Groups > comp.lang.java.programmer > #5742

Re: Why "lock" functionality is introduced for all the objects?

From	Lew <noone@lewscanon.com>
Newsgroups	comp.lang.java.programmer
Subject	Re: Why "lock" functionality is introduced for all the objects?
Date	2011-06-28 14:33 -0400
Organization	albasani.net
Message-ID	<iud6p5$q6s$1@news.albasani.net> (permalink)
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On 06/28/2011 02:23 PM, 
supercalifragilisticexpialadiamaticonormalizeringelimatisticantations wrote:
> On 28/06/2011 2:13 PM, Lew wrote:
>> Michal Kleczek wrote:
>>> Lew wrote:
>>>> Show me the numbers. What penalty?
>>>
>>> It is (almost) twice as much memory as it could be and twice as much GC
>>> cycles. Almost because in real world the number of objects that you
>>> need to
>>
>> Nonsense. It's an extra 4 bytes per object. Most objects are much larger
>> than 4 bytes,
>
> Bullpuckey, other than that a nontrivial object is always at least 12 bytes

So 4 bytes overhead is less than 100%, as I said.

> due to Java's bloated object headers plus alignment. Ignoring that, it's quite
> common to have lots of small objects at runtime -- from boxed primitives (4
> bytes for most and 8 bytes for Longs and Doubles, plus object headers) to
> short strings (two bytes per character plus four for the length field = 8 for
> a two-letter word and 4 for an empty string -- again, plus object headers) and

Most strings in a typical program are non-empty and generally longer than two 
bytes.  A good percentage are interned.  Strings in many runtime contexts 
refer to substrings of those already in memory, saving overhead.

Integer objects make up a small fraction of most programs.  Many Integer 
instances are shared, especially if one follows best practices.  Not a lot of 
memory pressure there.

Double and Long, even fewer.

> the occasional content-free pure-behavior object (abstract factories, strategy
> pattern implementations, event listeners, plus most of the things you'd use an
> anonymous inner class for ...). Small collections are a bit larger but an 8
> byte object header is still likely to be a fair percentage; and their

What percentage is "fair"?  Surely less than 100%, as I claim.
\
> iterators may contain as little as a single integer index plus a single
> pointer (ArrayList's likely does) and so be the same size as a Long or a Double.
>
> And then there's all the objects with one or two reference type fields. Four
> bytes each, on a 32-bit JVM. You can't count the "nested" objects' own sizes,
> because they each have their own object header.
>
> Objects with many fields are quite a bit rarer than ones with only one or two
> fields. *Classes* with many fields are less common, and usually there will be
> fewer live instances at runtime.
>
> Ultimately, overhead fraction = average bytes directly in fields (at most 4
> for most fields on 32-bit systems, excepting long and double primitive fields)
> divided by header size, where the average is over a *typical population of
> live objects in a running system* rather than over a set of, say, classes in
> use in a system.

You show only that the overhead of 4 bytes per object is less than 100% of the 
object's memory footprint, which is what I said.

Which footprint can be reduced by HotSpot, to the point of pulling an object 
out of the heap altogether.

Where are the numbers?  Everyone's arguing from speculation.  Show me the numbers.

Real numbers.  From actual runs.  What is the overhead, really?  Stop making 
shit up.

Show me the numbers.

