Sunday, November 15, 2009

Article at CodeProject C++ Lock Free Circular Queue

I attended Herb Sutter's Effective Concurrency Seminar (Europe 2009), a very inspiring seminar where he approached multi-core targeted programming. One thing we worked with was the dangers of Lock-Free programming and hazards of volatile in C++.

I got curious since I've seen a couple of simple single producer -> single consumer Circular Queue implementations that are implemented as Lock-Free and using just that, the important state variables defined as volatile. So how come they work (being used for years), or do they?

Volatile as you might know is not intended for multi-threading but for accessing hardware devices (and more). It turns out that volatile plays a minor role and that it's mostly the compiler and computer platform that decides whether or not this kind of Circular Queues will be safe to use.

I have implemented a thread safe circular queue in C++ and explain in this article when it works and when it will not work. This is an area outside the scope of the C++ standard (until C++0x) and is suitable for (at least) x86 or x64 platforms.

For those of you who want to read up on the inner workings of the Circular Queue, I have provided a short description of it and my implementation. For those of you who are already familiar with it and just want to know if this thread safe circular queue is for real, just go straight to the Implementation section. You can find the whole article either at CodeProject or at my page.

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