class Puppet::SimpleGraph

A hopefully-faster graph class to replace the use of GRATR.

Attributes

use_new_yaml_format[RW]

Public Class Methods

new() click to toggle source

All public methods of this class must maintain (assume ^ ensure) the following invariants, where “=~=” means equiv. up to order:

@in_to.keys =~= @out_to.keys =~= all vertices
@in_to.values.collect { |x| x.values }.flatten =~= @out_from.values.collect { |x| x.values }.flatten =~= all edges
@in_to[v1][v2] =~= @out_from[v2][v1] =~= all edges from v1 to v2
@in_to   [v].keys =~= vertices with edges leading to   v
@out_from[v].keys =~= vertices with edges leading from v
no operation may shed reference loops (for gc)
recursive operation must scale with the depth of the spanning trees, or better (e.g. no recursion over the set
    of all vertices, etc.)

This class is intended to be used with DAGs. However, if the graph has a cycle, it will not cause non-termination of any of the algorithms.

# File lib/puppet/simple_graph.rb, line 24
def initialize
  @in_to = {}
  @out_from = {}
  @upstream_from = {}
  @downstream_from = {}
end

Public Instance Methods

add_edge(e,*a) click to toggle source

Add a new edge. The graph user has to create the edge instance, since they have to specify what kind of edge it is.

# File lib/puppet/simple_graph.rb, line 291
def add_edge(e,*a)
  return add_relationship(e,*a) unless a.empty?
  @upstream_from.clear
  @downstream_from.clear
  add_vertex(e.source)
  add_vertex(e.target)
  @in_to[   e.target][e.source] ||= []; @in_to[   e.target][e.source] |= [e]
  @out_from[e.source][e.target] ||= []; @out_from[e.source][e.target] |= [e]
end

add_relationship(source, target, label = nil) click to toggle source

# File lib/puppet/simple_graph.rb, line 301
def add_relationship(source, target, label = nil)
  add_edge Puppet::Relationship.new(source, target, label)
end

add_vertex(vertex) click to toggle source

Add a new vertex to the graph.

# File lib/puppet/simple_graph.rb, line 264
def add_vertex(vertex)
  @in_to[vertex]    ||= {}
  @out_from[vertex] ||= {}
end

adjacent(v, options = {}) click to toggle source

Find adjacent edges.

# File lib/puppet/simple_graph.rb, line 334
def adjacent(v, options = {})
  return [] unless ns = (options[:direction] == :in) ? @in_to[v] : @out_from[v]
  (options[:type] == :edges) ? ns.values.flatten : ns.keys
end

clear() click to toggle source

Clear our graph.

# File lib/puppet/simple_graph.rb, line 32
def clear
  @in_to.clear
  @out_from.clear
  @upstream_from.clear
  @downstream_from.clear
end

dependencies(resource) click to toggle source

Which resources depend upon the given resource.

# File lib/puppet/simple_graph.rb, line 40
def dependencies(resource)
  vertex?(resource) ? upstream_from_vertex(resource).keys : []
end

dependents(resource) click to toggle source

# File lib/puppet/simple_graph.rb, line 44
def dependents(resource)
  vertex?(resource) ? downstream_from_vertex(resource).keys : []
end

direct_dependencies_of(v) click to toggle source

# File lib/puppet/simple_graph.rb, line 392
def direct_dependencies_of(v)
  (@in_to[v] || {}).keys 
end

direct_dependents_of(v) click to toggle source

# File lib/puppet/simple_graph.rb, line 378
def direct_dependents_of(v)
  (@out_from[v] || {}).keys 
end

directed?() click to toggle source

Whether our graph is directed. Always true. Used to produce dot files.

# File lib/puppet/simple_graph.rb, line 49
def directed?
  true
end

dotty(params = {}, dotfile = 'graph.dot') click to toggle source

Call dotty for the graph which is written to the file ‘graph.dot’ in the # current directory.

