Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!news.albasani.net!.POSTED!not-for-mail
From: Jan Burse <janburse@fastmail.fm>
Newsgroups: comp.lang.java.programmer
Subject: Re: Bulk Array Element Allocation, is it faster?
Date: Sun, 25 Sep 2011 10:47:02 +0200
Organization: albasani.net
Lines: 34
Message-ID: <j5mpq6$lra$1@news.albasani.net>
References: <j5lvf0$bhl$1@news.albasani.net> <ke2t77p38ktjf6bi8fvng7mo0a2a0cad8e@4ax.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-Trace: news.albasani.net ZP5kxbc07/stwOykOslLqmYlm4cMI/HOwxS8KQzyPXeDnzCeI2PgZ1P/Sh1blR28sbVGmLiW4cT4u76ycWpHispeUK6WjyplqGPUeJz9X7fb7IebqYfdRtNHBX+dRVR2
NNTP-Posting-Date: Sun, 25 Sep 2011 08:47:02 +0000 (UTC)
Injection-Info: news.albasani.net; logging-data="hjzYNkkQYh/aT1QSGzLHBPutVKxKuZgPXJuRxhvVTKk5wlfTqwJfIgWwYWr04qW6J2d29auKBNzbiTNzUuBUdU/+Pet5dAHKO26jSQAcqLKJ9UVVLLAaemQIDvabSFyj"; mail-complaints-to="abuse@albasani.net"
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:6.0.2) Gecko/20110902 Firefox/6.0.2 SeaMonkey/2.3.3
In-Reply-To: <ke2t77p38ktjf6bi8fvng7mo0a2a0cad8e@4ax.com>
Cancel-Lock: sha1:Ow+i4Nde2xat8L1sleZkONO5aYU=
Xref: x330-a1.tempe.blueboxinc.net comp.lang.java.programmer:8284

Roedy Green schrieb:
> new does two things:
> 1. allocates X bytes of space
> 2. initialises that block of space to a pattern.

So a dumb translation of the loop would be:

   1. for each i between 0 and n-1
        1.1 allocates X bytes of space
        1.2 call the initializer

Then I was more thinking that the loop does the
following, i.e. is cleverly compiled to:

   1. allocates n*X bytes of space
   2. for each i between 0 and n-1
        2.1 call the initializer for location X*i

At least I would hand assembler it like this.
Saving n-1 calls to the heap allocator.

But maybe positive effect is not based on such
a clever allocation and only on what Patricia said.

I was already googling a little bit about the
compilation techniques found for JIT today, but
did not yet hit any evidence for clever loop
allocation, but it is so obvious I really it
must be done. But maybe it is not done because
of multi-threading or GC, who knows...

Bye