Class 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.
    • Method Detail

      • open

        public void open​(Terminator terminator)
                  throws XPathException
        Description copied from class: ItemFeed
        Start evaluating the expression. The default implementation does nothing.
        open in class ForEachAction
        terminator - used to achieve early exit
        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
        startSelectedParentNode in class ForEachAction
        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)
        a Receiver to be notified of subsequent events, or null
        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
        append in class ForEachAction
        node - the item that was matched.
        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.
        endSelectedParentNode in class ForEachAction
        locationId - the location of the node in the source, or of the instruction that created it
        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