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Showing posts from September, 2013

This Blog Has Moved!

Right, so yes, five years ago I moved to github pages, and never bothered to redirect any of these pages there. Now I've moved on from there, and... Finally I am using my real domain, trishagee.com . My blog is now at trishagee.com/blog .  See you there!
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Kids These Days

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I'm a great believer in getting kids to code early - after all, I'm of that generation that was taught  at the age of 9.  There are quite a few approaches to teaching today's kids in an engaging way, but I'm a bit wary of the sandbox solutions that teach kids things like how to navigate a virtual thingie around the screen, or lets them create things in a limited virtual world.  I don't think kids will easily make the leap between these sort of games to seeing the full potential of programming - they're too limited and have no context for the kids.  It's just another game. Kids need to understand how programming fits into their world, they need to understand the context of coding, if they're going to fall in love with it. I like Jason Gorman 's comparison of programming to music.  Most people learn an instrument because they want to make the sort of music they hear on the radio.  But you give them a recorder and teach them to play &quo
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JavaZone, Oslo

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For the rest of 2013, this blog will mostly be masquerading as a travel blog. This week I've been in Oslo, and I liked it.  Actually, you'll be hard-pushed to find somewhere I've visited that I didn't like in one way or another, but Oslo does make my "definitely going back there" list.  If Seville, where I've been for the last month, is stuffed full of History, Oslo is overflowing with Geography.  I've noticed a pattern in that my favourite places were sunny when I visited them first, which subconsciously prompts me to love them (as a vitamin-D-deprived Englishwoman).  Oslo was NOT one of those places, it was overcast and extremely chilly compared to the south of Spain.  But the countryside around it is really pretty, and it's very green and mountainy and watery.  Not like Spain, or the UK for that matter. I found the Norwegians really friendly, and as with all the Nordic countries their English is better than you'll find in an int
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Popular posts from this blog

Dissecting the Disruptor: What's so special about a ring buffer?

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Recently we open sourced the LMAX Disruptor , the key to what makes our exchange so fast.  Why did we open source it?  Well, we've realised that conventional wisdom around high performance programming is... a bit wrong. We've come up with a better, faster way to share data between threads, and it would be selfish not to share it with the world.  Plus it makes us look dead clever. On the site you can download a technical article explaining what the Disruptor is and why it's so clever and fast.  I even get a writing credit on it, which is gratifying when all I really did is insert commas and re-phrase sentences I didn't understand. However I find the whole thing a bit much to digest all at once, so I'm going to explain it in smaller pieces, as suits my  NADD audience. First up - the ring buffer.  Initially I was under the impression the Disruptor was just the ring buffer.  But I've come to realise that while this data structure is at the heart of the patte
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Dissecting the Disruptor: Writing to the ring buffer

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This is the missing piece in the end-to-end view of the Disruptor.  Brace yourselves, it's quite long.  But I decided to keep it in a single blog so you could have the context in one place. The important areas are: not wrapping the ring; informing the consumers; batching for producers; and how multiple producers work. ProducerBarriers The Disruptor code has interfaces and helper classes for the Consumer s, but there's no interface for your producer, the thing that writes to the ring buffer.  That's because nothing else needs to access your producer, only you need to know about it.  However, like the consuming side, a ProducerBarrier is created by the ring buffer and your producer will use this to write to it. Writing to the ring buffer involves a two-phase commit.  First, your producer has to claim the next slot on the buffer.  Then, when the producer has finished writing to the slot, it will call commit on the ProducerBarrier . So let's look at the first bi
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Dissecting the Disruptor: How do I read from the ring buffer?

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The next in the series of understanding the Disruptor pattern developed at LMAX . After the last post we all understand ring buffers and how awesome they are.  Unfortunately for you, I have not said anything about how to actually populate them or read from them when you're using the Disruptor. ConsumerBarriers and Consumers I'm going to approach this slightly backwards, because it's probably easier to understand in the long run.  Assuming that some magic has populated it: how do you read something from the ring buffer? (OK, I'm starting to regret using Paint/ Gimp .  Although it's an excellent excuse to purchase a graphics tablet if I do continue down this road.  Also UML gurus are probably cursing my name right now.) Your Consumer is the thread that wants to get something off the buffer.  It has access to a ConsumerBarrier , which is created by the RingBuffer and interacts with it on behalf of the Consumer .  While the ring buffer obviously needs a se
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