Class: PEROBS::BigArrayNode

Inherits:
Object show all
Defined in:
lib/perobs/BigArrayNode.rb

Overview

The BigArrayNode class provides the BTree nodes for the BigArray objects. A node can either be a branch node or a leaf node. Branch nodes don’t store values, only offsets and references to child nodes. Leaf nodes don’t have child nodes but store the actual values. The leaf nodes always contain at least node_size / 2 number of consecutive values. The index of the first value in the BigArray is the sum of the offsets stored in the parent nodes. Branch nodes store the offsets and the corresponding child node references. The first offset is always 0. Consecutive offsets are set to the previous offset plus the total number of values stored in the previous child node. The leaf nodes don’t contain wholes. A concatenation of all leaf node values represents the stored Array.

Root Node -------------------------------- Offsets | 0 11 | Children | |

v                            v

Level 1 --------------------------+————————–+ Offsets | 0 4 7 || 0 2 5 | Children | | | | | |

v         v         v         v          v         v

Leaves ---------+——-----------——-----------——-+ Values | A B C D || E F G || H I J K || L M || N O P || Q R |

Index 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Constant Summary

Constants inherited from ObjectBase

ObjectBase::NATIVE_CLASSES

Instance Attribute Summary

Attributes inherited from Object

#attributes

Attributes inherited from ObjectBase

#_id, #myself, #store

Instance Method Summary collapse

Methods inherited from Object

#_delete_reference_to_id, #_deserialize, #_referenced_object_ids, #attr_init, attr_persist, #init_attr, #inspect, #mark_as_modified

Methods inherited from ObjectBase

#==, #_check_assignment_value, _finalize, #_initialize, #_restore, #_stash, #_sync, #_transfer, read, #restore

Constructor Details

#initialize(p, tree, is_leaf, parent = nil, prev_sibling = nil, next_sibling = nil) ⇒ BigArrayNode

Internal constructor. Use Store.new(BigArrayNode, …) instead.

Parameters:

  • p (Handle)
  • tree (BigArray) —

    The tree this node should belong to

  • is_leaf (Boolean) —

    True if a leaf node should be created, false for a branch node.

  • parent (BigArrayNode) (defaults to: nil) —

    Parent node

  • prev_sibling (BigArrayNode) (defaults to: nil) —

    Previous sibling

  • next_sibling (BigArrayNode) (defaults to: nil) —

    Next sibling



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# File 'lib/perobs/BigArrayNode.rb', line 70

def initialize(p, tree, is_leaf, parent = nil,
               prev_sibling = nil, next_sibling = nil)
  super(p)
  self.tree = tree
  self.parent = parent

  if is_leaf
    # Create a new leaf node. It stores values and has no children.
    self.values = @store.new(PEROBS::Array)
    self.children = self.offsets = nil

    # Link the neighboring siblings to the newly inserted node.  If the
    # node has no sibling on a side we also must register it as first or
    # last leaf with the BigArray object.
    if (self.prev_sibling = prev_sibling)
      @prev_sibling.next_sibling = myself
    else
      @tree.first_leaf = myself
    end
    if (self.next_sibling = next_sibling)
      @next_sibling.prev_sibling = myself
    else
      @tree.last_leaf = myself
    end
  else
    # Create a new branch node. It stores keys and child node references
    # but no values.
    self.offsets = @store.new(PEROBS::Array)
    self.children = @store.new(PEROBS::Array)
    self.values = nil
    # Branch nodes don't need sibling links.
    self.prev_sibling = self.next_sibling = nil
  end
end

Instance Method Details

#adjust_offsets(after_child, delta) ⇒ Object

This method takes care of adjusting the offsets in tree in case elements were inserted or removed. All nodes that hold children after the insert/remove operation need to be adjusted. Since child nodes get their offsets via their parents, only the parent node and the direct ancestor followers need to be adjusted.

Parameters:

  • after_child (BigArrayNode) —

    specifies the modified leaf node

  • delta (Integer) —

    specifies how many elements were inserted or removed.



