org.apache.pig.newplan
Class DependencyOrderWalker

java.lang.Object
  org.apache.pig.newplan.PlanWalker
      org.apache.pig.newplan.DependencyOrderWalker

Direct Known Subclasses:

SubtreeDependencyOrderWalker

public class DependencyOrderWalker
extends PlanWalker

A walker to walk graphs in dependency order. It is guaranteed that a node will not be visited until all of its predecessors have been visited. This is equivalent to doing a topilogical sort on the graph and then visiting the nodes in order.

Field Summary

Fields inherited from class org.apache.pig.newplan.PlanWalker

plan

Constructor Summary

DependencyOrderWalker(OperatorPlan plan)

Method Summary

protected void	doAllPredecessors(Operator node, Set<Operator> seen, Collection<Operator> fifo)
PlanWalker	spawnChildWalker(OperatorPlan plan) Return a new instance of this same type of walker for a subplan.
void	walk(PlanVisitor visitor) Begin traversing the graph.

Methods inherited from class org.apache.pig.newplan.PlanWalker

getPlan, setPlan

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DependencyOrderWalker

public DependencyOrderWalker(OperatorPlan plan)

Parameters:

plan - for this walker to traverse.

Method Detail

spawnChildWalker

public PlanWalker spawnChildWalker(OperatorPlan plan)

Description copied from class: PlanWalker

Return a new instance of this same type of walker for a subplan. When this method is called the same type of walker with the provided plan set as the plan, must be returned. This can then be used to walk subplans. This allows abstract visitors to clone walkers without knowning the type of walker their subclasses used.

Specified by:

spawnChildWalker in class PlanWalker

Parameters:

plan - Plan for the new walker.

Returns:

Instance of the same type of walker with plan set to plan.

walk

public void walk(PlanVisitor visitor)
          throws FrontendException

Begin traversing the graph.

Specified by:

walk in class PlanWalker

Parameters:

visitor - Visitor this walker is being used by.

Throws:

VisitorException - if an error is encountered while walking.

FrontendException

doAllPredecessors

protected void doAllPredecessors(Operator node,
                                 Set<Operator> seen,
                                 Collection<Operator> fifo)
                          throws FrontendException

Throws:

FrontendException