Redlander objects not garbage collected when references falls out of scope

[abargnesi]

Redlander objects (i.e. Redlander::Model, Redlander::Statement, etc) define a finalizer to free up the corresponding C pointers, however the finalizer never seems to be called. The following snippet shows this symptom:

require 'redlander'
include Redlander

Model.new
puts "count after Model new: #{ObjectSpace.each_object(Model).count}"
# => count after Model new: 1
GC.start
puts "run garbage collector; full mark and sweep"
# => run garbage collector; full mark and sweep
ObjectSpace.each_object(Model).count
puts "count after GC: #{ObjectSpace.each_object(Model).count}"
# => count after GC: 1

Here the Model.new reference is not retained so the allocated object should be freed, however we see the same number of allocations of the Model object.

[abargnesi]

I have taken a first pass on fixing the finalizers and spec test. I tried rspec should_receive assertions to verify the class method (self.finalize), but those tests failed. I tried something like

Uri.new('http://www.example.org')
Uri.should_receive(:finalize)
GC.start

[abargnesi]

Addressed issue double free'ing librdf_node pointers in Node and Statement finalizers.

[cordawyn]

Although the issue seem to have been addressed, we still need some sane testing for the memory alloc and release (see comments in #7). I'm leaving this issue open until we get those tests.

[abargnesi]

I will investigate using FFI for pointer cleanup tests. This would replace spec/integration/finalizer_gc_spec.rb which has proven unreliable.