- All Implemented Interfaces:
public final class MultithreadedContextMappingIterator extends java.lang.Object implements SequenceIteratorThis 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.
All Methods Instance Methods Concrete Methods Modifier and Type Method Description
close()Close the iterator.
discharge()Calling this method instructs the iterator to release any resources it holds, while still remaining able to deliver the remaining items in the sequence.
next()Get the next item in the sequence.
public MultithreadedContextMappingIterator(Expression action, XPathContextMinor context, int threads) throws XPathExceptionConstruct an Iterator that will apply a specified action expression to each Item returned by the current iterator of the supplied dynamic context.
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.
public Item next()Get the next item in the sequence. This method changes the state of the iterator.
- Specified by:
- 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.
public void close()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.
Closing an iterator is not necessary if the iterator is read to completion: if a call on
SequenceIterator.next()returns null, the iterator will be closed automatically. An explicit call on
SequenceIterator.close()is needed only when iteration is abandoned prematurely.
public void discharge()Calling this method instructs the iterator to release any resources it holds, while still remaining able to deliver the remaining items in the sequence. This may require the iterator to calculate the rest of the sequence eagerly. The method is called by a client if it anticipates that it might not read the iterator to completion, but it cannot guarantee that
SequenceIterator.close()will be called when no more items are needed.