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# File 'lib/perobs/BigArrayNode.rb', line 659

def adjust_offsets(after_child, delta)
  node = self

  while node
    adjust = false
    0.upto(node.children.size - 1) do |i|
      # Iterate over the children until we have found the after_child
      # node. Then turn on adjustment mode. The offsets of the following
      # entries will be adjusted by delta.
      if adjust
        node.offsets[i] += delta
      elsif node.children[i] == after_child
        adjust = true
      end
    end

    unless adjust
      node.fatal "Could not find child #{after_child._id}"
    end

    after_child = node
    node = node.parent
  end
end

#check {|key, value| ... } ⇒ Boolean

Check consistency of the node and all subsequent nodes. In case an error is found, a message is logged and false is returned.

Yields:

  • (key, value)

Returns:

  • (Boolean) —

    true if tree has no errors



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# File 'lib/perobs/BigArrayNode.rb', line 277

def check
  branch_depth = nil

  traverse do |node, position, stack|
    if position.zero?
      # Nodes should have between min_size() and
      # @tree.node_size children or values. Only the root node may have
      # less.
      if node.size > @tree.node_size
        node.error "BigArray node #{node._id} is too large. It has " \
                   "#{node.size} nodes instead of max. #{@tree.node_size}."
        return false
      end
      if node.parent && node.size < min_size
        node.error "BigArray node #{node._id} is too small"
        return false
      end

      if node.is_leaf?
        # All leaf nodes must have same distance from root node.
        if branch_depth
          unless branch_depth == stack.size
            node.error 'All leaf nodes must have same distance from root'
            return false
          end
        else
          branch_depth = stack.size
        end

        return false unless node.check_leaf_node_links

        if node.children
          node.error 'children must be nil for a leaf node'
          return false
        end
      else
        unless node.children.size == node.offsets.size
          node.error "Offset count (#{node.offsets.size}) must be equal " \
                     "to children count (#{node.children.size})"
          return false
        end

        if node.values
          node.error 'values must be nil for a branch node'
          return false
        end

        unless @prev_sibling.nil? && @next_sibling.nil?
          node.error 'prev_sibling and next_sibling must be nil for ' \
                     'branch nodes'
        end

        return false unless node.check_offsets

        return false unless node.check_child_nodes(stack)
      end
    elsif position <= node.size
      # These checks are done after we have completed the respective child
      # node with index 'position - 1'.
      index = position - 1
      if node.is_leaf? && block_given?
        # If a block was given, call this block with the key and value.
        return false unless yield(node.first_index + index,
                                  node.values[index])
      end
    end
  end

  true
end

#check_child_nodes(stack) ⇒ Object 



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# File 'lib/perobs/BigArrayNode.rb', line 406

def check_child_nodes(stack)
  if @children.uniq.size != @children.size
    error "Node #{@_id} has multiple identical children"
    return false
  end

  @children.each_with_index do |child, i|
    unless child.is_a?(BigArrayNode)
      error "Child #{@_id} is of class #{child.class} " \
            'instead of BigArrayNode'
      return false
    end

    unless child.parent.is_a?(BigArrayNode)
      error "Parent reference of child #{i} is of class " \
            "#{child.class} instead of BigArrayNode"
      return false
    end

    if child.parent != self
      error "Child node #{child._id} has wrong parent " \
            "#{child.parent._id}. It should be #{@_id}."
      return false
    end

    if child == self
      error "Child #{i} point to self"
      return false
    end

    if stack.include?(child)
      error "Child #{i} points to ancester node"
      return false
    end

    unless child.parent == self
      error "Child #{i} does not have parent pointing " \
            'to this node'
      return false
    end
  end

  true
end

#check_leaf_node_links ⇒ Object 



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# File 'lib/perobs/BigArrayNode.rb', line 348

def check_leaf_node_links
  if @prev_sibling.nil?
    if @tree.first_leaf != self
      error "Leaf node #{@_id} has no previous sibling " \
            'but is not the first leaf of the tree'
      return false
    end
  elsif @prev_sibling.next_sibling != self
    error 'next_sibling of previous sibling does not point to ' \
          'this node'
    return false
  end

  if @next_sibling.nil?
    if @tree.last_leaf != self
      error "Leaf node #{@_id} has no next sibling " \
            'but is not the last leaf of the tree'
      return false
    end
  elsif @next_sibling.prev_sibling != self
    error 'previous_sibling of next sibling does not point to ' \
          'this node'
    return false
  end

  true
end

#check_offsets ⇒ Object 



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# File 'lib/perobs/BigArrayNode.rb', line 376

def check_offsets
  return true if @parent.nil? && @offsets.empty?

