problems with linked lists

[Pep]

I am running the following code and am having problems with it

==========================================================================

while (running.get())
{

try
{
pp.manageClientDispatch(null);

if (pp.requestResults.size() > 0)
{
TTrequest request = pp.requestResults.poll();

if (request != null)
{
request.getMC().finishProcess();
}

}

}
catch(Throwable e)
{
logFatalToFile("TTdispatcher::run Error results size [" +
pp.requestResults.size() + "] " + e.toString(), e);
e.printStackTrace();
}

}
==========================================================================

The linked list requestResults has elements and the program runs but
suddenly starts throwing the following error from the exception catch

==========================================================================
25 Oct 2005 01:56:21 PDT: FATAL - {Thread-0} {Thread-3}
TTdispatcher::run Error results size [10] java.util.NoSuchElementException
java.util.NoSuchElementException
at java.util.LinkedList.remove(Unknown Source)
at java.util.LinkedList.removeFirst(Unknown Source)
at java.util.LinkedList.poll(Unknown Source)
at uk.co.ticketweb.TTserver.TTdispatcher.run(TTdispatcher.java:63)
at java.lang.Thread.run(Unknown Source)
==========================================================================

line 63 is the linked list poll line of code

This happens at random times in the running of the program.

Help.

Cheers,
Pep.

[Thomas Hawtin]

Pep wrote:
>
> The linked list requestResults has elements and the program runs but
> suddenly starts throwing the following error from the exception catch
>
> ==========================================================================
> 25 Oct 2005 01:56:21 PDT: FATAL - {Thread-0} {Thread-3}
> TTdispatcher::run Error results size [10] java.util.NoSuchElementException
> java.util.NoSuchElementException
> at java.util.LinkedList.remove(Unknown Source)
> at java.util.LinkedList.removeFirst(Unknown Source)
> at java.util.LinkedList.poll(Unknown Source)
> at uk.co.ticketweb.TTserver.TTdispatcher.run(TTdispatcher.java:63)
> at java.lang.Thread.run(Unknown Source)
> ==========================================================================
>
> line 63 is the linked list poll line of code
>
> This happens at random times in the running of the program.

You appear to accessing the list from multiple threads with no attempt
at thread-safety. Place synchronized blocks around operations on the
list that you want to be done together (including single method calls).

Tom Hawtin
--
Unemployed English Java programmer
http://jroller.com/page/tackline/

[Roedy Green]

On Tue, 25 Oct 2005 10:04:04 +0100, Pep <p...@nowhere.com> wrote,
quoted or indirectly quoted someone who said :

>This happens at random times in the running of the program.

Only a very few of the Collections are thread safe. See
http://mindprod.com/jgloss/threadsafety.html
--
Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.

[Pep]

Roedy Green wrote:

> On Tue, 25 Oct 2005 10:04:04 +0100, Pep <p...@nowhere.com> wrote,
> quoted or indirectly quoted someone who said :
>
>>This happens at random times in the running of the program.
>
> Only a very few of the Collections are thread safe. See
> http://mindprod.com/jgloss/threadsafety.html

Thanks for the link, I'll have a good read of that.

Foolishly I thought that the collections were thread safe :(

Cheers,
Pep.

[Pep]

Thomas Hawtin wrote:

Thanks, Roedy has pointed that out to me. I was blindly assuming that the