Groups > comp.lang.java.programmer > #8317

Re: Bulk Array Element Allocation, is it faster?

From	Jan Burse <janburse@fastmail.fm>
Newsgroups	comp.lang.java.programmer
Subject	Re: Bulk Array Element Allocation, is it faster?
Date	2011-09-26 01:06 +0200
Organization	albasani.net
Message-ID	<j5oc5u$dpg$1@news.albasani.net> (permalink)
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Lew schrieb:
> You can't "optimize" allocation of n references
> to also create a block of n instances.  The optimizer
 > cannot know that that is the intended use of the array.

The following optimization works independent of
the use of the array. You can even nullify an
array element or set it to a newly created object.
So going from an unoptimized code:

     for (int i=0; i<n; i++) {
        lock heap
        bla[i] = new Bla(i);
        unlock heap
     }

To the following:


     lock heap
     p = allocate size n*X
     unlock heap
     for (int i=0; i<n; i++) {
        bla[i] = init p;
        p += x;
     }

Shouldn't be a problem for a decent compilers.
Various compilers do much more with loops. Why
do you doubt that this optimization is possible.

 > For the few cases where block allocation
 > *might* provide negligible speedup.

Oh, you don't really doubt that it is possible.
You rather doubt that it is worth. Well I
can tell you, in my application, the allocation
of small arrays with preallocated empty constructor
less initialized objects is done over and over.

I have recently run visual vm. It is really
what is mostly happening in the app during
the process of solving a problem.

And it seems that since it is so dominant any
changes in the way this is done are directly
seen in the timings. Here are the timings
again:

OS    JDK    Arch    Bulk    Lazy    Delta %
Win    1.7    64bit    8'159    8'975    10.0%
Win     1.6     64bit    8'771    9'805    11.8%
Win     1.6     32bit    14'587    14'744    1.1%
Win    1.5     32bit    17'139    17'405    1.6%
Mac    1.6    64bit    11'003    12'363    12.4%
Unix    1.6    32bit    26'517    26'858    1.3%

On 64bit the bulk is 10% faster for the
present application that makes heavy use
of allocating these objects and arrays.

 > As people keep pointing out in this conversation.

I know, it is logical that if it were that
the application would not make heavy use
of allocating these objects and arrays, then
nothing would be seen. But if nothing would
be seen at all, I wouldn't post here and
asking what is going on. But something is
seen, the 10%. It is not "nothing".

So what is going on in the 64bit?

Bye




Bye

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Thread

Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-25 03:17 +0200
  Re: Bulk Array Element Allocation, is it faster? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-09-24 21:37 -0400
    Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-25 10:39 +0200
  Re: Bulk Array Element Allocation, is it faster? Patricia Shanahan <pats@acm.org> - 2011-09-24 18:41 -0700
    Re: Bulk Array Element Allocation, is it faster? Robert Klemme <shortcutter@googlemail.com> - 2011-09-25 12:57 +0200
      Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-25 13:38 +0200
        Re: Bulk Array Element Allocation, is it faster? Robert Klemme <shortcutter@googlemail.com> - 2011-09-25 14:16 +0200
          Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-25 16:04 +0200
            Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-25 16:11 +0200
              Re: Bulk Array Element Allocation, is it faster? Patricia Shanahan <pats@acm.org> - 2011-09-25 09:30 -0700
            Re: Bulk Array Element Allocation, is it faster? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-09-25 10:59 -0400
              Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-25 17:14 +0200
                Re: Bulk Array Element Allocation, is it faster? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-09-25 15:26 +0000
                Re: Bulk Array Element Allocation, is it faster? Lew <lewbloch@gmail.com> - 2011-09-25 11:02 -0700
                Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-25 20:19 +0200
                Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-25 20:21 +0200
                Re: Bulk Array Element Allocation, is it faster? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-09-25 17:48 -0400
                Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-26 00:10 +0200
  Re: Bulk Array Element Allocation, is it faster? Roedy Green <see_website@mindprod.com.invalid> - 2011-09-24 19:05 -0700
    Re: Bulk Array Element Allocation, is it faster? Lew <lewbloch@gmail.com> - 2011-09-24 23:22 -0700
      Re: Bulk Array Element Allocation, is it faster? Roedy Green <see_website@mindprod.com.invalid> - 2011-09-25 00:23 -0700
        Re: Bulk Array Element Allocation, is it faster? Lew <lewbloch@gmail.com> - 2011-09-25 11:17 -0700
        Re: Bulk Array Element Allocation, is it faster? Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-09-25 14:00 -0500
    Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-25 10:47 +0200
      Re: Bulk Array Element Allocation, is it faster? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-09-25 08:07 -0400
        Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-25 19:21 +0200
          Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-25 19:41 +0200
          Re: Bulk Array Element Allocation, is it faster? Lew <lewbloch@gmail.com> - 2011-09-25 11:28 -0700
            Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-25 21:25 +0200
              Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-25 23:50 +0200
              Re: Bulk Array Element Allocation, is it faster? Lew <lewbloch@gmail.com> - 2011-09-25 15:43 -0700
                Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-26 01:06 +0200
                Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-26 01:21 +0200
                Re: Bulk Array Element Allocation, is it faster? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-09-26 06:00 +0000
                Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-26 14:52 +0200
                Re: Bulk Array Element Allocation, is it faster? Jan Burse <janburse@fastmail.fm> - 2011-09-26 15:02 +0200

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