# File lib/puppet/simple_graph.rb, line 458
def dotty (params = {}, dotfile = 'graph.dot')
  File.open(dotfile, 'w') {|f| f << to_dot(params) }
  system('dotty', dotfile)
end

downstream_from_vertex(v) click to toggle source

# File lib/puppet/simple_graph.rb, line 368
def downstream_from_vertex(v)
  return @downstream_from[v] if @downstream_from[v]
  result = @downstream_from[v] = {}
  @out_from[v].keys.each do |node|
    result[node] = 1
    result.update(downstream_from_vertex(node))
  end
  result
end

each_edge() { |e| ... } click to toggle source

# File lib/puppet/simple_graph.rb, line 319
def each_edge
  @in_to.each { |t,ns| ns.each { |s,es| es.each { |e| yield e }}}
end

edge?(source, target) click to toggle source

Is there an edge between the two vertices?

# File lib/puppet/simple_graph.rb, line 311
def edge?(source, target)
  vertex?(source) and vertex?(target) and @out_from[source][target]
end

edges() click to toggle source

# File lib/puppet/simple_graph.rb, line 315
def edges
  @in_to.values.collect { |x| x.values }.flatten
end

edges_between(source, target) click to toggle source

Find all matching edges.

# File lib/puppet/simple_graph.rb, line 306
def edges_between(source, target)
  (@out_from[source] || {})[target] || []
end

find_cycles_in_graph() click to toggle source

Find all cycles in the graph by detecting all the strongly connected components, then eliminating everything with a size of one as uninteresting - which it is, because it can’t be a cycle. :)

This has an unhealthy relationship with the ‘tarjan’ method above, which it uses to implement the detection of strongly connected components.

# File lib/puppet/simple_graph.rb, line 160
def find_cycles_in_graph
  state = {
    :number => 0, :index => {}, :lowlink => {}, :scc => [],
    :stack => [], :seen => {}
  }

  # we usually have a disconnected graph, must walk all possible roots
  vertices.each do |vertex|
    if ! state[:index][vertex] then
      tarjan vertex, state
    end
  end

  # To provide consistent results to the user, given that a hash is never
  # assured to return the same order, and given our graph processing is
  # based on hash tables, we need to sort the cycles internally, as well as
  # the set of cycles.
  #
  # Given we are in a failure state here, any extra cost is more or less
  # irrelevant compared to the cost of a fix - which is on a human
  # time-scale.
  state[:scc].select { |c| c.length > 1 }.map {|x| x.sort }.sort
end

instance_variable_get(v) click to toggle source

#instance_variable_get is used by Object#to_zaml to get instance variables. Override it so that we can simulate the presence of instance variables @edges and @vertices for serialization.

Calls superclass method

# File lib/puppet/simple_graph.rb, line 501
def instance_variable_get(v)
  case v.to_s
  when '@edges' then
    edges
  when '@vertices' then
    if self.class.use_new_yaml_format
      vertices
    else
      result = {}
      vertices.each do |vertex|
        adjacencies = {}
        [:in, :out].each do |direction|
          adjacencies[direction] = {}
          adjacent(vertex, :direction => direction, :type => :edges).each do |edge|
            other_vertex = direction == :in ? edge.source : edge.target
            (adjacencies[direction][other_vertex] ||= Set.new).add(edge)
          end
        end
        result[vertex] = Puppet::SimpleGraph::VertexWrapper.new(vertex, adjacencies)
      end
      result
    end
  else
    super(v)
  end
end

leaves(vertex, direction = :out) click to toggle source

Determine all of the leaf nodes below a given vertex.

# File lib/puppet/simple_graph.rb, line 54
def leaves(vertex, direction = :out)
  tree_from_vertex(vertex, direction).keys.find_all { |c| adjacent(c, :direction => direction).empty? }
end

matching_edges(event, base = nil) click to toggle source

Collect all of the edges that the passed events match. Returns an array of edges.

