sizeof(Class)/sizeof(Object)

ruby-talk
1

I would like to figure out how much memory a certain class or object
will/is consuming. Is there an easy way? Is there a hard way?
The reason I ask is because I want to keep several hundred thousand
instances of an object much like the following one:

class A
  def initialize
    @a = @b = @c = @d = nil
    @e = 1
  end
end

  nikolai

···

--
::: name: Nikolai Weibull :: aliases: pcp / lone-star / aka :::
::: born: Chicago, IL USA :: loc atm: Gothenburg, Sweden :::
::: page: www.pcppopper.org :: fun atm: gf,lps,ruby,lisp,war3 :::
main(){printf(&linux["\021%six\012\0"],(linux)["have"]+"fun"-97);}

2

Nikolai Weibull wrote:

I would like to figure out how much memory a certain class or object
will/is consuming. Is there an easy way? Is there a hard way?
The reason I ask is because I want to keep several hundred thousand
instances of an object much like the following one:

class A
  def initialize
    @a = @b = @c = @d = nil
    @e = 1
  end
end

Instance variables are stored in a hash table associated with each
object. See rb_ivar_set() in variable.c. So basically each instance
will take up the size of struct RObject - which is 20 bytes on a 32bit
machine, plus the size of the hash table (see st.h), plus something
else I am probably missing. As far as I know st.h doesn't provide any
means of calcing the number of bytes used by the hash.
Is there a way to do this?

Also, objects with no instance variables don't create a hash table to
store instance variables...

-Charlie

3

"Charles Mills" <cmills@freeshell.org> schrieb im Newsbeitrag news:1104515965.487836.265250@c13g2000cwb.googlegroups.com...

Nikolai Weibull wrote:

I would like to figure out how much memory a certain class or object
will/is consuming. Is there an easy way? Is there a hard way?
The reason I ask is because I want to keep several hundred thousand
instances of an object much like the following one:

class A
def initialize
@a = @b = @c = @d = nil
@e = 1
end

Instance variables are stored in a hash table associated with each
object. See rb_ivar_set() in variable.c. So basically each instance
will take up the size of struct RObject - which is 20 bytes on a 32bit
machine, plus the size of the hash table (see st.h), plus something
else I am probably missing. As far as I know st.h doesn't provide any
means of calcing the number of bytes used by the hash.
Is there a way to do this?

Also, objects with no instance variables don't create a hash table to
store instance variables...

So if there was only one instance var an optimization could be to store them in a hash in the instance's class. This could work for multiple ivars as well but then there is the array overhead. Hm...

class Foo
  @ivar = {}

  def initialize
    cl = self.class
    ObjectSpace.define_finalizer(self) {|id| cl.remove id}
  end

  def bar=(x) self.class.set_val(id, x) end
  def bar; self.class.get_val(id) end

  def self.set_val(id, val)
    @ivar[id] = val
  end

  def self.get_val(id)
    @ivar[id]
  end

  def self.remove(id)
    puts "removing #{id}"
    @ivar.delete id
  end
end

Just some thoughts in code...

    robert