Mailing-List: contact users-help@tomcat.apache.org; run by ezmlm
Precedence: bulk
Reply-To: "Tomcat Users List" <users@tomcat.apache.org>
Received-SPF: pass (athena.apache.org: domain of rosenberg.leon@googlemail.com
 designates 74.125.44.153 as permitted sender)
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=googlemail.com; s=gamma;
        h=message-id:date:from:to:subject:in-reply-to:mime-version
         :content-type:content-transfer-encoding:content-disposition
         :references;
        b=MerNr2wTeXWBSbBh9VQLCNy/wrtTyWl5oiLy1rWcf5AiS9vgb0uPpAMuNRJ/UWmssR
         wu5BrszIhiWPOtTGYuzFIYZKK44rOgbDt6Vll0Zh0v6mlhqvLg3xldqJLF/B4BW5T5JF
         5QEH4A1YtZrnHnf4cZeD8528H6sywaCNgRPu8=
Message-ID: <327858f40812050132w2b2ede16v3a03d427d3a4fb28@mail.gmail.com>
Date: Fri, 5 Dec 2008 10:32:18 +0100
From: "Leon Rosenberg" <rosenberg.leon@googlemail.com>
To: "Tomcat Users List" <users@tomcat.apache.org>
Subject: Re: jvm cowardly refuses to print a thread dump
In-Reply-To: <4938EB61.5040101@capgemini-sdm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
References: <327858f40812010617h7e39329v390ec6dca4e390a1@mail.gmail.com>
	 <0AAE5AB84B013E45A7B61CB66943C17215A3DCFD11@USEA-EXCH7.na.uis.unisys.com>
	 <6715CF65287F8F408DA109EC03AC6C0D845D92FB18@puma.melandra.net>
	 <327858f40812011004p323be166g5cc893ad4864eb78@mail.gmail.com>
	 <493539A5.8070309@capgemini-sdm.com>
	 <BLU142-W14CF3B9E324ABC7661F07BAE000@phx.gbl>
	 <4938EB61.5040101@capgemini-sdm.com>

On Fri, Dec 5, 2008 at 9:50 AM, Oliver Schoett
<oliver.schoett@capgemini-sdm.com> wrote:
> Martin Gainty wrote:
>>
>> so the solution is put all updates/inserts to the arraylist into a
>> synchronized method?
>
> You must synchronize all read and write methods, because nothing may run in
> parallel with a write method, and so read methods must be prevented from
> executing if a write method runs already.
>
> The only exception is if you can ensure that the ArrayList is read-only at
> some point in your program (e. g., after a setup phase).
>
> Arguing that the size() function cannot loop does not help, because the size
> function could be called internally in an infinite loop (this would be
> visible in the call stack).

Oliver,
I'm very sorry but i really don't see your point.
The only possible need to synchronize access to ArrayList.size is when
you a) access the list from different threads and b) need the result
to be exact. Neither was the fact in my original post, in fact, as we
already resolved it, the vm was getting out of old gen space and
afterwards just behaving weird.
In 99% of the cases you don't need to synchronize calls to ArrayList,
because usually you will use it in a local scope or single thread. And
you definitely don't need to synchronize .size(), the worst thing that
can happen is that the result is inaccurate, because another thread
just removed or added something (except for reasons stated in first
part of the mail).

regards
Leon

---------------------------------------------------------------------
To unsubscribe, e-mail: users-unsubscribe@tomcat.apache.org
For additional commands, e-mail: users-help@tomcat.apache.org