Memory Consistency Models: A Tutorial

Memory Consistency Models: A Tutorial There are, of course, only two hard things in computer science: cache invalidation, naming things, and off-by-one errors. But there is another hard problem lurking amongst the tall weeds of computer science: seeing things in order. Whether it be sorting, un-sorting, or tweeting, seeing things in order is a challenge for the ages. One common ordering challenge is memory consistency, which is the problem of defining how parallel threads can observe their shared memory state. There are many resources on memory consistency, but most are either slides (like mine!) or dense tomes. My goal is to produce a primer, and motivate why memory consistency is an issue for multicore systems. For the details, you should certainly consult these other excellent sources. Making threads agree Consistency models deal with how multiple threads (or workers, or nodes, or replicas, etc.) see the world. Consider this simple program, running two threads, and where A and B ... Read full article.