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

Class EmptyTraversalSideEffects

java.lang.Object

org.apache.tinkerpop.gremlin.process.traversal.util.EmptyTraversalSideEffects

All Implemented Interfaces:

Serializable, Cloneable, TraversalSideEffects

public final class EmptyTraversalSideEffects
extends Object
implements TraversalSideEffects

Author:

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

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.tinkerpop.gremlin.process.traversal.TraversalSideEffects

TraversalSideEffects.Exceptions

Method Summary

Modifier and Type	Method and Description
void	add(String key, Object value) Add a value to the global side-effect value.
TraversalSideEffects	clone() Cloning is used to duplicate the sideEffects typically in distributed execution environments.
<V> V	get(String key) Get the sideEffect associated with the provided key.
<V> BinaryOperator<V>	getReducer(String key) Get the reducer associated with the side-effect key.
<V> Optional<Supplier<V>>	getRegisteredSupplier(String key) Get the registered Supplier associated with the specified key.
<S> Supplier<S>	getSackInitialValue() If sacks are enabled, get the initial value of the Traverser sack.
<S> BinaryOperator<S>	getSackMerger() If sacks are enabled and a merge function has been specified, then get it (else get null).
<S> UnaryOperator<S>	getSackSplitter() If sacks are enabled and a split operator has been specified, then get it (else get null).
<V> Supplier<V>	getSupplier(String key) Get the supplier associated with the side-effect key.
static EmptyTraversalSideEffects	instance()
Set<String>	keys() The keys of the sideEffect which includes registered Supplier keys.
void	mergeInto(TraversalSideEffects sideEffects) Add the current TraversalSideEffects values, suppliers, and reducers to the provided TraversalSideEffects.
<V> void	register(String key, Supplier<V> initialValue, BinaryOperator<V> reducer) Register a side-effect with the TraversalSideEffects providing a Supplier and a BinaryOperator.
<V> void	registerIfAbsent(String key, Supplier<V> initialValue, BinaryOperator<V> reducer) Register a side-effect with the TraversalSideEffects providing a Supplier and a BinaryOperator.
void	registerSupplier(String key, Supplier supplier) Register a Supplier with the provided key.
void	remove(String key) Remove both the value and registered Supplier associated with provided key.
void	set(String key, Object value) Set the specified key to the specified value.
<S> void	setSack(Supplier<S> initialValue, UnaryOperator<S> splitOperator, BinaryOperator<S> mergeOperator) Set the initial value of each Traverser "sack" along with the operators for splitting and merging sacks.

Methods inherited from class java.lang.Object

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

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

exists, forEach, getOrCreate, registerSupplierIfAbsent

Method Detail

set

public void set(String key,
                Object value)
         throws IllegalArgumentException

Description copied from interface: TraversalSideEffects

Set the specified key to the specified value. This method should not be used in a distributed environment. Instead, use TraversalSideEffects.add(String, Object). This method is only safe when there is only one representation of the side-effect and thus, not distributed across threads or machines.

Specified by:

set in interface TraversalSideEffects

Parameters:

key - the key they key of the side-effect

value - the value the new value for the side-effect

Throws:

IllegalArgumentException - if the key does not reference a registered side-effect.

get

public <V> V get(String key)
          throws IllegalArgumentException

Description copied from interface: TraversalSideEffects

Get the sideEffect associated with the provided key. If the sideEffect contains an object for the key, return it. Else if the sideEffect has a registered Supplier for that key, generate the object, store the object in the sideEffects, and return it.

Specified by:

get in interface TraversalSideEffects

Type Parameters:

V - the type of the value to retrieve

Parameters:

key - the key to get the value for

Returns:

the value associated with key

Throws:

IllegalArgumentException - if the key does not reference an object or a registered supplier.

remove

public void remove(String key)
            throws IllegalArgumentException

Description copied from interface: TraversalSideEffects

Remove both the value and registered Supplier associated with provided key.

Specified by:

remove in interface TraversalSideEffects

Parameters:

key - the key of the value and registered supplier to remove

Throws:

IllegalArgumentException

keys

public Set<String> keys()

Description copied from interface: TraversalSideEffects

The keys of the sideEffect which includes registered Supplier keys. In essence, that which is possible to get().

Specified by:

keys in interface TraversalSideEffects

Returns:

the keys of the sideEffect

add

public void add(String key,
                Object value)
         throws IllegalArgumentException

Description copied from interface: TraversalSideEffects

Add a value to the global side-effect value. This should be used by steps to ensure that side-effects are merged properly in a distributed environment. TraversalSideEffects.set(String, Object) should only be used in single-threaded systems or by a master traversal in a distributed environment.

Specified by:

add in interface TraversalSideEffects

Parameters:

key - the key of the side-effect.

value - the partital value (to be merged) of the side-effect.

Throws:

IllegalArgumentException - if no side-effect exists for the provided key

register

public <V> void register(String key,
                         Supplier<V> initialValue,
                         BinaryOperator<V> reducer)

Description copied from interface: TraversalSideEffects

Register a side-effect with the TraversalSideEffects providing a Supplier and a BinaryOperator. If a null value is provided for the supplier or reducer, then it no supplier or reducer is registered.

