tables and the gc

["Tom Spilman" <tom@...>]

I have the following code (i'm using luabind, but this is a lua 
issue )...


  class 'my_class1'

  function my_class1:__init()

    self._my_hardware_resource = create_hardware_resource()

  end


  class 'my_class2'

  function my_class2:__init()

    self._my_class1 = my_class1()

  end

  function my_class2:free_hardware_resources()

    self._my_class1 = nil

    -- note that the class above is still not
    -- released... must gc.
    collectgarbage()

    -- now 'my_class1' has been gc'ed, but
    -- the internal member '_my_hardware_resource'
    -- has not... must call gc again to do that.
    collectgarbage()

  end


  Looking at my_class2.free_hardware_resources() you can see what my 
problem is.  It seems that the first garbage collection pass will 
free a table ( the class members are in a table ), but will not free 
newly unreferenced members of that table.  A second garbage 
collection pass is needed to do that.  I assume that if i had a 
deeper hierarchy i'd need to call the garbage collection call once 
per level to ensure resources i have to have freed are.

  Ok... stop the madness... what is the right way for me to free 
something that must be destroyed immediately?  I'm thinking 
a "destructor" for 'my_class1' would be once solution as i could nil 
the member before the gc call.  Still calling collectgarbage() to 
force the destruction of one object seems like overkill to me.  
Should i just be using a different design pattern than what i've 
used in other languages for years?

  Tom