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

- All Implemented Interfaces:
    `javax.xml.transform.Result`, `Receiver`

      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.

- - ### Field Summary

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

      `bodyContext`

    - ### 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`

  - ### Constructor Summary

    Constructors
    Constructor | Description
    --- | ---
    `ForEachGroupParallelAction​(WatchManager watchManager, ForEachGroup expression, ItemFeed result, XPathContext context)` |

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `void` | `append​(Item node)` | 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.
    `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, getBodyContext, getInversion, getWatchManager, isActionConsuming, makeBodyContext, setInversion`

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

      `append, dynamicError, getContext, getExpression, getResult, getTerminator, hasFailed, processItems, setExpression, setHasFailed, setTerminator`

    - ### Methods inherited from class net.sf.saxon.event.ProxyOutputter

      `attribute, characters, comment, endDocument, endElement, getNextOutputter, namespace, open, processingInstruction, setLocation, setUnparsedEntity, startContent, startDocument, startElement, startElement, usesTypeAnnotations`

    - ### Methods inherited from class net.sf.saxon.event.Outputter

      `getConfiguration, getPipelineConfiguration, getStringReceiver, getSystemId, namespaces, setPipelineConfiguration, setSystemId`

    - ### 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`

- - ### Constructor Detail

    - #### ForEachGroupParallelAction

          public ForEachGroupParallelAction​(WatchManager watchManager,
                                            ForEachGroup expression,
                                            ItemFeed 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.
      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
      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 that collects the contents of the selected node, or null
      Throws:
        `XPathException` - if a dynamic error occurs while processing the start-element event

    - #### append

          public void append​(Item node)
                      throws XPathException

      Signal that an item (other than an element) that matches the selection has been found.
      Specified by:
        `append` in interface `Receiver`
      Overrides:
        `append` in class `ForEachAction`
      Parameters:
        `node` - the item that was matched.
      Throws:
        `XPathException` - if the operation fails

    - #### 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.
      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.
      Specified by:
        `close` in interface `Receiver`
      Overrides:
        `close` in class `ForEachAction`
      Throws:
        `XPathException` - if a dynamic error occurs