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:

This approach has similar principles to the Disruptor. No GC using recycled, pre-allocated buffers and lock free operations (The Exchanger not completely lock free and doesn’t busy wait, but it could)

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.

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).