  if @offsets[0] != 0
    error "First offset is not 0: #{@offsets.inspect}"
    return false
  end

  last_offset = nil
  @offsets.each_with_index do |offset, i|
    if i.positive?
      if offset < last_offset
        error 'Offsets are not strictly monotoneously ' \
              "increasing: #{@offsets.inspect}"
        return false
      end
      expected_offset = last_offset + @children[i - 1].values_count
      if offset != expected_offset
        error "Offset #{i} must be #{expected_offset} " \
              "but is #{offset}."
        return false
      end
    end

    last_offset = offset
  end

  true
end

#consolidate_child_nodes(child) ⇒ Object 



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# File 'lib/perobs/BigArrayNode.rb', line 576

def consolidate_child_nodes(child)
  unless (child_index = @children.index(child))
    error "Cannot find child to consolidate"
  end

  if child_index == 0
    # Consolidate with successor if it exists.
    return unless (succ = @children[child_index + 1])

    if child.size + succ.size <= @tree.node_size
      # merge child with successor
      merge_child_with_next(child_index)
    else
      move_first_element_of_successor_to_child(child_index)
    end
  else
    # consolidate with predecessor
    pred = @children[child_index - 1]

    if pred.size + child.size <= @tree.node_size
      # merge child with predecessor
      merge_child_with_next(child_index - 1)
    else
      move_last_element_of_predecessor_to_child(child_index)
    end
  end
end

#delete_at(index) ⇒ Object

Delete the element at the specified index, returning that element, or nil if the index is out of range.

Parameters:

  • index (Integer) —

    Index in the BigArray

Returns:

  • (Object) —

    found value or nil



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# File 'lib/perobs/BigArrayNode.rb', line 225

def delete_at(index)
  node = self
  deleted_value = nil

  while node
    if node.is_leaf?
      deleted_value = node.values.delete_at(index)
      if node.parent
        node.parent.adjust_offsets(node, -1)
        node.parent.consolidate_child_nodes(node) if node.size < min_size
      end

      return deleted_value
    else
      # Descend into the right child node to add the value to.
      cidx = (node.offsets.bsearch_index { |o| o > index } ||
              node.offsets.length) - 1
      if (index -= node.offsets[cidx]).negative?
        node.fatal "Index (#{index}) became negative"
      end
      node = node.children[cidx]
    end
  end

  PEROBS.log.fatal 'Could not find proper node to delete from while ' \
                   "looking for index #{index}"
end

#each {|value| ... } ⇒ Object

Iterate over all the values of the node.

Yields:

  • (value) 


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# File 'lib/perobs/BigArrayNode.rb', line 255

def each
  return nil unless is_leaf?

  @values.each do |v|
    yield(v)
  end
end

#error(msg) ⇒ Object

Print and log an error message for the node.



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# File 'lib/perobs/BigArrayNode.rb', line 797

def error(msg)
  msg = "Error in BigArray node @#{@_id}: #{msg}\n" + @tree.to_s
  $stderr.puts msg
  PEROBS.log.error msg
end

#fatal(msg) ⇒ Object

Print and log an error message for the node.



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# File 'lib/perobs/BigArrayNode.rb', line 804

def fatal(msg)
  msg = "Fatal error in BigArray node @#{@_id}: #{msg}\n"
  $stderr.puts msg
  PEROBS.log.fatal msg
end

#first_index ⇒ Object 



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# File 'lib/perobs/BigArrayNode.rb', line 621

def first_index
  # TODO: This is a very expensive method. Find a way to make this way
  # faster.
  node = parent
  child = myself
  while node
    if (index = node.children.index(child)) && index > 0
      return node.offsets[index - 1]
    end
    child = node
    node = node.parent
  end

  0
end

#get(index) ⇒ Integer or nil

Return the value that matches the given key or return nil if they key is unknown.

Parameters:

  • index (Integer) —

    Position to insert at

Returns:

  • (Integer or nil) —

    value that matches the key



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# File 'lib/perobs/BigArrayNode.rb', line 200

def get(index)
  node = self

  # Traverse the tree to find the right node to add or replace the value.
  while node
    # Once we have reached a leaf node we can insert or replace the value.
    return node.values[index] if node.is_leaf?