# File lib/puppet/simple_graph.rb, line 60
def matching_edges(event, base = nil)
  source = base || event.resource

  unless vertex?(source)
    Puppet.warning "Got an event from invalid vertex #{source.ref}"
    return []
  end
  # Get all of the edges that this vertex should forward events
  # to, which is the same thing as saying all edges directly below
  # This vertex in the graph.
  @out_from[source].values.flatten.find_all { |edge| edge.match?(event.name) }
end

path_between(f,t) click to toggle source

Return an array of the edge-sets between a series of n+1 vertices (f=v0,v1,v2…t=vn)

connecting the two given verticies.  The ith edge set is an array containing all the
edges between v(i) and v(i+1); these are (by definition) never empty.

  * if f == t, the list is empty
  * if they are adjacent the result is an array consisting of
    a single array (the edges from f to t)
  * and so on by induction on a vertex m between them
  * if there is no path from f to t, the result is nil

This implementation is not particularly efficient; it’s used in testing where clarity

is more important than last-mile efficiency.

# File lib/puppet/simple_graph.rb, line 409
def path_between(f,t)
  if f==t
    []
  elsif direct_dependents_of(f).include?(t)
    [edges_between(f,t)]
  elsif dependents(f).include?(t)
    m = (dependents(f) & direct_dependencies_of(t)).first
    path_between(f,m) + path_between(m,t)
  else
    nil
  end
end

paths_in_cycle(cycle, max_paths = 1) click to toggle source

Perform a BFS on the sub graph representing the cycle, with a view to generating a sufficient set of paths to report the cycle meaningfully, and ideally usefully, for the end user.

BFS is preferred because it will generally report the shortest paths through the graph first, which are more likely to be interesting to the user. I think; it would be interesting to verify that. –daniel 2011-01-23

# File lib/puppet/simple_graph.rb, line 191
def paths_in_cycle(cycle, max_paths = 1)
  raise ArgumentError, "negative or zero max_paths" if max_paths < 1

  # Calculate our filtered outbound vertex lists...
  adj = {}
  cycle.each do |vertex|
    adj[vertex] = adjacent(vertex).select{|s| cycle.member? s}
  end

  found = []

  # frame struct is vertex, [path]
  stack = [[cycle.first, []]]
  while frame = stack.shift do
    if frame[1].member?(frame[0]) then
      found << frame[1] + [frame[0]]
      break if found.length >= max_paths
    else
      adj[frame[0]].each do |to|
        stack.push [to, frame[1] + [frame[0]]]
      end
    end
  end

  return found.sort
end

remove_edge!(e) click to toggle source

Remove an edge from our graph.

# File lib/puppet/simple_graph.rb, line 324
def remove_edge!(e)
  if edge?(e.source,e.target)
    @upstream_from.clear
    @downstream_from.clear
    @in_to   [e.target].delete e.source if (@in_to   [e.target][e.source] -= [e]).empty?
    @out_from[e.source].delete e.target if (@out_from[e.source][e.target] -= [e]).empty?
  end
end

remove_vertex!(v) click to toggle source

Remove a vertex from the graph.

# File lib/puppet/simple_graph.rb, line 270
def remove_vertex!(v)
  return unless vertex?(v)
  @upstream_from.clear
  @downstream_from.clear
  (@in_to[v].values+@out_from[v].values).flatten.each { |e| remove_edge!(e) }
  @in_to.delete(v)
  @out_from.delete(v)
end

report_cycles_in_graph() click to toggle source

# File lib/puppet/simple_graph.rb, line 218
def report_cycles_in_graph
  cycles = find_cycles_in_graph
  n = cycles.length           # where is "pluralize"? --daniel 2011-01-22
  return if n == 0
  s = n == 1 ? '' : 's'

  message = "Found #{n} dependency cycle#{s}:\n"
  cycles.each do |cycle|
    paths = paths_in_cycle(cycle)
    message += paths.map{ |path| '(' + path.join(" => ") + ')'}.join("\n") + "\n"
  end

  if Puppet[:graph] then
    filename = write_cycles_to_graph(cycles)
    message += "Cycle graph written to #{filename}."
  else
    message += "Try the '--graph' option and opening the "
    message += "resulting '.dot' file in OmniGraffle or GraphViz"
  end

  raise Puppet::Error, message
end

reversal() click to toggle source

Return a reversed version of this graph.

