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If you’re experiencing an issue when using Chrome with Google Maps where typing in a location and hitting enter either does nothing or just says “Loading…” forever, you’ve very likely hit upon a bug in the Skype click-to-call extension.

Skype automatically installs this “add-on” when you install Skype and it adds links to phone numbers so that you can click them to call on Skype. Unfortunately, Google Maps seems to be triggering a bug in the extension and so it is either corrupting the data returned to the Google Maps javascript or just preventing the request from ever returning.

Following on from my last post, Jason Adam Young has some excellent advice to help you continually get better and better and building software and perhaps more importantly, be more and more valuable to whoever you happen to be working for.

This afternoon during an interview, a potential new hire at LMAX asked what LMAX could offer in the way of career progression. Since I’ve been thinking a fair bit about what comes next in my career now that I’m moving back to Australia I thought I had a pretty good answer and that it might be worth sharing here2{#footlink2:1323196996971.footnote}.

After four years living in the UK, my wife and I have decided to move back to Australia mid-February 2012 to be closer to family. As such, I’m now starting to look at job opportunities back in Oz. If you’re hiring, I’d love to hear from you and discuss how we might work together. My CV is available online to give you an idea of my experience and of course the backlog of this blog shows some of my thinking and learning throughout the years1{#footlink1:1322426906768.footnote}.

A couple of little patterns for writing long-poll based JavaScript applications have evolved in some internal apps I’ve been working on lately so I thought I’d document them for posterity.

Simple Long Poll Loop

(function($) {
    var longPollUrl = '/longpoll';

    var lastReceivedSequence;

    function poll() {
        $.ajax(longPollUrl, {
            data: { 'lastSequence': lastReceivedSequence },
            dataType: 'json',
            timeout: 15000,
            success: function(data) {
                if (!data) return;
                lastReceivedSequence = data.sequenceNumber;
                $(window).trigger('onLongPollEvent', data);
            },
            complete: poll
        });
    }
})(jQuery);

There’s very little special about this – it basically just uses jQuery to do a standard long poll. The pattern that I like is that instead of calling a particular function directly to handle events it just uses the jQuery trigger function to fire an event that can be handled by any interested code, without introducing tight coupling between the two bits of code. Listeners would receive events with:

Peter Lawrey posted an example of using the Exchanger class from core Java to implement a background logging implementation. He briefly compared it to the LMAX disruptor and since someone requested it, I thought it might be interesting to show a similar implementation using the disruptor.

Firstly, let’s revisit the very high level differences between the exchanger and the disruptor. Peter notes:

As of this morning, the Disruptor Wizard has been merged into the core LMAX Disruptor source tree. The .NET port had included the wizard style syntax for quite some time and it seemed to be generally popular, so why make people grab two jars instead of one?

I also updated it to reflect the change in terminology within the Disruptor. Instead of Consumers, there are now EventProcessors and EventHandlers. That better reflects the fact that consumers can actually add additional values to the events. Additionally, the ProducerBarrier has been merged into the ring buffer itself and the ring buffer entries are now called events. Again, that better reflects the fact that the programming model around the disruptor is most often event based.

The one problem I’ve found when upgrading to Lion is that suddenly iCal couldn’t sync to my Google Apps Calendar account – instead it repeatedly asked for the password. I’m still not really sure what caused this, but my solution was to simply delete both ~/Library/Preferences/*iCal* and ~/Library/Calendars. You really only want to do that if you exclusively use Google Calendar. If you have local calendars deleting ~/Library/Calendars will delete them.

Martin Fowler has posted an excellent overview of the LMAX architecture which helps put the use-cases and key considerations that led to the LMAX disruptor pattern in context.

Good to see some focus being put on the programming model that LMAX uses as well. While convention suggests that to get the best performance you have to make heavy use of concurrency and multithreading, the measurements LMAX did showed that the cost of contention and communication between threads was too great. As such, the programming model at LMAX is largely single-threaded, achieving the best possible performance while avoiding the complexities of multithreaded programming.

The LMAX disruptor is an ultra-high performance, low-latency message exchange between threads. It’s a bit like a queue on steroids (but quite a lot of steroids) and is one of the key innovations used to make the LMAX exchange run so fast. There is a rapidly growing set of information about what the disruptor is, why it’s important and how it works – a good place to start is the list of articles and for the on-going stuff, follow LMAX Blogs. For really detailed stuff, there’s also the white paper (PDF).

As my colleague and favorite debating opponent Danny Yates noted:

We got into a bit of a debate at work recently. It went a bit like this:

“Gah! Why do we have this interface when there is only a single implementation?”

(The stock answer to this goes:) “Because we need the interface in order to mock this class in our tests.”

“Oh no you don’t, you can use the FingleWidget [insert appropriate technology of your mocking framework of choice here – e.g. JMock ClassImposteriser]! I’m smarter than you!”

“Well, yes, you can. But if you’ve correctly followed Design for Extension principles, you’ve made the class final, right? And you definitely can’t mock that! Hah! I’m smarter than you!”

“Ah ha! But you could always use the JDave Unfinaliser Agent! I’m so smart it hurts!”

Joyously, it looks like iOS 5 fixes the issues with contentEditable not working correctly in Mobile WebKit. A patch has landed in TinyMCE to enable the editor to work there. Great news.

Hopefully the changes to WebKit can flow through to Android as well.