Garbage collection and Arrays


#1

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:

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}” }

Is this a bug? Or is there something I’m missing? Thanks!

–Aaron


#2

On Fri, 12 Jan 2007, Aaron P. wrote:

ObjectSpace.each_object { |o| o_count[o.class] += 1 }

o_count.sort_by { |k,v| -v}.each { |k,v| puts “#{k}: #{v}” }

Is this a bug? Or is there something I’m missing? Thanks!

Check the archives of the list for extensive discussion. The upshot is
that it’s a problem with this shift() method.

Kirk H.


#3

On 1/12/07, Aaron P. removed_email_address@domain.invalid 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


#4

Aaron P. wrote:


Aaron P.
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: []


#5

On Fri, Jan 12, 2007 at 04:05:55PM +0900, Gregory B. wrote:

On 1/12/07, Aaron P. removed_email_address@domain.invalid 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!