[infinispan-dev] Avoid Collections.emptySet() / emptyMap() / emptyList

[Galder Zamarreño]

On Oct 19, 2012, at 7:20 PM, David M. Lloyd <david.lloyd at redhat.com> wrote:

> Also be aware that JBMAR has specific optimizations for the JDK empty 
> collections - they are represented by a single byte in the stream.

Well, it's actually 3 bytes that you use to represent empty collections (at least in 1.3.15ga):

write(ID_NEW_OBJECT);
write(ID_CLASS_CLASS);
write(classByte);

Whereas with our externalizers, these get resolved via object writer (which gets called before your code to detect empty collections) and it only writes 1 byte:

write(externalizerId);

Cheers,

> 
> On 10/19/2012 11:28 AM, Dan Berindei wrote:
>> Galder, what JDK are you using? OpenJDK 1.7 uses
>> EmptyIterator.EMPTY_ITERATOR since 2007:
>> 
>> http://hg.openjdk.java.net/jdk7/jdk7/jdk/annotate/37a05a11f281/src/share/classes/java/util/Collections.java
>> 
>> I don't have JDK 1.6 sources on hand to check, but I don't think it's
>> worth optimizing for such an old version anyway.
>> 
>> Cheers
>> Dan
>> 
>> 
>> On Fri, Oct 19, 2012 at 5:50 PM, Vladimir Blagojevic
>> <vblagoje at redhat.com <mailto:vblagoje at redhat.com>> wrote:
>> 
>>    Cool! Did not know about this! Is this original idea or others are
>>    already doing this?
>>    On 12-10-19 8:31 AM, Galder Zamarreño wrote:
>>> Hi all,
>>> 
>>> Re:
>>    https://github.com/galderz/infinispan/commit/0609207d13216de81d77ff51dc20652ce270c635
>>> 
>>> Please avoid using these JDK methods where possible. I've created
>>    alternative versions in InfinispanCollections util class that
>>    provide a better implementation.
>>> 
>>> The problem with the JDK versions is that even if these
>>    collections are immutable, if you wanna iterate them (i.e. for(X :
>>    emptySet) ), they'll create a brand new Iterator every time they're
>>    looped, and that generates useless garbage.
>>> 
>>> The InfinispanCollections versions of emptyX will return a
>>    constant singleton iterator which avoids this problem, and avoids
>>    the need for client code to check if the collection is empty before
>>    looping.
>>> 
>>> Cheers,
>>> --
>>> Galder Zamarreño
>>> galder at redhat.com <mailto:galder at redhat.com>
>>> twitter.com/galderz <http://twitter.com/galderz>
>>> 
>>> Project Lead, Escalante
>>> http://escalante.io
>>> 
>>> Engineer, Infinispan
>>> http://infinispan.org
>>> 
>>> 
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> 
> 
> -- 
> - DML
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--
Galder Zamarreño
galder at redhat.com
twitter.com/galderz

Project Lead, Escalante
http://escalante.io

Engineer, Infinispan
http://infinispan.org