Re: Safety Of Non-Synchronized Collections

Newsgroups	comp.lang.java.help
Date	2013-01-03 15:30 -0800
References	<kbvhvc$le1$1@dont-email.me> <g23be8tkcm1sh99m4030ggvr9vesj6fj4r@4ax.com>
Message-ID	<e1ce2d29-dca1-4364-8cd3-5512dd0694c5@googlegroups.com> (permalink)
Subject	Re: Safety Of Non-Synchronized Collections
From	Lew <lewbloch@gmail.com>

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Roedy Green wrote:
>Steve wrote, quoted or indirectly quoted someone who said :
>>The bottom line seemed to be that the two collections were the same 
>>thing except that a StringBuffer is synchronized, is a thread safe and 
>>does a little less well in performance as compared to StringBuilder 
>>which are not those things.
> 
> Your rules of thumb will work most of the time.  Someone might think
> of a pathological case, but I can't offhand. 

Well, there's the fact that StringBuffer is not thread-safe.

> I always use StringBuilder in preference to StringBuffer except when I
> am writing for very old versions of Java (as in Wassup).  I am also

Good policy.

> forced to use it in Regex search/replace which uses the legacy
> StringBuffer class.
> 
> But actually I nearly always use FastCat which is much more memory
> efficient than StringBuilder.  You have to estimate how many pieces
> you will join, not their total length. That is much easier.
> 
> see http://mindprod.com/products.html#FASTCAT
> 
> You almost never share a StringBuilder between threads. It is
> invariably referenced by a local variable. So the need for thread safe
> code rarely comes up.
> 
> I wish there were an optimisation possible in such code. It composes a
> char array which it then converts to a String. In theory it should be
> possible to create the String from that array which is no longer
> needed without making a copy.  The problem is making sure there are no
> references to the array.  You build a proto string containing a char
> array, copy strings into in, then convert it into a real string. Such
> code could prevent an references to the array from being created.

How necessary is this optimization? How much does it hurt performance? 
How much is that affected by HotSpot?

-- 
Lew

Thread

Safety Of Non-Synchronized Collections Steve <tinker123@gmail.com> - 2013-01-01 15:46 -0500
  Re: Safety Of Non-Synchronized Collections Knute Johnson <nospam@knutejohnson.com> - 2013-01-01 14:18 -0800
    Re: Safety Of Non-Synchronized Collections Lew <lewbloch@gmail.com> - 2013-01-01 15:43 -0800
  Re: Safety Of Non-Synchronized Collections markspace <markspace@nospam.nospam> - 2013-01-01 16:17 -0800
    Re: Safety Of Non-Synchronized Collections Lew <lewbloch@gmail.com> - 2013-01-02 11:12 -0800
      Re: Safety Of Non-Synchronized Collections markspace <markspace@nospam.nospam> - 2013-01-02 12:56 -0800
        Re: Safety Of Non-Synchronized Collections Lew <lewbloch@gmail.com> - 2013-01-02 17:46 -0800
  Re: Safety Of Non-Synchronized Collections Roedy Green <see_website@mindprod.com.invalid> - 2013-01-03 05:59 -0800
    Re: Safety Of Non-Synchronized Collections Lew <lewbloch@gmail.com> - 2013-01-03 15:30 -0800
      Re: Safety Of Non-Synchronized Collections Roedy Green <see_website@mindprod.com.invalid> - 2013-01-09 12:17 -0800
        Re: Safety Of Non-Synchronized Collections Lew <lewbloch@gmail.com> - 2013-01-09 12:56 -0800
          Re: Safety Of Non-Synchronized Collections Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-01-09 13:10 -0800
            Re: Safety Of Non-Synchronized Collections Lew <lewbloch@gmail.com> - 2013-01-09 14:51 -0800
              Re: Safety Of Non-Synchronized Collections Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-01-09 15:22 -0800
                Re: Safety Of Non-Synchronized Collections Lew <lewbloch@gmail.com> - 2013-01-09 16:26 -0800
                Re: Safety Of Non-Synchronized Collections Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-01-09 16:42 -0800
                Re: Safety Of Non-Synchronized Collections Lew <lewbloch@gmail.com> - 2013-01-09 16:54 -0800
                Re: Safety Of Non-Synchronized Collections Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-01-10 10:30 -0800
                Re: Safety Of Non-Synchronized Collections Lew <lewbloch@gmail.com> - 2013-01-10 10:58 -0800
                Re: Safety Of Non-Synchronized Collections markspace <markspace@nospam.nospam> - 2013-01-09 16:50 -0800
                Re: Safety Of Non-Synchronized Collections Lew <lewbloch@gmail.com> - 2013-01-09 16:59 -0800
                Re: Safety Of Non-Synchronized Collections markspace <markspace@nospam.nospam> - 2013-01-10 08:18 -0800
                Re: Safety Of Non-Synchronized Collections Lew <lewbloch@gmail.com> - 2013-01-10 10:49 -0800
                Re: Safety Of Non-Synchronized Collections Jukka Lahtinen <jtfjdehf@hotmail.com.invalid> - 2013-01-10 13:37 +0200
                Re: Safety Of Non-Synchronized Collections Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-01-10 09:27 -0500
                Re: Safety Of Non-Synchronized Collections Jukka Lahtinen <jtfjdehf@hotmail.com.invalid> - 2013-01-10 17:14 +0200
                Re: Safety Of Non-Synchronized Collections Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-01-10 11:44 -0500
                Re: Safety Of Non-Synchronized Collections Jukka Lahtinen <jtfjdehf@hotmail.com.invalid> - 2013-01-10 23:41 +0200
                Re: Safety Of Non-Synchronized Collections Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-01-10 17:14 -0500
                Re: Safety Of Non-Synchronized Collections Jukka Lahtinen <jtfjdehf@hotmail.com.invalid> - 2013-01-11 09:10 +0200
                Re: Safety Of Non-Synchronized Collections Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-01-11 08:25 -0500

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