The Art of Multiprocessor Programming, Revised Reprint

17

Barriers

17.1 Introduction

Imagine you are writing the graphical display for a computer game. Your program prepares a sequence of frames to be displayed by a graphics package (perhaps a hardware coprocessor). This kind of program is sometimes called a soft real-time application: real-time because it must display at least 35 frames per second to be effective, and soft because occasional failure is not catastrophic. On a single-threaded machine, you might write a loop like this:

while (true) {

 frame.prepare();

 frame.display();

 }

If, instead, you have n parallel threads available, then it makes sense to split the frame into n disjoint parts, and to have each thread prepare its own part in parallel with the others.

int me = ThreadID.get(); ...