# File lib/puppet/simple_graph.rb, line 74
def reversal
  result = self.class.new
  vertices.each { |vertex| result.add_vertex(vertex) }
  edges.each do |edge|
    result.add_edge edge.class.new(edge.target, edge.source, edge.label)
  end
  result
end

size() click to toggle source

Return the size of the graph.

# File lib/puppet/simple_graph.rb, line 84
def size
  vertices.size
end

tarjan(root, s) click to toggle source

This is a simple implementation of Tarjan’s algorithm to find strongly connected components in the graph; this is a fairly ugly implementation, because I can’t just decorate the vertices themselves.

This method has an unhealthy relationship with the #find_cycles_in_graph method below, which contains the knowledge of how the state object is maintained.

# File lib/puppet/simple_graph.rb, line 99
def tarjan(root, s)
  # initialize the recursion stack we use to work around the nasty lack of a
  # decent Ruby stack.
  recur = [{ :node => root }]

  while not recur.empty? do
    frame = recur.last
    vertex = frame[:node]

    case frame[:step]
    when nil then
      s[:index][vertex]   = s[:number]
      s[:lowlink][vertex] = s[:number]
      s[:number]          = s[:number] + 1

      s[:stack].push(vertex)
      s[:seen][vertex] = true

      frame[:children] = adjacent(vertex)
      frame[:step]     = :children

    when :children then
      if frame[:children].length > 0 then
        child = frame[:children].shift
        if ! s[:index][child] then
          # Never seen, need to recurse.
          frame[:step] = :after_recursion
          frame[:child] = child
          recur.push({ :node => child })
        elsif s[:seen][child] then
          s[:lowlink][vertex] = [s[:lowlink][vertex], s[:index][child]].min
        end
      else
        if s[:lowlink][vertex] == s[:index][vertex] then
          this_scc = []
          begin
            top = s[:stack].pop
            s[:seen][top] = false
            this_scc << top
          end until top == vertex
          s[:scc] << this_scc
        end
        recur.pop               # done with this node, finally.
      end

    when :after_recursion then
      s[:lowlink][vertex] = [s[:lowlink][vertex], s[:lowlink][frame[:child]]].min
      frame[:step] = :children

    else
      fail "#{frame[:step]} is an unknown step"
    end
  end
end

to_a() click to toggle source

# File lib/puppet/simple_graph.rb, line 88
def to_a
  vertices
end

to_dot(params={}) click to toggle source

Output the dot format as a string

# File lib/puppet/simple_graph.rb, line 454
def to_dot (params={}) to_dot_graph(params).to_s; end

to_dot_graph(params = {}) click to toggle source

Return a DOT::DOTDigraph for directed graphs or a DOT::DOTSubgraph for an undirected Graph. params can contain any graph property specified in rdot.rb. If an edge or vertex label is a kind of Hash then the keys which match dot properties will be used as well.

# File lib/puppet/simple_graph.rb, line 428
def to_dot_graph (params = {})
  params['name'] ||= self.class.name.gsub(/:/,'_')
  fontsize   = params['fontsize'] ? params['fontsize'] : '8'
  graph      = (directed? ? DOT::DOTDigraph : DOT::DOTSubgraph).new(params)
  edge_klass = directed? ? DOT::DOTDirectedEdge : DOT::DOTEdge
  vertices.each do |v|
    name = v.to_s
    params = {'name'     => '"'+name+'"',
      'fontsize' => fontsize,
      'label'    => name}
    v_label = v.to_s
    params.merge!(v_label) if v_label and v_label.kind_of? Hash
    graph << DOT::DOTNode.new(params)
  end
  edges.each do |e|
    params = {'from'     => '"'+ e.source.to_s + '"',
      'to'       => '"'+ e.target.to_s + '"',
      'fontsize' => fontsize }
    e_label = e.to_s
    params.merge!(e_label) if e_label and e_label.kind_of? Hash
    graph << edge_klass.new(params)
  end
  graph
end

