[jira] [Comment Edited] (COLLECTIONS-722) IteratorUtils.chainedIterator() Performance Degrades

["Ng Tsz Sum (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/COLLECTIONS-722?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17530087#comment-17530087 ] 

Ng Tsz Sum edited comment on COLLECTIONS-722 at 4/29/22 4:22 PM:
-----------------------------------------------------------------

Possible solutions:

Since the problem is due to deeply nested IteratorChain triggering huge amount of *hasNext()* call,

1. In IteratorChain.java, add a method *currentIteratorHasNext* method to replace all call to *currentIterator.hasNext()* and this method will act as a cache to reduce call to {*}currentIterator.hasNext(){*}, of course we need to clear the cache whenever *currentIterator* next/remove is called or is pointing to something else. Drawback is the code are less readable.

2. Update the document in *IteratorUtils.chainedIterator(iterator1, iterator2)* to warn user not to use this method inside a for loop to chain IteratorChain. which will create deeply nested object and result in bad performance. Suggest them to use
*chainedIterator(final Iterator<? extends E>... iterators)*
or
*chainedIterator(final Collection<Iterator<? extends E>> iterators)*
instead.


was (Author: samabcde):
Possible solutions:

1. In IteratorChain.java, add a method *currentIteratorHasNext* method to replace all call to *currentIterator.next()* and this method will act as a cache to reduce call to {*}currentIterator.next(){*}, of course we need to clear the cache whenever *currentIterator* next/remove is called or is pointing to something else. Drawback is the code are less readable.

2. Update the document in *IteratorUtils.chainedIterator(iterator1, iterator2)* to warn user not to use this method inside a for loop to chain IteratorChain. which will create deeply nested object and result in bad performance. Suggest them to use
*chainedIterator(final Iterator<? extends E>... iterators)*
or
*chainedIterator(final Collection<Iterator<? extends E>> iterators)*
instead.

> IteratorUtils.chainedIterator() Performance Degrades
> ----------------------------------------------------
>
>                 Key: COLLECTIONS-722
>                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-722
>             Project: Commons Collections
>          Issue Type: Bug
>    Affects Versions: 4.1
>            Reporter: E P
>            Priority: Major
>         Attachments: IteratorUtilsTest.java
>
>
> IteratorUtils.chainedIterator() performance degrades when chaining iterators with chained iterators.   The slowdown appears to be exponential, based upon the number of chains created.  The attached test shows the issue.  
> As a reference, the same test below works as expected using Google's Guava Iterator.concat() functionality.   It is possible I am misusing the API, but the javadoc did not indicate as much.
>  



--
This message was sent by Atlassian Jira
(v8.20.7#820007)