    # Descend into the right child node to add the value to.
    cidx = (node.offsets.bsearch_index { |o| o > index } ||
            node.offsets.length) - 1
    if (index -= node.offsets[cidx]).negative?
      node.fatal "Index (#{index}) became negative"
    end
    node = node.children[cidx]
  end

  PEROBS.log.fatal 'Could not find proper node to get from while ' \
                   "looking for index #{index}"
end

#index_in_parent_node ⇒ Object

node. If the node is the root node, nil is returned.

Returns:

  • The index of the current node in the children list of the parent



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# File 'lib/perobs/BigArrayNode.rb', line 615

def index_in_parent_node
 return nil unless @parent

 @parent.children.find_index(self)
end

#insert(index, value) ⇒ Object

Insert the given value at the given index. All following values will be pushed to a higher index.

Parameters:

  • index (Integer) —

    Position to insert at

  • value (Integer) —

    value to insert



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# File 'lib/perobs/BigArrayNode.rb', line 162

def insert(index, value)
  node = self
  cidx = nil

  # Traverse the tree to find the right node to add or replace the value.
  while node
    # All nodes that we find on the way that are full will be split into
    # two half-full nodes.
    if node.size >= @tree.node_size
      # Re-add the index from the last parent node since we will descent
      # into one of the split nodes.
      index += node.parent.offsets[cidx] if node.parent
      node = node.split_node
    end

    # Once we have reached a leaf node we can insert or replace the value.
    if node.is_leaf?
      node.values.insert(index, value)
      node.parent&.adjust_offsets(node, 1)
      return
    else
      # Descend into the right child node to add the value to.
      cidx = node.search_child_index(index)
      if (index -= node.offsets[cidx]).negative?
        node.fatal "Index (#{index}) became negative"
      end
      node = node.children[cidx]
    end
  end

  node.fatal 'Could not find proper node to insert the value while ' \
             "looking for index #{index}"
end

#insert_child_after_peer(offset, node, peer = nil) ⇒ Object 



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# File 'lib/perobs/BigArrayNode.rb', line 569

def insert_child_after_peer(offset, node, peer = nil)
  peer_index = @children.find_index(peer)
  cidx = peer_index ? peer_index + 1 : 0
  @offsets.insert(cidx, @offsets[peer_index] + offset)
  @children.insert(cidx, node)
end

#is_leaf? ⇒ Boolean

Returns True if this is a leaf node, false otherwise.

Returns:

  • (Boolean) —

    True if this is a leaf node, false otherwise.



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# File 'lib/perobs/BigArrayNode.rb', line 106

def is_leaf?
  @children.nil?
end

#reverse_each {|value| ... } ⇒ Object

Iterate over all the values of the node in reverse order.

Yields:

  • (value) 


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# File 'lib/perobs/BigArrayNode.rb', line 265

def reverse_each
  return nil unless is_leaf?

  @values.reverse_each do |v|
    yield(v)
  end
end

#search_child_index(offset) ⇒ Integer

Returns Index of the matching offset or the insert position.

Parameters:

  • offset (Integer) —

    offset to search the child index for

Returns:

  • (Integer) —

    Index of the matching offset or the insert position.



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# File 'lib/perobs/BigArrayNode.rb', line 606

def search_child_index(offset)
  # Handle special case for empty offsets list.
  return 0 if @offsets.empty? || offset <= @offsets.first

  (@offsets.bsearch_index { |o| o > offset } || @offsets.length) - 1
end

#set(index, value) ⇒ Object

Set the given value at the given index.

