Package org.apache.tinkerpop.gremlin.process.traversal.step.util

Class ReducingBarrierStep<S,E>

java.lang.Object

org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep<S,E>

org.apache.tinkerpop.gremlin.process.traversal.step.util.ReducingBarrierStep<S,E>

All Implemented Interfaces:

Serializable, Cloneable, Iterator<Traverser.Admin<E>>, Step<S,E>, Barrier<E>, Generating<E,E>, MemoryComputing<E>

Direct Known Subclasses:

CountGlobalStep, FoldStep, GroupCountStep, GroupStep, MaxGlobalStep, MeanGlobalStep, MinGlobalStep, SumGlobalStep, TreeStep

public abstract class ReducingBarrierStep<S,E>
extends AbstractStep<S,E>
implements Barrier<E>, Generating<E,E>

Author:

Marko A. Rodriguez (http://markorodriguez.com)

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	ReducingBarrierStep.NonEmittingSeed	A class that represents a value that is not be to be emitted which helps with flow control internal to the class and is serializable in Gryo for use in OLAP.

Field Summary

Fields

Modifier and Type	Field	Description
protected boolean	hasProcessedOnce
static Object	NON_EMITTING_SEED	A seed value not to be emitted from the ReducingBarrierStep helping with flow control within this step.
protected BinaryOperator<E>	reducingBiOperator
protected Supplier<E>	seedSupplier	If the seedSupplier is null then the default behavior is to generate the seed from the starts.

Fields inherited from class org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep

id, labels, nextEnd, nextStep, previousStep, starts, traversal, traverserStepIdAndLabelsSetByChild

Constructor Summary

Constructors

Constructor	Description
ReducingBarrierStep(Traversal.Admin traversal)

Method Summary

Modifier and Type	Method	Description
void	addBarrier(E barrier)	Add a barrier to the step.
ReducingBarrierStep<S,E>	clone()	Cloning is used to duplicate steps for the purpose of traversal optimization and OLTP replication.
void	done()	A way to hard set that the barrier is complete.
protected E	generateSeedFromStarts()	If the seedSupplier is null then this method is called.
BinaryOperator<E>	getBiOperator()
MemoryComputeKey<E>	getMemoryComputeKey()	The MemoryComputeKey that will be used by this step.
Supplier<E>	getSeedSupplier()	Gets the provided seed supplier or provides generateSeedFromStarts().
boolean	hasNextBarrier()	Whether or not the step has an accessible barrier.
E	nextBarrier()	Get the next barrier within this step.
void	processAllStarts()	Process all left traversers by do not yield the resultant output.
Traverser.Admin<E>	processNextStart()
abstract E	projectTraverser(Traverser.Admin<S> traverser)
void	reset()	Reset the state of the step such that it has no incoming starts.
void	setReducingBiOperator(BinaryOperator<E> reducingBiOperator)
void	setSeedSupplier(Supplier<E> seedSupplier)

Methods inherited from class org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep

addLabel, addStart, addStarts, equals, getId, getLabels, getNextStep, getPreviousStep, getStarts, getTraversal, hashCode, hasNext, hasStarts, isTraverserStepIdAndLabelsSetByChild, next, prepareTraversalForNextStep, removeLabel, setId, setNextStep, setPreviousStep, setTraversal, toString

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface org.apache.tinkerpop.gremlin.process.traversal.step.Generating

generateFinalResult

Methods inherited from interface java.util.Iterator

forEachRemaining, remove

Methods inherited from interface org.apache.tinkerpop.gremlin.process.traversal.Step

equals, getRequirements

Field Detail

NON_EMITTING_SEED

public static final Object NON_EMITTING_SEED

A seed value not to be emitted from the ReducingBarrierStep helping with flow control within this step.

seedSupplier

protected Supplier<E> seedSupplier

If the seedSupplier is null then the default behavior is to generate the seed from the starts. This supplier must be callable as a constant and not rely on state from the class. Prefer overriding generateSeedFromStarts() otherwise.

reducingBiOperator

protected BinaryOperator<E> reducingBiOperator

hasProcessedOnce

protected boolean hasProcessedOnce

Constructor Detail

ReducingBarrierStep

public ReducingBarrierStep(Traversal.Admin traversal)

Method Detail

setSeedSupplier

public void setSeedSupplier(Supplier<E> seedSupplier)

getSeedSupplier

public Supplier<E> getSeedSupplier()

Gets the provided seed supplier or provides generateSeedFromStarts().

generateSeedFromStarts

protected E generateSeedFromStarts()

If the seedSupplier is null then this method is called.

projectTraverser

public abstract E projectTraverser(Traverser.Admin<S> traverser)

setReducingBiOperator

public void setReducingBiOperator(BinaryOperator<E> reducingBiOperator)

getBiOperator

public BinaryOperator<E> getBiOperator()

reset

public void reset()

Description copied from interface: Step

Reset the state of the step such that it has no incoming starts. Internal states are to be reset, but any sideEffect data structures are not to be recreated.

Specified by:

reset in interface Step<S,E>

Overrides:

reset in class AbstractStep<S,E>

done

public void done()

Description copied from interface: Barrier

A way to hard set that the barrier is complete. This is necessary when parallel barriers don't all have barriers and need hard resetting. The default implementation does nothing.

Specified by:

done in interface Barrier<S>

processAllStarts

public void processAllStarts()

Description copied from interface: Barrier

Process all left traversers by do not yield the resultant output. This method is useful for steps like ReducingBarrierStep, where traversers can be processed "on the fly" and thus, reduce memory consumption.

Specified by:

processAllStarts in interface Barrier<S>

hasNextBarrier

public boolean hasNextBarrier()

Description copied from interface: Barrier

Whether or not the step has an accessible barrier.

Specified by:

hasNextBarrier in interface Barrier<S>

Returns:

whether a barrier exists or not

nextBarrier

public E nextBarrier()

Description copied from interface: Barrier

Get the next barrier within this step. Barriers from parallel steps can be the be merged to create a single step with merge barriers.

Specified by:

nextBarrier in interface Barrier<S>

Returns:

the next barrier of the step

addBarrier

public void addBarrier(E barrier)

Description copied from interface: Barrier

Add a barrier to the step. This typically happens when multiple parallel barriers need to become one barrier at a single step.

Specified by:

addBarrier in interface Barrier<S>

Parameters:

barrier - the barrier to merge in

processNextStart

public Traverser.Admin<E> processNextStart()

Specified by:

processNextStart in class AbstractStep<S,E>

clone

public ReducingBarrierStep<S,E> clone()

Description copied from interface: Step

Cloning is used to duplicate steps for the purpose of traversal optimization and OLTP replication. When cloning a step, it is important that the steps, the cloned step is equivalent to the state of the step when Step.reset() is called. Moreover, the previous and next steps should be set to EmptyStep.

Specified by:

clone in interface Step<S,E>

Overrides:

clone in class AbstractStep<S,E>

Returns:

The cloned step

getMemoryComputeKey

public MemoryComputeKey<E> getMemoryComputeKey()

Description copied from interface: MemoryComputing

The MemoryComputeKey that will be used by this step.

Specified by:

getMemoryComputeKey in interface MemoryComputing<S>

Returns:

the MemoryComputeKey to use