com.saxonica.ee.stream.watch

Class ForEachGroupParallelAction

java.lang.Object

com.saxonica.ee.stream.feed.ItemFeed

com.saxonica.ee.stream.watch.ForEachAction

com.saxonica.ee.stream.watch.ForEachGroupParallelAction

All Implemented Interfaces:

Feed

public class ForEachGroupParallelAction
extends ForEachAction

This watch implements xsl:for-each-group in streaming mode, in cases where the population is being forked (using group-by), and where the population is not grounded. The general idea here is that each item is processed as it is encountered, by sending it to an agent which is responsible for processing the group that it belongs to. This means that the processing of different groups is interleaved (they are processed in parallel, though not actually in separate threads). On completion, the outputs from each of the per-group agents are concatenated in order. The memory needed for this process is the amount needed to hold the output of the xsl:for-each-group instruction; the strategy is only really effective in cases where this is significantly less than the memory needed to hold the input. One case where this definitely applies is where the body of the xsl:for-each-group is a call to xsl:result-document; another is where the grouping action does aggregation, e.g. count(current-group()) or sum(current-group()). Although this class inherits from ForEachAction, it does not use all the functionality of the superclass. In particular, it is not capable of handling overlapping nodes in the population.

Nested Class Summary

Nested classes/interfaces inherited from class com.saxonica.ee.stream.watch.ForEachAction

ForEachAction.Activation

Field Summary

Fields inherited from class com.saxonica.ee.stream.watch.ForEachAction

bodyContext

Constructor Summary

Constructors

Constructor and Description
ForEachGroupParallelAction(WatchManager watchManager, ForEachGroup expression, Feed result, XPathContext context)

Method Summary

Modifier and Type	Method and Description
void	close() Finish evaluating the expression.
void	endSelectedParentNode(Location locationId) Signal that the endElement event has occurred for the element whose startElement event caused the Watch to be activated.
void	open(Terminator terminator) Start evaluating the expression.
void	processItem(Item<?> node) Signal that an item (other than an element) that matches the selection has been found.
Receiver	startSelectedParentNode(FleetingParentNode node, Location locationId) Signal that an element (or document node) has been found that matches the selection that this Watch is looking for.

Methods inherited from class com.saxonica.ee.stream.watch.ForEachAction

getAction, getActivationStack, getBodyContext, getInversion, getReceiver, getValuesAwaitingOutput, getWatchManager, isActionConsuming, makeBodyContext, setInversion

Methods inherited from class com.saxonica.ee.stream.feed.ItemFeed

dynamicError, getContext, getExpression, getPipelineConfiguration, getResult, getTerminator, hasFailed, processItems, setExpression, setHasFailed, setPipelineConfiguration, setTerminator

Methods inherited from class java.lang.Object

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

Constructor Detail

ForEachGroupParallelAction

public ForEachGroupParallelAction(WatchManager watchManager,
                                  ForEachGroup expression,
                                  Feed result,
                                  XPathContext context)

Method Detail

open

public void open(Terminator terminator)
          throws XPathException

Description copied from class: ItemFeed

Start evaluating the expression. The default implementation does nothing.

Specified by:

open in interface Feed

Overrides:

open in class ForEachAction

Parameters:

terminator - used to achieve early exit

Throws:

XPathException - if a dynamic error occurs

startSelectedParentNode

public Receiver startSelectedParentNode(FleetingParentNode node,
                                        Location locationId)
                                 throws XPathException

Signal that an element (or document node) has been found that matches the selection that this Watch is looking for. This method is called by the WatchManager while processing the startElement event that matches the selection. For this purpose, any attributes selected by the last step in the selection are ignored

Specified by:

startSelectedParentNode in interface Feed

Overrides:

startSelectedParentNode in class ForEachAction

Parameters:

node - the element or document node whose start event has been matched

locationId - the location associated with the element or document node (may be the location of the instruction that created it)

Returns:

a Receiver to be notified of all events starting with the startElement/startDocument event for the matched element, and ending with the endElement event for that element; or null if this feature is not required.

Throws:

XPathException - if a dynamic error occurs while processing the start-element event

processItem

public void processItem(Item<?> node)
                 throws XPathException

Signal that an item (other than an element) that matches the selection has been found.

Specified by:

processItem in interface Feed

Overrides:

processItem in class ForEachAction

Parameters:

node - the item that was matched.

Throws:

XPathException - May be raised if a dynamic error occurs

endSelectedParentNode

public void endSelectedParentNode(Location locationId)
                           throws XPathException

Signal that the endElement event has occurred for the element whose startElement event caused the Watch to be activated.

Specified by:

endSelectedParentNode in interface Feed

Overrides:

endSelectedParentNode in class ForEachAction

Parameters:

locationId - the location of the node in the source, or of the instruction that created it

Throws:

ValidationException - May be raised if the constraint implemented by this Watch is violated @param locationId the location of the node in the source, or of the instruction that created it

XPathException - May be raised if a constraint implemented by this Watch is violated

close

public void close()
           throws XPathException

Description copied from class: ItemFeed

Finish evaluating the expression. The default implementation does nothing.

Specified by:

close in interface Feed

Overrides:

close in class ForEachAction

Throws:

XPathException - if a dynamic error occurs