More Effective Use of Shared Memory on Linux

An anonymous reader writes "Making effective use of shared memory in high-level languages such as C++ is not straightforward, but it is possible to overcome the inherent difficulties. This article describes, and includes sample code for, two C++ design patterns that use shared memory on Linux in interesting ways and open the door for more efficient interprocess communication."

Comments

Re:10 fold speed improvement - Dekkers mutex ! fas

[Anonymous Coward]

Yes, some algorithms are worth remembering...

This one is worth remembering as one to avoid -- it's based on the idea of a busy-wait. Look at the while(test) { /* do nothing */ } loop and outer while loop. This should not be done. Semaphores might be slower in the specific case, but overall system performance will benefit from using best-practices.

There's a reason this algorithm lies in rest in academic journals: it's only useful as a teaching tool.

yeah, fast, and 10-fold chance of odd failures

[Krischi]

Yeah, this algorithm is fast. Too bad that it does not work. This kind of design is a common mistake by people who do not understand the intricacies of multithreaded programming. In short, it fails miserably when the CPUs are allowed to reorder loads and stores, a.k.a. pretty much any modern CPU. You need a memory barrier between setting and testing of a shared variable.

Google for Dekker's algorithm and memory barrier - you will find better explanations of the problem there than I could type up in my limited time here right now.