You are viewing a plain text version of this content. The canonical link for it is here.
Posted to issues@commons.apache.org by "Adrian Nistor (JIRA)" <ji...@apache.org> on 2012/07/25 00:05:33 UTC
[jira] [Created] (COLLECTIONS-426) performance problem in
ListOrderedSet.retainAll()
Adrian Nistor created COLLECTIONS-426:
-----------------------------------------
Summary: performance problem in ListOrderedSet.retainAll()
Key: COLLECTIONS-426
URL: https://issues.apache.org/jira/browse/COLLECTIONS-426
Project: Commons Collections
Issue Type: Bug
Affects Versions: 3.2.1
Environment: java 1.6.0_24
Ubuntu 11.10
Reporter: Adrian Nistor
Attachments: Test.java, patch.diff
Hi,
I am encountering a performance problem in ListOrderedSet.retainAll().
It appears in version 3.2.1 and also in revision 1365132. I attached
a test that exposes this problem and a patch that fixes it. On my
machine, for this test, the patch provides a 263X speedup.
To run the test, just do:
$ java Test
The output for the un-patched version is:
Time is 3682
The output for the patched version is:
Time is 14
The problem is that the code for method
"ListOrderedSet.retainAll(Collection<?> coll)" is:
{code:java|borderStyle=solid}
public boolean retainAll(Collection<?> coll) {
boolean result = collection.retainAll(coll);
....
}
{code}
because "collection.retainAll(coll)" has quadratic complexity if
parameter "coll" is a List. Conceptually, the solution is to call
"coll.retainAll(collection)" which has linear complexity (not
quadratic), because "collection" is always a HashSet (we know this,
because "collection" is an inherited field of ListOrderedSet, and thus
cannot have another type). See the
"java.util.AbstractCollection.retainAll()" code inlined below for why
one call has quadratic complexity, and the other has linear
complexity.
Directly calling "coll.retainAll(collection)" would change the
behavior of ListOrderedSet.retainAll(), which is why the patch seems a
bit involved. In reality, the patch simulates the behavior of
"coll.retainAll(collection)" (which is just the intersection of two
collections). You can easily see this by looking at the patch and at
the "java.util.AbstractCollection.retainAll()" code inlined below.
"collection.retainAll(coll)" is "java.util.HashSet.retainAll()", which
is "java.util.AbstractCollection.retainAll()", which has the code:
{code:java|borderStyle=solid}
public boolean retainAll(Collection<?> c) {
boolean modified = false;
Iterator<E> e = iterator();
while (e.hasNext()) {
if (!c.contains(e.next())) {
e.remove();
modified = true;
}
}
return modified;
}
{code}
Is this a bug, or am I misunderstanding the intended behavior? If so,
can you please confirm if the patch is correct?
Thanks,
Adrian
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira
[jira] [Updated] (COLLECTIONS-426) performance problem in
ListOrderedSet.retainAll()
Posted by "Adrian Nistor (JIRA)" <ji...@apache.org>.
[ https://issues.apache.org/jira/browse/COLLECTIONS-426?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Adrian Nistor updated COLLECTIONS-426:
--------------------------------------
Attachment: Test.java
patch.diff
> performance problem in ListOrderedSet.retainAll()
> -------------------------------------------------
>
> Key: COLLECTIONS-426
> URL: https://issues.apache.org/jira/browse/COLLECTIONS-426
> Project: Commons Collections
> Issue Type: Bug
> Affects Versions: 3.2.1
> Environment: java 1.6.0_24
> Ubuntu 11.10
> Reporter: Adrian Nistor
> Attachments: Test.java, patch.diff
>
>
> Hi,
> I am encountering a performance problem in ListOrderedSet.retainAll().
> It appears in version 3.2.1 and also in revision 1365132. I attached
> a test that exposes this problem and a patch that fixes it. On my
> machine, for this test, the patch provides a 263X speedup.
> To run the test, just do:
> $ java Test
> The output for the un-patched version is:
> Time is 3682
> The output for the patched version is:
> Time is 14
> The problem is that the code for method
> "ListOrderedSet.retainAll(Collection<?> coll)" is:
> {code:java|borderStyle=solid}
> public boolean retainAll(Collection<?> coll) {
> boolean result = collection.retainAll(coll);
> ....
> }
> {code}
> because "collection.retainAll(coll)" has quadratic complexity if
> parameter "coll" is a List. Conceptually, the solution is to call
> "coll.retainAll(collection)" which has linear complexity (not
> quadratic), because "collection" is always a HashSet (we know this,
> because "collection" is an inherited field of ListOrderedSet, and thus
> cannot have another type). See the
> "java.util.AbstractCollection.retainAll()" code inlined below for why
> one call has quadratic complexity, and the other has linear
> complexity.
> Directly calling "coll.retainAll(collection)" would change the
> behavior of ListOrderedSet.retainAll(), which is why the patch seems a
> bit involved. In reality, the patch simulates the behavior of
> "coll.retainAll(collection)" (which is just the intersection of two
> collections). You can easily see this by looking at the patch and at
> the "java.util.AbstractCollection.retainAll()" code inlined below.
> "collection.retainAll(coll)" is "java.util.HashSet.retainAll()", which
> is "java.util.AbstractCollection.retainAll()", which has the code:
> {code:java|borderStyle=solid}
> public boolean retainAll(Collection<?> c) {
> boolean modified = false;
> Iterator<E> e = iterator();
> while (e.hasNext()) {
> if (!c.contains(e.next())) {
> e.remove();
> modified = true;
> }
> }
> return modified;
> }
> {code}
> Is this a bug, or am I misunderstanding the intended behavior? If so,
> can you please confirm if the patch is correct?
> Thanks,
> Adrian
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira