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Re-use freed pages in BTree.FreeList
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lib/btree/free_list.ex
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lib/btree/free_list.ex
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@spec reserve_pages(t, non_neg_integer) :: [non_neg_integer]
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def reserve_pages(free_list, count) do
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{freed_indexes, reserved_count} = do_reserve_free_pages(free_list, count, [], 0)
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case reserved_count == count do
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true ->
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freed_indexes
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false ->
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assert reserved_count < count
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allocated_indexes = allocate_new_pages(free_list, count - reserved_count)
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Enum.reverse(freed_indexes, allocated_indexes)
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end
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[{:max_index, max_index}] = :ets.lookup(free_list, :max_index)
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:ets.insert(free_list, {:max_index, max_index + count})
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Enum.to_list((max_index + 1)..(max_index + count))
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end
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defp allocate_new_pages(free_list, count) do
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[{:max_index, old_max_index}] = :ets.lookup(free_list, :max_index)
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new_max_index = old_max_index + count
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:ets.insert(free_list, {:max_index, new_max_index})
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Enum.to_list(old_max_index..(new_max_index - 1))
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end
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defp do_reserve_free_pages(_free_list, target_count, acc, count_acc)
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when count_acc == target_count do
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{acc, count_acc}
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end
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defp do_reserve_free_pages(free_list, target_count, acc, count_acc) do
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case :ets.next(free_list, [:free | -1]) do
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[:free | index] = key ->
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:ets.delete(free_list, key)
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acc = [index | acc]
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count_acc = count_acc + 1
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do_reserve_free_pages(free_list, target_count, acc, count_acc)
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_ ->
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{acc, count_acc}
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end
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end
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@spec free_page(t, non_neg_integer) :: :ok