Thursday, January 18. 2007
A few years ago, while working in the RTA, I ran into a reasonably complicated problem where a list would be traversed at two portions of the code at the same time. That is, say that I have a list A which I am traversing and performing actions on each of the contents in the list. I have reached object X and am performing an action on it. The effect of this action is to destroy object X+1 and remove it from list A. However, the iterator on list A has already grabbed a pointer to the next object (X+1), and when the loop attempts to access the memory address of X+1, it is accessing invalid memory which may cause a dreaded segmentation violation.
This problem was quite difficult to debug and eventually I managed to produce a test case which demonstrated the problem. The programming language at the time was C++, and the test case looked like this:
#include <stdio.h>
#include <list>
using ::std::list;
void pathologicalCase ( list < char * > &rList )
{
for ( list < char * >::iterator aOuterNext = rList.begin(),
aOuterIter = rList.begin(), aOuterEnd = rList.end();
aOuterIter != aOuterEnd;
aOuterIter = aOuterNext )
{
++aOuterNext;
printf ( "Outer is %s\n", (*aOuterIter ) );
for ( list < char * >::iterator aInner = rList.begin(),
aInnerNext = rList.begin(),
aInnerEnd = rList.end();
aInner != aInnerEnd;
aInner = aInnerNext )
{
++aInnerNext;
printf ( "Inner is %s\n", (*aInner) );
if ( 0 == strcmp ( *(aInner), "String B" ) )
{
free ( *(aInner) );
rList.erase ( aInner);
}
}
}
}
int main ( int argc, char **argv )
{
list < char * > aList;
aList.push_back ( strdup ( "String A" ) );
aList.push_back ( strdup ( "String B" ) );
pathologicalCase ( aList );
}
It has taken me quite some time to get the 'geshi' syntax highlighter to display the above code block correctly, so I am going to stop here for now and then post the C++ code I used to 'fix' the above problem.
I currently work for a high-tech startup called Corvil Networks. We are developing a product which is sold by Cisco as the Cisco Bandwidth Quality Manager. It's a great company to work for, and we have high hopes for version 3 of our product (in it's 3.0, 3.0.1, 3.1 etc guises). The basic software architecture of the BQM is 4 components: A C++ daemon which handles packet processing (called 'probed'), a C library which performs statistical analysis of packet data (called the 'CDK'), a Java library which handles data aggregation and a Web front end written in Java/JavaScript. All of this is backed by a Postgres database to store both configuration data and analysis data.
I am part of the team responsible for the 'probe' part of the product, and as we have recently finished the '3.0' product, we are now starting on defining what exactly the next version will look like, and what additional features we will be adding. The process for doing this is that the Product Management (PM) team provide us with Project Requirement Documents (PRDs), we analyse them and figure out how the PRDs can be implemented. The formal response to a PRD is a Functional Specification (FS) which defines what the new features will be, roughly how they will be implemented, and how they will look like to the end user (whether the user uses the Command Line Interface (CLI) or the web front-end (GUI)).
I am the team lead on writing two of these specifications, and am the probe team's representative on two others. When I started the first functional specification, I found that starting with a blank white screen in front of me somewhat intimidating, so I did a web-search for 'Functional Specification' to see if someone had some useful hints or tips about the process of writing a Functional Spec. One of the results was 'Joel on Software', someone that Caolan has often recommended that I read. I found his musings on Functional Specifications useful, and decided to follow his recommendation that the best way to get better at writing, is to write.
Hence my new resolution, which I will no doubt break in the near future: to write at least one Blog entry every week! Wish me luck!
Monday, August 28. 2006
The tag season is over! As of last saturday, our team, the Schnakey Ones have ended their season in some small amount of glory! We managed to win our league, despite finishing fourth in the table due to losing our last two games. Then, last saturday, some of us joined together with some friends from another team and went down to Cork to take part in a One Day Blitz. 
We managed to win the plate in the C division, despite battling an array of disabilities, such as hangovers, indian revenge, not knowing how to get to the rugby club and never having trained together as a team - not to mention an unhealthy dosage of pessimism about our chances!!