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

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Why "lock" functionality is introduced for all the objects? Alex J <vstrength@gmail.com> - 2011-06-28 02:29 -0700
  Re: Why "lock" functionality is introduced for all the objects? Lew <noone@lewscanon.com> - 2011-06-28 07:33 -0400
    OT "sic" (was Re: Why "lock" functionality is introduced for all the objects? blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-06-28 15:56 +0000
      Re: OT "sic" (was Re: Why "lock" functionality is introduced for all the objects? Lew <noone@lewscanon.com> - 2011-06-28 12:19 -0400
    Re: Why "lock" functionality is introduced for all the objects? Michal Kleczek <kleku75@gmail.com> - 2011-06-28 18:41 +0200
      Re: Why "lock" functionality is introduced for all the objects? Lew <noone@lewscanon.com> - 2011-06-28 13:10 -0400
        Re: Why "lock" functionality is introduced for all the objects? Michal Kleczek <kleku75@gmail.com> - 2011-06-28 19:53 +0200
          Re: Why "lock" functionality is introduced for all the objects? Lew <noone@lewscanon.com> - 2011-06-28 14:13 -0400
            Re: Why "lock" functionality is introduced for all the objects? supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-06-28 14:23 -0400
              Re: Why "lock" functionality is introduced for all the objects? Lew <noone@lewscanon.com> - 2011-06-28 14:33 -0400
                Re: Why "lock" functionality is introduced for all the objects? supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-06-28 14:52 -0400
                Re: Why "lock" functionality is introduced for all the objects? Lew <noone@lewscanon.com> - 2011-06-28 16:20 -0400
                Re: Why "lock" functionality is introduced for all the objects? supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-06-29 00:53 -0400
                Re: Why "lock" functionality is introduced for all the objects? Lew <noone@lewscanon.com> - 2011-06-29 01:04 -0400
                Re: Why "lock" functionality is introduced for all the objects? supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-06-29 01:43 -0400
              Re: Why "lock" functionality is introduced for all the objects? Patricia Shanahan <pats@acm.org> - 2011-06-28 11:42 -0700
                Re: Why "lock" functionality is introduced for all the objects? supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-06-28 14:54 -0400
                Re: Why "lock" functionality is introduced for all the objects? Patricia Shanahan <pats@acm.org> - 2011-06-28 12:34 -0700
                Re: Why "lock" functionality is introduced for all the objects? markspace <-@.> - 2011-06-28 13:20 -0700
                Re: Why "lock" functionality is introduced for all the objects? Patricia Shanahan <pats@acm.org> - 2011-06-28 13:44 -0700
                Re: Why "lock" functionality is introduced for all the objects? supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-06-29 01:05 -0400
                Re: Why "lock" functionality is introduced for all the objects? Lew <noone@lewscanon.com> - 2011-06-28 16:21 -0400
                Re: Why "lock" functionality is introduced for all the objects? supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-06-29 01:06 -0400
                Re: Why "lock" functionality is introduced for all the objects? BGB <cr88192@hotmail.com> - 2011-06-28 14:30 -0700
          Re: Why "lock" functionality is introduced for all the objects? Robert Klemme <shortcutter@googlemail.com> - 2011-06-29 18:56 +0200
      Re: Why "lock" functionality is introduced for all the objects? BGB <cr88192@hotmail.com> - 2011-06-28 13:43 -0700
        Re: Why "lock" functionality is introduced for all the objects? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-06-28 20:43 -0400
          Re: Why "lock" functionality is introduced for all the objects? BGB <cr88192@hotmail.com> - 2011-06-28 21:14 -0700
        Re: Why "lock" functionality is introduced for all the objects? supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-06-29 01:12 -0400
          Re: Why "lock" functionality is introduced for all the objects? Joshua Maurice <joshuamaurice@gmail.com> - 2011-07-01 18:28 -0700
            Re: Why "lock" functionality is introduced for all the objects? supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-07-02 00:19 -0400
          Re: Why "lock" functionality is introduced for all the objects? Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-07-01 19:05 -0700
            Re: Why "lock" functionality is introduced for all the objects? supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-07-02 00:26 -0400
            Re: Why "lock" functionality is introduced for all the objects? BGB <cr88192@hotmail.com> - 2011-07-04 09:39 -0700
              Re: Why "lock" functionality is introduced for all the objects? supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-07-05 02:11 -0400
    Re: Why "lock" functionality is introduced for all the objects? Alex J <vstrength@gmail.com> - 2011-07-05 16:56 -0700
      Re: Why "lock" functionality is introduced for all the objects? "John B. Matthews" <nospam@nospam.invalid> - 2011-07-06 00:57 -0400
      Re: Why "lock" functionality is introduced for all the objects? supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-07-06 05:55 -0400
  Re: Why "lock" functionality is introduced for all the objects? Lew <noone@lewscanon.com> - 2011-06-28 14:40 -0400