to_yaml_properties() click to toggle source

# File lib/puppet/simple_graph.rb, line 528
def to_yaml_properties
  (instance_variables + [:@vertices, :@edges] -
   [:@in_to, :@out_from, :@upstream_from, :@downstream_from]).uniq
end

tree_from_vertex(start, direction = :out) click to toggle source

A different way of walking a tree, and a much faster way than the one that comes with GRATR.

# File lib/puppet/simple_graph.rb, line 360
def tree_from_vertex(start, direction = :out)
  predecessor={}
  walk(start, direction) do |parent, child|
    predecessor[child] = parent
  end
  predecessor
end

upstream_from_vertex(v) click to toggle source

# File lib/puppet/simple_graph.rb, line 382
def upstream_from_vertex(v)
  return @upstream_from[v] if @upstream_from[v]
  result = @upstream_from[v] = {}
  @in_to[v].keys.each do |node|
    result[node] = 1
    result.update(upstream_from_vertex(node))
  end
  result
end

vertex?(v) click to toggle source

Test whether a given vertex is in the graph.

# File lib/puppet/simple_graph.rb, line 280
def vertex?(v)
  @in_to.include?(v)
end

vertices() click to toggle source

Return a list of all vertices.

# File lib/puppet/simple_graph.rb, line 285
def vertices
  @in_to.keys
end

walk(source, direction) { |node, target| ... } click to toggle source

Just walk the tree and pass each edge.

# File lib/puppet/simple_graph.rb, line 340
def walk(source, direction)
  # Use an iterative, breadth-first traversal of the graph. One could do
  # this recursively, but Ruby's slow function calls and even slower
  # recursion make the shorter, recursive algorithm cost-prohibitive.
  stack = [source]
  seen = Set.new
  until stack.empty?
    node = stack.shift
    next if seen.member? node
    connected = adjacent(node, :direction => direction)
    connected.each do |target|
      yield node, target
    end
    stack.concat(connected)
    seen << node
  end
end

write_cycles_to_graph(cycles) click to toggle source

# File lib/puppet/simple_graph.rb, line 241
def write_cycles_to_graph(cycles)
  # This does not use the DOT graph library, just writes the content
  # directly.  Given the complexity of this, there didn't seem much point
  # using a heavy library to generate exactly the same content. --daniel 2011-01-27
  Puppet.settings.use(:graphing)

  graph = ["digraph Resource_Cycles {"]
  graph << '  label = "Resource Cycles"'

  cycles.each do |cycle|
    paths_in_cycle(cycle, 10).each do |path|
      graph << path.map { |v| '"' + v.to_s.gsub(/"/, '\"') + '"' }.join(" -> ")
    end
  end

  graph << '}'

  filename = File.join(Puppet[:graphdir], "cycles.dot")
  File.open(filename, "w") { |f| f.puts graph }
  return filename
end

write_graph(name) click to toggle source

Produce the graph files if requested.

# File lib/puppet/simple_graph.rb, line 464
def write_graph(name)
  return unless Puppet[:graph]

  Puppet.settings.use(:graphing)

  file = File.join(Puppet[:graphdir], "#{name}.dot")
  File.open(file, "w") { |f|
    f.puts to_dot("name" => name.to_s.capitalize)
  }
end

yaml_initialize(tag, var) click to toggle source

# File lib/puppet/simple_graph.rb, line 533
def yaml_initialize(tag, var)
  initialize()
  vertices = var.delete('vertices')
  edges = var.delete('edges')
  if vertices.is_a?(Hash)
    # Support old (2.6) format
    vertices = vertices.keys
  end
  vertices.each { |v| add_vertex(v) }
  edges.each { |e| add_edge(e) }
  var.each do |varname, value|
    instance_variable_set("@#{varname}", value)
  end
end