Despite the various injuries, and the hassle of trying to organise training and getting enough people together each week to be able to field a team, not to mention the team politics, it has been fantastic fun. I'd probably hesitate before undertaking to 'manage' a team through another season, but I definitely wouldn't hesitate to pull my boots on, tape up my fingers, put on my knee brace, strap up my ankle and head onto the pitch!
Schnake on! One league cup and one blitz plate - the double!!
Marty
Wednesday, June 14. 2006
Just over a year ago, I returned from Australia to Ireland, and resolved to treat myself to all of life's little luxuries which just aren't available to you when your house consists of a rucksack. The first of these was easy: I could leave my tooth brush next to the sink over night and be reasonably sure it would be there the next day. The second should have been just as easy: to get broadband.
Unfortunately, nothing in Ireland is easy. I did some research and discovered that BT Ireland offered the best deal. My sister, who lives in London, warned me that BT were a terrible company to have to deal with and had little or no concept of customer service. I blithely ignored this good advice, deciding that BT Ireland was a seperate company trying to break into an incumbent's market, rather than the incumbent, and that therefore surely they must have a better concept of customer service.Boy, was I wrong.
I ordered my broadband on the 13th of July, and was assured by the salesman that there was no need for me to upgrade from my expensive, charged per minute, dial-up to their flat-rate offer, as my broadband would be operational within two weeks. Three weeks later, I emailed them and asked for some hint as to whether they had even received my offer. I was assured that they had, and I could expect to be up and running within 3-4 weeks. Three weeks later, BT rang and said that they could get an engineer out to look at my line in three week's time. I said 'OK, great, so he'll get everything up and running then will he?' 'No', they said, 'He'll just check your line, we'll send out the modem 3 weeks after his visit'. This would have meant a wait of almost three months from the time I ordered to the time I had operational broadband.
Needless to say, I quickly cancelled my order and ordered broadband max from NTL instead. It was installed and operational within three days of my order, and the first three months were free for a 3MB download speed. I was pretty happy with that!
However, three weeks later, I got a letter from BT to tell me that they had cheerfully taken over my phone line from Eircom and that I was now their customer. I rang them immediately to ask 'what the!', but was told that I wasn't able to cancel my order online, and I had to cancel it in writing. This, despite the fact that they had confirmed my cancellation by email and the cancellation was still visible on their 'customer care' website. I wrote and sent a letter of cancellation the same day, and once again thought the matter was closed.
Nope. 2 months later (in mid-November now), they direct debited €122.78 out of my account, without even a little note to explain why. I rang them immediately to complain and was fobbed off, so I rang the bank and asked them to reverse the direct debit, which they couldn't, so I had to settle for merely cancelling it. I then wrote a stinker of a letter, requesting that they refund my money immediately. I got no reply, and so I started to investigate other options, such as Small Claims Court etc.
Then, in January, I got a letter from a debt collection agency telling me that I owed BT a further €58. I was a bit surprised, so I wrote them another letter requesting my money back, and also sent a complaint to their regulator, ComReg.
No replies from anyone, and then, just when I had gotten all of the forms filled out for Small Claims Court at the beginning of may, I got a cheque from them in the post for the princely sum of €115.75. I'm not entirely sure why they kept €7.03, but at this point, I don't really care. I just know that BT Ireland sucks.
Monday, April 3. 2006
We had our first training session last thursday - great fun, although hard to play a proper game of tag when the teams are made up of 3 or 4 people! Hopefully this week more people will turn up. In the pub afterwards, we went through the various other names that people have suggested, which included The Ruck Savages, We Will Ruck You, Win Or Lose - On The Booze, etc etc, and eventually settled on 'The Schnakey Ones', although since then there has been a few suggestions that maybe 'The Schnakey Few' would have been a better name.
I threw together a quick web page to keep track of what we're up to here, including a list of the panel etc. There has been some dissent amongst the team about our manager, Shane "I'm The Gaffer' Taafe, so is now planning on making everyone run laps until morale improves...
Mart
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