org.apache.pig.impl.plan
Class DependencyOrderWalker<O extends Operator,P extends OperatorPlan<O>>

java.lang.Object
  org.apache.pig.impl.plan.PlanWalker<O,P>
      org.apache.pig.impl.plan.DependencyOrderWalker<O,P>

public class DependencyOrderWalker<O extends Operator,P extends OperatorPlan<O>>
extends PlanWalker<O,P>

DependencyOrderWalker traverses the graph in such a way that no node is visited before all the nodes it depends on have been visited. Beyond this, it does not guarantee any particular order. So, you have a graph with node 1 2 3 4, and edges 1->3, 2->3, and 3->4, this walker guarnatees that 1 and 2 will be visited before 3 and 3 before 4, but it does not guarantee whether 1 or 2 will be visited first.

Field Summary

Fields inherited from class org.apache.pig.impl.plan.PlanWalker

mPlan

Constructor Summary

DependencyOrderWalker(P plan)

Method Summary

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

Methods inherited from class org.apache.pig.impl.plan.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(P plan)

Parameters:

plan - Plan for this walker to traverse.

Method Detail

walk

public void walk(PlanVisitor<O,P> visitor)
          throws VisitorException

Begin traversing the graph.

Specified by:

walk in class PlanWalker<O extends Operator,P extends OperatorPlan<O>>

Parameters:

visitor - Visitor this walker is being used by.

Throws:

VisitorException - if an error is encountered while walking.

spawnChildWalker

public PlanWalker<O,P> spawnChildWalker(P 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<O extends Operator,P extends OperatorPlan<O>>

Parameters:

plan - Plan for the new walker.

Returns:

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

doAllPredecessors

protected void doAllPredecessors(O node,
                                 Set<O> seen,
                                 Collection<O> fifo)
                          throws VisitorException

Throws:

VisitorException