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Under the hood memory management, w/o Garbage collection.

liorscotland

Hello all. Let us say that I have this (simplistic) code:
a=list( 1 2 3 4 5 6 7 8 )
a=car(a)
b=list(2 3 4)
The question is this: assuming that no "proper" garbage collection has been done. I.e., if the next command after b=list(1 2 3) will be gc(), memory footprint will change.
What happens is that a now takes far less space than it did in the past. Now b consumes more memory.
What will the SKILL engine do?

1. allocate more memory to contain variable b, and subsequent memory requiring
2. It will it use the memory release, after variable a needs less space, and garbage collection will simply relieve any excess memory?
My guess would be that  item 1 will happen.

Thanks.

Parents

  • Hi Lior,

    I'm not sure I entirely understand your question (or maybe the reason for the question). In general for each type, there is a "heap" of unused space which gets consumed as needed - so as new list cells are needed, it will eat into that unused space for list cells. When it runs out of these unused list cells, it will do a garbage collection to see if it can reclaim unreachable list cells and avoid having to allocate more memory. If there are none that can be reclaimed, it will allocate another chunk of list cells into the heap and start consuming those.

    In your example, the original list becomes unreachable and also all 8 list cells (assuming nothing else is referring to them) become "garbage". They might get re-used when b is created, but that depends on the available list cells in the heap (in practice the gc heuristics are a bit more complicated than I've described, but it's the general principle).

    Regards,

    Andrew.

Reply

  • Hi Lior,

    I'm not sure I entirely understand your question (or maybe the reason for the question). In general for each type, there is a "heap" of unused space which gets consumed as needed - so as new list cells are needed, it will eat into that unused space for list cells. When it runs out of these unused list cells, it will do a garbage collection to see if it can reclaim unreachable list cells and avoid having to allocate more memory. If there are none that can be reclaimed, it will allocate another chunk of list cells into the heap and start consuming those.

    In your example, the original list becomes unreachable and also all 8 list cells (assuming nothing else is referring to them) become "garbage". They might get re-used when b is created, but that depends on the available list cells in the heap (in practice the gc heuristics are a bit more complicated than I've described, but it's the general principle).

    Regards,

    Andrew.

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