners are just buttons
      @table.setItemText(0, 0, "")
      @table.getItem(0, 0).setButton(true)
      @table.setItemText(0, nc-1, "")
      @table.getItem(0, nc-1).setButton(true)
      @table.setItemText(nr-1, 0, "")
      @table.getItem(nr-1, 0).setButton(true)
      @table.setItemText(nr-1, nc-1, "")
      @table.setItemText(0, nc-1, "")

      # Initialize scrollable part of table
      entry = nil
      (1..nr-2).each { |r|
        (1..nc-2).each { |c|
          entry = @data_lines[r-1][c-1]
          case entry
          when /\A(.*\.)(.*)\z/
            entry = sprintf("%10.5f", entry.to_f).
              sub(/\.(\d*?)(0*)$/) { ".#{$1}#{$2.gsub("0", " ")}" }
          when /\d+/
            entry << " " * 6
          end
          @table.setItemText(r, c, entry)
        }
      }
    end

    return 1
  end
  
  def create
    position(200, 200, 600, 400)
    super
    show
  end
end

application = FXApp.new("TEST", "TEST")
application.init(ARGV)
window = BugWindow.new(application)
application.create
window.onPow(nil, nil, nil)


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