Package com.saxonica.ee.stream.watch
Class ForEachGroupParallelAction
java.lang.Object
net.sf.saxon.event.Outputter
net.sf.saxon.event.ProxyOutputter
com.saxonica.ee.stream.feed.ItemFeed
com.saxonica.ee.stream.watch.ForEachAction
com.saxonica.ee.stream.watch.ForEachGroupParallelAction
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.
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Field Summary
Fields inherited from class com.saxonica.ee.stream.watch.ForEachAction
actionPuller, bodyContext, watchManager
Fields inherited from class net.sf.saxon.event.Outputter
pipelineConfiguration, systemId
Fields inherited from interface javax.xml.transform.Result
PI_DISABLE_OUTPUT_ESCAPING, PI_ENABLE_OUTPUT_ESCAPING
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Constructor Summary
ConstructorsConstructorDescriptionForEachGroupParallelAction
(WatchManager watchManager, ForEachGroup expression, ItemFeed result, XPathContext context) -
Method Summary
Modifier and TypeMethodDescriptionvoid
Signal that an item (other than an element) that matches the selection has been found.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.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, getBodyContext, getInversion, getWatchManager, isActionConsuming, makeBodyContext, setInversion
Methods inherited from class com.saxonica.ee.stream.feed.ItemFeed
append, dynamicError, getContext, getExpression, getResultFeed, getTerminator, hasFailed, processItems, setExpression, setHasFailed, setTerminator
Methods inherited from class net.sf.saxon.event.ProxyOutputter
attribute, characters, comment, endDocument, endElement, getNextOutputter, namespace, open, processingInstruction, setUnparsedEntity, startContent, startDocument, startElement, startElement, usesTypeAnnotations
Methods inherited from class net.sf.saxon.event.Outputter
getConfiguration, getPipelineConfiguration, getStringReceiver, getSystemId, namespaces, setPipelineConfiguration, setSystemId, spreadStartElement
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Methods inherited from interface net.sf.saxon.event.Receiver
handlesAppend
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Constructor Details
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ForEachGroupParallelAction
public ForEachGroupParallelAction(WatchManager watchManager, ForEachGroup expression, ItemFeed result, XPathContext context)
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Method Details
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open
Description copied from class:ItemFeed
Start evaluating the expression. The default implementation does nothing.- Overrides:
open
in classForEachAction
- Parameters:
terminator
- used to achieve early exit- Throws:
XPathException
- if a dynamic error occurs
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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- Overrides:
startSelectedParentNode
in classForEachAction
- Parameters:
node
- the element or document node whose start event has been matchedlocationId
- 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 subsequent events, or null
- Throws:
XPathException
- if a dynamic error occurs while processing the start-element event
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append
Signal that an item (other than an element) that matches the selection has been found.- Specified by:
append
in interfaceReceiver
- Overrides:
append
in classForEachAction
- Parameters:
node
- the item that was matched.- Throws:
XPathException
- if the operation fails
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endSelectedParentNode
Signal that the endElement event has occurred for the element whose startElement event caused the Watch to be activated.- Overrides:
endSelectedParentNode
in classForEachAction
- 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 itXPathException
- May be raised if a constraint implemented by this Watch is violated
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close
Description copied from class:ItemFeed
Finish evaluating the expression.- Specified by:
close
in interfaceReceiver
- Overrides:
close
in classForEachAction
- Throws:
XPathException
- if a dynamic error occurs
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