What's the point: FREE in ObjectSpace.count_objects on ruby MRI
I would like to know what the count associated with the key :FREE
was returning from ObjectSpace.count_object
. The documentation says that this hash is implementation specific, so my question is specific to the MRI 2.1 ruby.
There have been at least two questions here ( here and here ) but no answers regarding :FREE
.
Any ideas?
In some cases, the free account far exceeds the number of properties available through ObjectSpace.each_object
, and hence I don't seem to have any information about them. They take up memory. In my program, the count :FREE
is high even after starting garbage collection.
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We can find the value :FREE
directly from the implementation itself (from gc.c )
* The keys starting with +:T_+ means live objects.
* For example, +:T_ARRAY+ is the number of arrays.
* +:FREE+ means object slots which is not used now.
* +:TOTAL+ means sum of above.
Then we can take a look at the tests for it (from test_gc.rb ):
assert_equal(count[:TOTAL]-count[:FREE], stat[:heap_live_slots])
assert_equal(count[:FREE], stat[:heap_free_slots])
And finally, we can check if there is a funny case:
GC.stat[:heap_free_slot] == ObjectSpace.count_objects[:FREE]
irb(main):001:0> GC.stat[:heap_free_slot] == ObjectSpace.count_objects[:FREE]
=> true
So, :FREE
indicates the number of allocated slots in the heap that have not been used.
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