  Re: Why "lock" functionality is introduced for all the objects? Robert Klemme <shortcutter@googlemail.com> - 2011-06-29 19:15 +0200
  Re: Why "lock" functionality is introduced for all the objects? Tom Anderson <twic@urchin.earth.li> - 2011-06-30 23:04 +0100
    Re: Why "lock" functionality is introduced for all the objects? KitKat <kitkat_11697@gmail.example.com> - 2011-06-30 18:29 -0400
      Re: Why "lock" functionality is introduced for all the objects? Patricia Shanahan <pats@acm.org> - 2011-06-30 17:05 -0700
        Re: Why "lock" functionality is introduced for all the objects? KitKat <kitkat_11697@gmail.example.com> - 2011-06-30 20:17 -0400
          Re: Why "lock" functionality is introduced for all the objects? Tom Anderson <twic@urchin.earth.li> - 2011-07-01 21:22 +0100
      Re: Why "lock" functionality is introduced for all the objects? Tom Anderson <twic@urchin.earth.li> - 2011-07-01 21:40 +0100
        Re: Why "lock" functionality is introduced for all the objects? KitKat <kitkat_11697@gmail.example.com> - 2011-07-01 18:08 -0400
          Re: Why "lock" functionality is introduced for all the objects? BGB <cr88192@hotmail.com> - 2011-07-05 12:15 -0700
            Re: Why "lock" functionality is introduced for all the objects? KitKat <kitkat_11697@gmail.example.com> - 2011-07-05 15:30 -0400
              Re: Why "lock" functionality is introduced for all the objects? blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-07-05 21:10 +0000
                Re: Why "lock" functionality is introduced for all the objects? BGB <cr88192@hotmail.com> - 2011-07-05 22:08 -0700
                Re: Why "lock" functionality is introduced for all the objects? KitKat <kitkat_11697@gmail.example.com> - 2011-07-06 05:57 -0400
                Re: Why "lock" functionality is introduced for all the objects? blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-07-06 17:07 +0000
                Re: Why "lock" functionality is introduced for all the objects? Steve Erwin <trollHunter@Usenet.4.usenetizens.org.invalid> - 2011-07-07 04:08 +1000
                Re: Why "lock" functionality is introduced for all the objects? blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-07-06 19:09 +0000
                Re: Why "lock" functionality is introduced for all the objects? Steve Erwin <trollHunter@Usenet.4.usenetizens.org.invalid> - 2011-07-07 09:26 +1000
                Re: Why "lock" functionality is introduced for all the objects? KitKat <kitkat_11697@gmail.example.com> - 2011-07-06 20:25 -0400
                Re: Why "lock" functionality is introduced for all the objects? blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-07-07 19:37 +0000
                Re: Why "lock" functionality is introduced for all the objects? blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-07-07 19:35 +0000
                Re: Why "lock" functionality is introduced for all the objects? Steve Erwin <trollHunter@Usenet.4.usenetizens.org.invalid> - 2011-07-07 14:34 -0700
                OT names/nyms/etc. (was Re: Why "lock" functionality is introduced for all the objects?) blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-07-08 17:19 +0000
                Re: OT names/nyms/etc. (was Re: Why "lock" functionality is introduced for all the objects?) Steve Erwin <trollHunter@Usenet.4.usenetizens.org.invalid> - 2011-07-09 05:41 +1000
                Re: OT names/nyms/etc. (was Re: Why "lock" functionality is introduced for all the objects?) blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-07-08 19:58 +0000
                Re: OT names/nyms/etc. (was Re: Why "lock" functionality is introduced for all the objects?) lewbloch <lewbloch@gmail.com> - 2011-07-08 13:45 -0700
                Re: OT names/nyms/etc. (was Re: Why "lock" functionality is introduced for all the objects?) Steve Erwin <trollHunter@Usenet.4.usenetizens.org.invalid> - 2011-07-10 01:50 -0400
                Re: OT names/nyms/etc. (was Re: Why "lock" functionality is introduced for all the objects?) blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-07-10 19:15 +0000
                Re: OT names/nyms/etc. (was Re: Why "lock" functionality is introduced for all the objects?) KitKat <kitkat_11697@gmail.example.com> - 2011-07-10 18:38 -0400
                Re: OT names/nyms/etc. (was Re: Why "lock" functionality is introduced for all the objects?) KitKat <kitkat_11697@gmail.example.com> - 2011-07-09 00:29 -0400
                Re: Why "lock" functionality is introduced for all the objects? KitKat <kitkat_11697@gmail.example.com> - 2011-07-09 00:26 -0400
                Re: Why "lock" functionality is introduced for all the objects? KitKat <kitkat_11697@gmail.example.com> - 2011-07-06 20:05 -0400
                Re: Why "lock" functionality is introduced for all the objects? Steve Erwin <trollHunter@Usenet.4.usenetizens.org.invalid> - 2011-07-07 10:24 +1000
                Re: Why "lock" functionality is introduced for all the objects? KitKat <kitkat_11697@gmail.example.com> - 2011-07-06 21:52 -0400
                Re: Why "lock" functionality is introduced for all the objects? Steve Erwin <trollHunter@Usenet.4.usenetizens.org.invalid> - 2011-07-07 12:43 +1000
                Re: Why "lock" functionality is introduced for all the objects? KitKat <kitkat_11697@gmail.example.com> - 2011-07-06 23:00 -0400

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