Parameters:

  • index (Integer) —

    Position to insert at

  • value (Integer) —

    value to insert



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# File 'lib/perobs/BigArrayNode.rb', line 129

def set(index, value)
  node = self

  # Traverse the tree to find the right node to add or replace the value.
  idx = index
  while node
    # Once we have reached a leaf node we can insert or replace the value.
    if node.is_leaf?
      if idx >= node.values.size
        node.fatal "Set index (#{index}) larger than values array " \
                   "(#{idx} >= #{node.values.size})."
      end
      node.values[idx] = value
      return
    else
      # Descend into the right child node to add the value to.
      cidx = node.search_child_index(idx)
      if (idx -= node.offsets[cidx]).negative?
        node.fatal "Idx (#{idx}) became negative while looking for " \
                   "index #{index}."
      end
      node = node.children[cidx]
    end
  end

  node.fatal 'Could not find proper node to set the value while ' \
             "looking for index #{index}."
end

#size ⇒ Object 



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# File 'lib/perobs/BigArrayNode.rb', line 110

def size
  is_leaf? ? @values.size : @children.size
end

#split_node ⇒ BigArrayNode

Split the current node into two nodes. The upper half of the elements will be moved into a newly created node. This node will retain the lower half.

Returns:



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# File 'lib/perobs/BigArrayNode.rb', line 488

def split_node
  unless @parent
    # The node is the root node. We need to create a parent node first.
    self.parent = @store.new(BigArrayNode, @tree, false)
    @parent.offsets[0] = 0
    @parent.children[0] = myself
    @tree.root = @parent
  end

  # Create the new sibling that will take the 2nd half of the
  # node content.
  sibling = @store.new(BigArrayNode, @tree, is_leaf?, @parent, myself,
                       @next_sibling)
  # Determine the index of the middle element that gets moved to the
  # parent. The node size must be an uneven number.
  mid = size / 2
  if is_leaf?
    # Before:
    #    +--------------------------+
    #    | 0         4         7    |
    #      |         |         |
    #      v         v         v
    # +---------++-------++----------+
    # | A B C D || E F G || H I J K  |
    #
    # After:
    #    +--------------------------+
    #    | 0    2       4         7 |
    #      |    |       |         |
    #      v    v       v         v
    # +-----++----++-------++----------+
    # | A B || C D || E F G || H I J K  |
    #
    #
    # Insert the middle element key into the parent node
    @parent.insert_child_after_peer(mid, sibling, self)
    # Copy the values from the mid element onwards into the new
    # sibling node.
    sibling.values += @values[mid..-1]
    # Delete the copied offsets and values from this node.
    @values.slice!(mid..-1)
  else
    # Before:
    #    +--------------+
    #    | 0         11 |
    #      |          |
    #      v          v
    # +----------++-------+
    # | 0 4 7 10 || 0 2 5 |
    #   | | | |     | | |
    #   v v v v     v v v
    #
    # After:
    #  +------------------+
    #  | 0      7      11 |
    #    |      |       |
    #    v      v       v
    # +-----++-----++-------+
    # | 0 4    0 3 || 0 2 5 |
    #   | |    | |    | | |
    #   v v    v v    v v v
    #
    # Insert the new sibling into the parent node.
    offset_delta = @offsets[mid]
    @parent.insert_child_after_peer(offset_delta, sibling, self)
    # Copy the offsets from after the mid value onwards to the new sibling
    # node. We substract the offset delta from each of them.
    sibling.offsets += @offsets[mid..-1].map{ |v| v - offset_delta }
    # Delete the copied offsets from this node.
    @offsets.slice!(mid..-1)
    # Same copy for the children.
    sibling.children += @children[mid..-1]
    # Reparent the children to the new sibling parent.
    sibling.children.each { |c| c.parent = sibling }
    # And delete the copied children references.
    @children.slice!(mid..-1)
  end

  @parent
end

#statistics(stats) ⇒ Object

Gather some statistics about the node and all sub nodes.

Parameters:

  • stats (Stats) —

    Data structure that stores the gathered data



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# File 'lib/perobs/BigArrayNode.rb', line 721

def statistics(stats)
  traverse do |node, position, stack|
    if position == 0
      if node.is_leaf?
        stats.leaf_nodes += 1
        depth = stack.size + 1
        if stats.min_depth.nil? || stats.min_depth < depth
          stats.min_depth = depth
        end
        if stats.max_depth.nil? || stats.max_depth > depth
          stats.max_depth = depth
        end
      else
        stats.branch_nodes += 1
      end
    end
  end
end

#to_s ⇒ String

Returns Human reable form of the sub-tree.

Returns:

  • (String) —

    Human reable form of the sub-tree.



