com.twitter.cassovary.graph.Traverser.scala Maven / Gradle / Ivy
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/*
* Copyright 2012 Twitter, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this
* file except in compliance with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed
* under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
* CONDITIONS OF ANY KIND, either express or implied. See the License for the
* specific language governing permissions and limitations under the License.
*/
package com.twitter.cassovary.graph
import com.twitter.cassovary.graph.GraphDir._
import com.twitter.cassovary.graph.GraphUtils.RandomWalkParams
import com.twitter.cassovary.graph.tourist.{IntInfoKeeper, PrevNbrCounter}
import com.twitter.ostrich.stats.Stats
import it.unimi.dsi.fastutil.ints.IntArrayList
import it.unimi.dsi.fastutil.objects.ObjectArrayList
import net.lag.logging.Logger
import scala.collection.mutable
import scala.util.Random
/**
* A Traverser traverses the graph in a certain order of nodes.
*/
trait Traverser extends Iterator[Node] { self =>
/**
* Traverser only visits node Ids listed in some node's edges, and thus
* we know that node must exist, safe to assume graph.getNodeById return non-None value
*/
protected def getExistingNodeById(graph: Graph, id: Int) = graph.getNodeById(id).get
}
/**
* Bounds an iterator to go no more than a specified maximum number of steps
*/
trait BoundedIterator[T] extends { private var numStepsTaken = 0L } with Iterator[T] {
val maxSteps: Long
abstract override def next = {
numStepsTaken += 1
super.next
}
abstract override def hasNext = ( (numStepsTaken < maxSteps) && super.hasNext)
}
/**
* Randomly traverse the graph, going from one node to a random neighbor in direction {@code dir}.
* @param graph the graph to traverse on
* @param dir direction in which to traverse
* @param homeNodeIds the ids of nodes that the traverser will go to next if the node has no
* neighbors, or we reset the traversal with probability {@code resetProbability},
* or if the number of out-going edges at the current node exceeds {@code maxNumEdgesThresh}
* @param resetProbability the probability of teleporting back to home node set at each step
* @param maxNumEdgesThresh if set, do not traverse edges with > maxNumEdgesThresh outgoing edges
* @param onlyOnce specifies whether the same node should only be allowed to be visited once
* in any path.
* @param randNumGen a random number generator (for stable walk, a seeded random number
* generator is used).
* @param maxDepth if set, max depth of path
* @param filterHomeNodeByNumEdges filter home node by number of edges
*/
class RandomTraverser(graph: Graph, dir: GraphDir, homeNodeIds: Seq[Int],
resetProbability: Double, maxNumEdgesThresh: Option[Int], onlyOnce: Boolean,
randNumGen: Random, maxDepth: Option[Int], filterHomeNodeByNumEdges: Boolean)
extends Traverser { self =>
private var currNode: Node = null
private var homeNode: Node = null
private val homeNodeIdSet = Set(homeNodeIds: _*)
private val seenNodesTracker = new IntInfoKeeper(self.onlyOnce)
protected def seenBefore(id: Int) = seenNodesTracker.infoOfNode(id).isDefined
private var pathLength = 0
private def goHome(): Int = {
pathLength = 0
NodeUtils.pickRandNodeId(homeNodeIds, randNumGen)
}
private def takeRandomStep(): Int = {
val nextRandom = randNumGen.nextDouble()
val needToFilterByNumEdges = (filterHomeNodeByNumEdges || !(homeNodeIdSet contains currNode.id))
if (nextRandom < resetProbability ||
(needToFilterByNumEdges && NodeUtils.hasTooManyEdges(dir, maxNumEdgesThresh)(currNode))) {
goHome()
} else {
currNode.randomNeighbor(dir, randNumGen).getOrElse(goHome())
}
}
def next = {
val nextNodeId = if (currNode == null ||
(maxDepth.isDefined && pathLength >= maxDepth.get)) {
goHome()
} else {
var randNextNodeId = takeRandomStep()
if (onlyOnce && seenBefore(randNextNodeId)) {
seenNodesTracker.clear()
goHome()
} else {
randNextNodeId
}
}
seenNodesTracker.recordInfo(nextNodeId, 0)
pathLength += 1
currNode = getExistingNodeById(graph, nextNodeId)
currNode
}
def hasNext = true
}
/**
* Same as RandomTraverser except that the number of steps taken is bounded by {@code maxSteps}
*/
class RandomBoundedTraverser(graph: Graph, dir: GraphDir, homeNodeIds: Seq[Int], val maxSteps: Long,
walkParams: RandomWalkParams) extends RandomTraverser(graph, dir, homeNodeIds,
walkParams.resetProbability, walkParams.maxNumEdgesThresh, walkParams.visitSameNodeOnce,
walkParams.randNumGen, walkParams.maxDepth,
walkParams.filterHomeNodeByNumEdges) with BoundedIterator[Node]
/**
* A traverser that keeps track of distance from homeNodeIds. If {@code onlyOnce} is true,
* the same node is not traversed again.
