Package com.saxonica.ee.parallel

Class MultithreadedItemMappingIterator

java.lang.Object

net.sf.saxon.expr.ItemMappingIterator

com.saxonica.ee.parallel.MultithreadedItemMappingIterator

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable, LastPositionFinder, SequenceIterator, LookaheadIterator

public class MultithreadedItemMappingIterator
extends ItemMappingIterator

Parallel-processing version of the ItemMappingIterator class, which executes a mapping function for each item in a sequence. In this implementation (which is designed initially for use by the collection() function), the order of items in the result sequence retains the order of items in the input sequence.

Constructor Summary

Constructors

Constructor	Description
MultithreadedItemMappingIterator(SequenceIterator base, ItemMappingFunction action, MultithreadingFactory factory)

Method Summary

Modifier and Type	Method	Description
void	close()	The user of a SequenceIterator is encouraged to call the close() method if no further items are required from the sequence of items delivered by the SequenceIterator.
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.
protected int	getMaxThreads()	Overridable method that decides how many threads to use.
Item	next()	Get the next item in the sequence.

Methods inherited from class net.sf.saxon.expr.ItemMappingIterator

filter, getBaseIterator, getLength, getMappingFunction, hasNext, isOneToOne, map, setOneToOne, supportsGetLength, supportsHasNext

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

MultithreadedItemMappingIterator

public MultithreadedItemMappingIterator(SequenceIterator base,
                                        ItemMappingFunction action,
                                        MultithreadingFactory factory)
                                 throws XPathException

Throws:

XPathException

Method Detail

getMaxThreads

protected int getMaxThreads()

Overridable method that decides how many threads to use. The default implementation returns the value of Runtime.getRuntime().availableProcessors(), or 1 if greater.

Returns:

the maximum number of threads to use.

next

public Item next()

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

Overrides:

next in class ItemMappingIterator

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.

close

public void close()

The user of a SequenceIterator is encouraged to call the close() method if no further items are required from the sequence of items delivered by the SequenceIterator. This allows resources to be released. A SequenceIterator is NOT normally closed explicitly if it has been read to completion. This implementation of the close() method shuts down the ExecutorService used to schedule threads.

Specified by:

close in interface java.lang.AutoCloseable

Specified by:

close in interface java.io.Closeable

Specified by:

close in interface SequenceIterator

Overrides:

close in class ItemMappingIterator

discharge

public void discharge()

Description copied from interface: SequenceIterator

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.

Specified by:

discharge in interface SequenceIterator

Overrides:

discharge in class ItemMappingIterator