From: bbiker <renard@...>
Date: 2007-01-14T15:25:06+09:00
Subject: Re: Garbage collection and Arrays


Aaron Patterson wrote:
> On Fri, Jan 12, 2007 at 04:05:55PM +0900, Gregory Brown wrote:
> > On 1/12/07, Aaron Patterson <aaron_patterson@speakeasy.net> wrote:
> > >Hi, I seem to be running in to some garbage collection weirdness.
> > >Hopefully someone will have some insight for me....  My sample script
> > >seems to leak Strings when I use shift on an Array, but not pop:
> >
> > http://recursive.ca/hutch/index.php?p=361
> >
>
> Thanks!
>
> --
> Aaron Patterson
> http://tenderlovemaking.com/

The workaround to eliminate leakage with array.shift works except that
shift no longer returns the shifted element and instead returns nil

The following class allows shift to work normally without the leakage
... I know it is only a temporary work around until the ruby developers
get around to fix the c code

####  Array#shift ###############
class Array
  alias :orig_shift :shift
  def shift
    return nil if self.empty?
    ret = self[0]
    self[0] = nil
    self.orig_shift
    return ret
  end
end

###### code to show that the leakage has been eliminated
separator = "---"
o_count = Hash.new(0)
GC.start

ObjectSpace.each_object { |o| o_count[o.class] += 1 }
o_count.sort_by { |k,v| -v}.each { |k,v| puts "#{k}: #{v}" }
o_count = nil
puts separator

array = []
10.times { array << "foo" }
10.times { array.pop }  # Change this to shift to see a leak

o_count = Hash.new(0)
GC.start
ObjectSpace.each_object { |o| o_count[o.class] += 1 }
o_count.sort_by { |k,v| -v}.each { |k,v| puts "#{k}: #{v}" }
array = nil
o_count = nil

puts separator
array = []
10.times { array << "foo" }
10.times { array.shift }  # Change this to shift to see a leak

o_count = Hash.new(0)
GC.start
ObjectSpace.each_object { |o| o_count[o.class] += 1 }
o_count.sort_by { |k,v| -v}.each { |k,v| puts "#{k}: #{v}" }

__END__

#######  test results   only pertinent data shown
NEW shift method

        before pop      after pop
                        before shift       after shift
String: 1746            1764               1764
Array:  70                71                  72

OLD shift methed   --  Class Array commented out
        before pop      after pop
                        before shift       after shift
String: 1746            1764               1774
Array:  70                71                  72


##################  code to show that Array#shift behaves as described
in the ri documentation

class Array
  alias :orig_shift :shift
  def shift
    return nil if self.empty?
    ret = self[0]
    self[0] = nil
    self.orig_shift
    return ret
  end
end

a = (1..5).to_a

1.upto(10) do |i|
  x = a.shift

  puts "#{i}: \tx: #{x.inspect} \ta: #{a.inspect}"
end

__END__


1: 	x: 1 	a: [2, 3, 4, 5]
2: 	x: 2 	a: [3, 4, 5]
3: 	x: 3 	a: [4, 5]
4: 	x: 4 	a: [5]
5: 	x: 5 	a: []
6: 	x: nil 	a: []
7: 	x: nil 	a: []
8: 	x: nil 	a: []
9: 	x: nil 	a: []
10: x: nil 	a: []