*/
abstract class DistanceTraverser[T](graph: Graph, homeNodeIds: Seq[Int], onlyOnce: Boolean)
extends Traverser { self =>
private val distanceTracker = new IntInfoKeeper(self.onlyOnce)
protected def init(defaultInfo: T) {
homeNodeIds foreach { id => visitPotentialNode(id, defaultInfo, 0) }
}
protected def visitPotentialNode(id: Int, info: T, dist: Int) {
val seen = seenBefore(id)
if (!(onlyOnce && seen)) {
storeForVisit(id, info)
}
if (!seen) distanceTracker.recordInfo(id, dist)
}
protected def storeForVisit(id: Int, info: T)
protected def seenBefore(id: Int) = distance(id).isDefined
def distance(id: Int) = distanceTracker.infoOfNode(id)
}
/**
* Traverses in breadth-first order. This implies that first all the neighbors of
* {@code homeNodeIds} are visited, then their neighbors, etc.
* @param graph the graph to traverse on
* @param dir direction in which to traverse
* @param homeNodeIds the ids of nodes that the BFS starts
* @param maxDepth the maximum depth of nodes to visit in BFS
* @param maxNumEdgesThresh threshold of the number of neighbors a node can have, if a node has more
* than the threshold value, we skip its children in BFS
* @param maxSteps number of steps in traversal
* @param onlyOnce specifies whether the same node should only be allowed to be
* visited once in any path
* @param prevNbrCounter if set, tracks previous neighbors by occurrence
*/
class BreadthFirstTraverser(graph: Graph, dir: GraphDir, homeNodeIds: Seq[Int],
maxDepth: Option[Int], maxNumEdgesThresh: Option[Int], maxSteps: Long,
onlyOnce: Boolean, prevNbrCounter: Option[PrevNbrCounter])
extends Traverser { self =>
private val log = Logger.get
// the number of items can be enqueued is bounded by maxSteps
// because we never need to enqueue more than maxSteps items
private var numEnqueuedEver = 0L
private val qu = new IntArrayList
private val depthTracker = new IntInfoKeeper(true)
homeNodeIds foreach { id =>
depthTracker.recordInfo(id, 0)
enqueueNeighbors(id, 1)
}
private def visitPotentialNode(id: Int, depth: Int) {
if (!(onlyOnce && seen(id))) {
qu.add(id)
numEnqueuedEver += 1
}
depthTracker.recordInfo(id, depth)
}
private def enqueueNeighbors(nodeId: Int, newDepth: Int) {
val nd = getExistingNodeById(graph, nodeId)
if (maxNumEdgesThresh.isEmpty || (nd.neighborCount(dir) <= maxNumEdgesThresh.get)) {
nd.neighborIds(dir) foreach { id =>
// bound the total number of items that
// can be pushed into the queue by maxSteps
if (numEnqueuedEver < maxSteps) {
visitPotentialNode(id, newDepth)
if (prevNbrCounter.isDefined) {
prevNbrCounter.get.recordInfo(id, nodeId)
}
}
}
}
}
private[graph] def depth(id: Int) = depthTracker.infoOfNode(id)
private def seen(id: Int) = depth(id).isDefined
def next = {
val curr = qu.removeInt(0)
val currDepth = depth(curr).get
val nd = getExistingNodeById(graph, curr)
log.ifTrace { "visiting %d, nbrCount=%d, maxNumEdges=%d, depth=%d".format(curr,
nd.neighborCount(dir), maxNumEdgesThresh.getOrElse(-1), currDepth) }
val newDepth = currDepth + 1
enqueueNeighbors(curr, newDepth)
nd
}
def hasNext = if (qu.isEmpty) {
Stats.incr("bfs_walk_request_exhausted_2nd_degree", 1)
false
} else {
maxDepth.isEmpty || depth(qu.getInt(0)).get <= maxDepth.get
}
}
class DepthFirstTraverser(graph: Graph, dir: GraphDir, homeNodeIds: Seq[Int],
onlyOnce: Boolean)
extends DistanceTraverser[Int](graph, homeNodeIds, onlyOnce) {
// stack keeps a tuple (node, child# of higher node in stack). Hence, top node
// of stack always has child# = -1
case class NodeDesc(val id: Int, val childOff: Int)
private val stack = new ObjectArrayList[NodeDesc]
init(-1)
protected def storeForVisit(id: Int, info: Int) { stack.add(NodeDesc(id, info)) }
private def firstNotYetVisitedNode(nd: Node, off: Int): Option[NodeDesc] = {
assert(off != -1)
if (off == nd.neighborCount(dir)) {
// no more children of this node left, go to its parent
if (stack.isEmpty) None else {
val topel = stack.remove(stack.size - 1)
firstNotYetVisitedNode(getExistingNodeById(graph, topel.id), topel.childOff + 1)
}
} else {
val childId = nd.neighborIds(dir)(off)
if (onlyOnce && seenBefore(childId)) {
// try the next child
firstNotYetVisitedNode(nd, off + 1)
} else {
storeForVisit(nd.id, off)
Some(NodeDesc(childId, distance(nd.id).get + 1))
}
}
}
def next = {
var NodeDesc(id, off) = stack.remove(stack.size - 1)
assert(off == -1)
val topnd = getExistingNodeById(graph, id)
val nextUnvisitedNode = firstNotYetVisitedNode(topnd, off + 1)
nextUnvisitedNode match {
case Some(NodeDesc(nodeId, dist)) => visitPotentialNode(nodeId, -1, dist)
case None => // do nothing
}
topnd
}
def hasNext = !stack.isEmpty
}
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