To many people out there, parallel programming may not sound very useful, and actually pretty complicated. However, everybody expects processors to have several cores and software to make use of them. The whole purpose of parallel programming is to leverage the capabilities of multi-core processors, but this comes with a cost: we need to rethink our way of programming, moving from the old single-threaded or "a thread per task" programs to applications that describe their work-flow in tasks that can be concurrently processed: what is called task-based programming.
This may sound difficult, but it is necessary to produce code that can actually use several cores, and also scale properly (ie. keep a decent performance level) from single-core processors to computer grids with hundreds of cores. The problem of multi-thread apps made by hand is that often, threads are planned per task, but even worse, the number of logical threads in the program is not equal to the number of physical threads on the CPU, but to the number of tasks, which is fixed. This means the program does not scale at all, unless thread pools are created and managed by hand, which means a huge code overhead for the thread pool management system. Besides, this means you still have to do load balancing between threads on your own, which is again a difficult task.
To the difference of multi-threaded apps with synchronisation code, the goal here is to leave all thread management and task assignment to a specifically built library. In this article, I am going to explain the very basics of Intel Threading Building Blocks, most likely one of the most efficient and simple multi-core programming libraries in the wild.
Published Nov. 13, 2011 by read more