Specified by:

register in interface TraversalSideEffects

Type Parameters:

V - the type of the side-effect value

Parameters:

key - the key of the side-effect value

initialValue - the initial value supplier

reducer - the reducer to use for merging a distributed side-effect value into a single value

registerIfAbsent

public <V> void registerIfAbsent(String key,
                                 Supplier<V> initialValue,
                                 BinaryOperator<V> reducer)

Description copied from interface: TraversalSideEffects

Register a side-effect with the TraversalSideEffects providing a Supplier and a BinaryOperator. The registration will only overwrite a supplier or reducer if no supplier or reducer existed prior. If a null value is provided for the supplier or reducer, then it no supplier or reducer is registered.

Specified by:

registerIfAbsent in interface TraversalSideEffects

Type Parameters:

V - the type of the side-effect value

Parameters:

key - the key of the side-effect value

initialValue - the initial value supplier

reducer - the reducer to use for merging a distributed side-effect value into a single value

getReducer

public <V> BinaryOperator<V> getReducer(String key)
                                 throws IllegalArgumentException

Description copied from interface: TraversalSideEffects

Get the reducer associated with the side-effect key. If no reducer was registered, then Operator.assign is provided.

Specified by:

getReducer in interface TraversalSideEffects

Type Parameters:

V - the type of the side-effect value

Parameters:

key - the key of the side-effect

Returns:

the registered reducer

Throws:

IllegalArgumentException - if no side-effect exists for the provided key

getSupplier

public <V> Supplier<V> getSupplier(String key)
                            throws IllegalArgumentException

Description copied from interface: TraversalSideEffects

Get the supplier associated with the side-effect key. If no supplier was registered, then ConstantSupplier is provided.

Specified by:

getSupplier in interface TraversalSideEffects

Type Parameters:

V - the type of the side-effect value

Parameters:

key - the key of the side-effect

Returns:

the registered supplier

Throws:

IllegalArgumentException - if no side-effect exists for the provided key

registerSupplier

public void registerSupplier(String key,
                             Supplier supplier)

Description copied from interface: TraversalSideEffects

Register a Supplier with the provided key. When sideEffects get() are called, if no object exists and there exists a registered supplier for the key, the object is generated. Registered suppliers are used for the lazy generation of sideEffect data.

Specified by:

registerSupplier in interface TraversalSideEffects

Parameters:

key - the key to register the supplier with

supplier - the supplier that will generate an object when get() is called if it hasn't already been created

getRegisteredSupplier

public <V> Optional<Supplier<V>> getRegisteredSupplier(String key)

Description copied from interface: TraversalSideEffects

Get the registered Supplier associated with the specified key.

Specified by:

getRegisteredSupplier in interface TraversalSideEffects

Type Parameters:

V - The object type of the supplier

Parameters:

key - the key associated with the supplier

Returns:

A non-empty optional if the supplier exists

setSack

public <S> void setSack(Supplier<S> initialValue,
                        UnaryOperator<S> splitOperator,
                        BinaryOperator<S> mergeOperator)

Description copied from interface: TraversalSideEffects

Set the initial value of each Traverser "sack" along with the operators for splitting and merging sacks. If no split operator is provided, then a direct memory copy is assumed (this is typically good for primitive types and strings). If no merge operator is provided, then traversers with sacks will not be merged.

Specified by:

setSack in interface TraversalSideEffects

Type Parameters:

S - the sack type

Parameters:

initialValue - the initial value supplier of the traverser sack

splitOperator - the split operator for splitting traverser sacks

mergeOperator - the merge operator for merging traverser sacks

getSackInitialValue

public <S> Supplier<S> getSackInitialValue()

Description copied from interface: TraversalSideEffects

If sacks are enabled, get the initial value of the Traverser sack. If its not enabled, then null is returned.

Specified by:

getSackInitialValue in interface TraversalSideEffects

Type Parameters:

S - the sack type

Returns:

the supplier of the initial value of the traverser sack

getSackSplitter

public <S> UnaryOperator<S> getSackSplitter()

Description copied from interface: TraversalSideEffects

If sacks are enabled and a split operator has been specified, then get it (else get null). The split operator is used to split a sack when a bifurcation in a Traverser happens.

Specified by:

getSackSplitter in interface TraversalSideEffects

Type Parameters:

S - the sack type

Returns:

the operator for splitting a traverser sack

getSackMerger

public <S> BinaryOperator<S> getSackMerger()

Description copied from interface: TraversalSideEffects

If sacks are enabled and a merge function has been specified, then get it (else get null). The merge function is used to merge two sacks when two Traversers converge.

Specified by:

getSackMerger in interface TraversalSideEffects

Type Parameters:

S - the sack type

Returns:

the operator for merging two traverser sacks

clone

public TraversalSideEffects clone()

Description copied from interface: TraversalSideEffects

Cloning is used to duplicate the sideEffects typically in distributed execution environments.

Specified by:

clone in interface TraversalSideEffects

Overrides:

clone in class Object

Returns:

The cloned sideEffects

mergeInto

public void mergeInto(TraversalSideEffects sideEffects)

Description copied from interface: TraversalSideEffects

Add the current TraversalSideEffects values, suppliers, and reducers to the provided TraversalSideEffects. The implementation should (under the hood), use TraversalSideEffects.registerIfAbsent(String, Supplier, BinaryOperator) so that if the argument TraversalSideEffects already has a registered supplier or binary operator, then don't overwrite it.

Specified by:

mergeInto in interface TraversalSideEffects

Parameters:

sideEffects - the sideEffects to add this traversal's sideEffect data to.

instance

public static EmptyTraversalSideEffects instance()