Package com.saxonica.ee.optim

Class MultithreadedContextMappingIterator

  • All Implemented Interfaces:
    java.io.Closeable, java.lang.AutoCloseable, SequenceIterator
    public final class MultithreadedContextMappingIterator
extends java.lang.Object
implements SequenceIterator
    This class performs the same role as ContextMappingIterator, but using multiple threads.

    It merges a sequence of sequences into a single flat sequence. It takes as inputs an iteration, and an "action" expression to be applied to each Item returned by that iteration, with that item as the context item. The action expression itself returns another iterator. The result is an iteration of the concatenation of all the iterations returned by the action expression.

    • Constructor Detail

      • MultithreadedContextMappingIterator

        public MultithreadedContextMappingIterator​(Expression action,
                                           XPathContextMinor context,
                                           int threads)
                                    throws XPathException
        Construct an Iterator that will apply a specified action expression to each Item returned by the current iterator of the supplied dynamic context.
        Parameters:
        action - the mapping expression to be applied
        context - the processing context. The action expression is applied to each item returned by context.getCurrentIterator() in turn.
        threads - the number of threads to be used (in addition to the base evaluation thread) These threads are used to evaluate the action expression. The current thread is used to evaluate the base iterator and to gather the results of invoking the action expressions in the right order.
        Throws:
        XPathException

    • Method Detail

      • next

        public Item next()
          throws XPathException
        Description copied from interface: SequenceIterator
        Get the next item in the sequence. This method changes the state of the iterator.
        Specified by:
        next in interface SequenceIterator
        Returns:
        the next item, or null if there are no more items. Once a call on next() has returned null, no further calls should be made. The preferred action for an iterator if subsequent calls on next() are made is to return null again, and all implementations within Saxon follow this rule.
        Throws:
        XPathException - if an error occurs retrieving the next item

      • close

        public void close()
        Description copied from interface: SequenceIterator
        Close the iterator. This indicates to the supplier of the data that the client does not require any more items to be delivered by the iterator. This may enable the supplier to release resources. After calling close(), no further calls on the iterator should be made; if further calls are made, the effect of such calls is undefined.

        For example, the iterator returned by the unparsed-text-lines() function has a close() method that causes the underlying input stream to be closed, whether or not the file has been read to completion.

        Closing an iterator is important when the data is being "pushed" in another thread. Closing the iterator terminates that thread and means that it needs to do no additional work. Indeed, failing to close the iterator may cause the push thread to hang waiting for the buffer to be emptied.

        Specified by:
        close in interface java.lang.AutoCloseable
        Specified by:
        close in interface java.io.Closeable
        Specified by:
        close in interface SequenceIterator