Parallelization

Revisiting randomness

By jonskeet

Almost every Stack Overflow question which includes the words "random" and "repeated" has the same basic answer. It’s one of the most common "gotchas" in .NET, Java, and no doubt other platforms: creating a new random number generator without specifying a seed will depend on the current instant of time. The current time as measured by the computer doesn’t change very often compared with how often you can create and use a random number generator – so code which repeatedly creates a new instance of Random and uses it once will end up showing a lot of repetition. One common … Continue reading Revisiting randomness

Iterating atomically

By jonskeet

The IEnumerable<T> and IEnumerator<T> interfaces in .NET are interesting. They crop up an awful lot, but hardly anyone ever calls them directly – you almost always use a foreach loop to iterate over the collection. That hides all the calls to GetEnumerator(), MoveNext() and Current. Likewise iterator blocks hide the details when you want to implement the interfaces. However, sometimes details matter – such as for this recent Stack Overflow question. The question asks how to create a thread-safe iterator – one that can be called from multiple threads. This is not about iterating over a collection n times independently … Continue reading Iterating atomically

Recent activities

By jonskeet

It’s been a little while since I’ve blogged, and quite a lot has been going on. In fact, there are a few things I’d have blogged about already if it weren’t for “things” getting in the way. Rather than writing a whole series of very short blog posts, I thought I’d wrap them all up here… C# in Depth: next MEAP drop available soon – Code Contracts Thanks to everyone who gave feedback on my writing dilemma. For the moment, the plan is to have a whole chapter about Code Contracts, but not include a chapter about Parallel Extensions. My … Continue reading Recent activities

Buffering vs streaming benchmark: first results

By jonskeet

My poor laptop’s had a busy weekend. It’s run 72 tests, rebooting between each test. Most of these tests have kept both the CPU and disk busy for a lot of the time. I expect to update this blog post with more numbers – and possibly more strategies – as time goes on, but I wanted to get the numbers out as quickly as possible. Graphs should be coming when I’ve got a decent network to experiment with Google graphing. Source code and setup While I don’t really expect anyone else to sacrifice their computer for the best part of … Continue reading Buffering vs streaming benchmark: first results

Benchmarking IO: buffering vs streaming

By jonskeet

I mentioned in my recent book review that I was concerned about a recommendation to load all of the data from an input file before processing all of it. This seems to me to be a bad idea in an age where Windows prefetch will anticipate what data you need next, etc – allowing you to process efficiently in a streaming fashion. However, without any benchmarks I’m just guessing. I’d like to set up a benchmark to test this – it’s an interesting problem which I suspect has lots of nuances. This isn’t about trying to prove the book wrong … Continue reading Benchmarking IO: buffering vs streaming

DotNetRocks interview

By jonskeet

Last Monday evening I had a chat with the guys from DotNetRocks, and today the show has gone live. I wouldn’t claim to have said anything particularly earth-shattering, and regular readers will probably be familiar with many of the themes anyway, but I thoroughly enjoyed it and hope you will too. Amongst other things, we talked about: Protocol buffers Implicit typing and anonymous types Why it doesn’t bother me that Office hasn’t been ported to .NET C# 4 My wishlist for C# Threading and Parallel Extensions Working for Google How to learn LINQ C# in Depth Feedback welcome. And yes, … Continue reading DotNetRocks interview

Parallel Extensions June CTP

By jonskeet

Either my timing is great or it’s lousy – you decide. Yesterday I posted about parallelising Conway’s Life – and today the new CTP for the Parallel Extensions library comes out! The bad news is that it meant I had to run all the tests again… the good news is that it means we can see whether or not the team’s work over the last 6 months has paid off. Breaking change The only breaking change I’ve seen is that AsParallel() no longer takes a ParallelQueryOptions parameter – instead, you call AsOrdered() on the value returned from AsParallel(). It was … Continue reading Parallel Extensions June CTP

More parallelisation fun: Conway’s Game of Life

By jonskeet

Okay, so I’ve probably exhausted the Mandelbrot set as a source of interest, at least for the moment. However, every so often someone mentions something or other which sounds like a fun exercise in parallelisation. The latest one is Conway’s Game of Life. Like the Mandelbrot set, this is something I used to play with when I was a teenager – and like the Mandelbrot set, it’s an embarrassingly parallel problem. As before, I’ve written a few implementations but not worked excessively hard to optimise. All my tests were performed with a game board of 1000×500 cells, displaying at one … Continue reading More parallelisation fun: Conway’s Game of Life

Mandelbrot revisited – benchmark edition

By jonskeet

I’ve had fun with the Mandelbrot set in this blog before, using it as an example of an embarrassingly parallelisable problem and demonstrating Parallel LINQ with it. This morning, over breakfast, I described the problem to Christian Brunschen, a colleague of mine who has some parallelisation experience through implementing OpenMP in a portable manner. He immediately suggested a few possible changes to the way that I’ve approached things. Given the number of different attempts I’ve now had, I thought it would make sense to write a litte benchmarking app which could easily be expanded as further implementations were considered. The … Continue reading Mandelbrot revisited – benchmark edition

Visualising the Mandelbrot set with LINQ – yet again

By jonskeet

I’ve been thinking about ranges again, particularly after catching a book error just in time, and looking at Marc’s generic complex type. It struck me that my previous attempts were all very well, and demonstrated parallelisation quite neatly, but weren’t very LINQy. In particular, they certainly didn’t use LINQ for the tricky part in the same way that Luke Hoban’s ray tracer does. The thing is, working out the “value” of a particular point in the Mandelbrot set visualisation is actually quite well suited to LINQ: Start with a complex value Apply a transformation to it (square the current value, … Continue reading Visualising the Mandelbrot set with LINQ – yet again