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# File 'lib/perobs/BigArrayNode.rb', line 452

def to_s
  str = ''

  traverse do |node, position, stack|
    if position.zero?
      begin
        str += "#{node.parent ? node.parent.tree_prefix + '  +' : 'o'}" \
               "#{node.tree_branch_mark}-" \
               "#{node.empty? ? '--' : 'v-'}#{node.tree_summary}\n"
      rescue => e
        str += "@@@@@@@@@@: #{e.message}\n"
      end
    else
      begin
        if node.is_leaf?
          if position <= node.size
            str += "#{node.tree_prefix}  " \
                   "#{position == node.size ? '-' : '|'} " \
                   "[ #{node.value_index(position - 1)}: " \
                   "#{node.values[position - 1].nil? ?
                   'nil' : node.values[position - 1]} ]\n"
          end
        end
      rescue => e
        str += "@@@@@@@@@@: #{e.message}\n"
      end
    end
  end

  str
end

#traverse {|node, position, stack| ... } ⇒ Object

This is a generic tree iterator. It yields before it descends into the child node and after (which is identical to before the next child descend). It yields the node, the position and the stack of parent nodes.

Yields:

  • (node, position, stack) 


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# File 'lib/perobs/BigArrayNode.rb', line 689

def traverse
  # We use a non-recursive implementation to traverse the tree. This stack
  # keeps track of all the known still to be checked nodes.
  stack = [ [ self, 0 ] ]

  while !stack.empty?
    node, position = stack.pop

    # Call the payload method. The position marks where we are in the node
    # with respect to the traversal. 0 means we've just entered the node
    # for the first time and are about to descent to the first child.
    # Position 1 is after the 1st child has been processed and before the
    # 2nd child is being processed. If we have N children, the last
    # position is N after we have processed the last child and are about
    # to return to the parent node.
    yield(node, position, stack)

    if position <= node.size
      # Push the next position for this node onto the stack.
      stack.push([ node, position + 1 ])

      if !node.is_leaf? && node.children[position]
        # If we have a child node for this position, push the linked node
        # and the starting position onto the stack.
        stack.push([ node.children[position], 0 ])
      end
    end
  end
end

#tree_branch_mark ⇒ Object

Branch node decoration for the inspection method.



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# File 'lib/perobs/BigArrayNode.rb', line 763

def tree_branch_mark
  return '' unless @parent
  '-'
end

#tree_prefix ⇒ Object

Return the decoration that marks the tree structure of this node for the inspection method.



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# File 'lib/perobs/BigArrayNode.rb', line 742

def tree_prefix
  node = self
  str = ''

  while node
    is_last_child = false
    if node.parent
      is_last_child = node.parent.children.last == node
    else
      # Don't add lines for the top-level.
      break
    end

    str = (is_last_child ? '   ' : '  |') + str
    node = node.parent
  end

  str
end

#tree_summary ⇒ Object

Text for the node line for the inspection method.



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# File 'lib/perobs/BigArrayNode.rb', line 769

def tree_summary
  s = " @#{@_id}"
  if @parent
    begin
      s += " +#{@parent.offsets[index_in_parent_node]} ^#{@parent._id}"
    rescue
      s += ' ^@'
    end
  end
  if @prev_sibling
    begin
      s += " <#{@prev_sibling._id}"
    rescue
      s += ' <@'
    end
  end
  if @next_sibling
    begin
      s += " >#{@next_sibling._id}"
    rescue
      s += ' >@'
    end
  end

  s
end

#value_index(idx) ⇒ Integer

Compute the array index of the value with the given index in the current node.

Parameters:

  • idx (Integer) —

    Index of the value in the current node

Returns:

  • (Integer) —

    Array index of the value



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# File 'lib/perobs/BigArrayNode.rb', line 641

def value_index(idx)
  node = self
  while node.parent
    idx += node.parent.offsets[node.index_in_parent_node]
    node = node.parent
  end

  idx
end

#values_count ⇒ Integer

Returns the number of values stored in this node.

Returns:

  • (Integer) —

    the number of values stored in this node.



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# File 'lib/perobs/BigArrayNode.rb', line 115

def values_count
  count = 0
  node = self
  while node
    return count + node.values.size if node.is_leaf?

    count += node.offsets.last
    node = node.children.last
  end
end