Olivier Langlois's blog

In my opinion, this book is better than Pthreads Programming because it goes way beyond just presenting the pthreads API. One critic I had on all the other multithreading books that I have read is that they are not covering issues with multithread programs on a SMP system. This book is actually discussing some of these issues on several pages! Beside this quality, it also covers high-level design patterns on how you can use threads such as pipelines, work crew and client/server. There is also a chapter showing how to program with thread cancellation and a section explaining how to create new synchronization objects from the primitives.

This brings me to the only problem that I can think of this book: its age. It is not totally up to date. Learning how you can build new synchronization objects by itself is a very interesting exercise but the problem is that the new synchronization objects built are the barrier and the read/write lock which have been added to the pthreads API since the book publication. Also, except for a small section describing the futur of pthreads, the newest additions to the pthread API are not described.

This book does a nice job for describing the pthread API. When I have read this book, my multithread programming experience was mainly with Win32 threads and reading this book was my first exposure to the condition synchronization objects. With the help of this book, it has been a breeze to learn how to use conditions. What is missing from this book written 10 years ago, which is also missing in all multithread books that I have read of that era, is coverage on issues with parallel processing. If all you have to do with threads is to launch a background job while keeping UI responsive or asynchronous I/O on a single core processor, you will be fine with this book.

However, if you try to crunch an array of data with multiple threads each processing their own chunk of the array, you could fall into cache line alignment problems even if your threads does not access the same memory locations. Those problems are platform dependant. I have written such a program that was working wonderfully well with a Sparc station and a PowerPC based station but once ported to a x86 architecture, the program was actually becoming slower than the single thread version. It is very hard to get it right. You have to be careful about the array alignment in memory and where the boundaries of the chunks of data that you assign to threads are. What will happen if 2 threads located on 2 different processors access to the same cache line is that one processor will have to flush that cache line back to the main memory and the other processor will have to fetch the values back from the main memory to its cache. The overhead of this is so huge that processing the array from a single thread could be faster.

I still have to find a book that addresses these problems. I expect it to come soon with dual and quad core processors becoming mainstream but this is not this book.

I had to do some text processing and I wanted to learn sed & awk so I picked this book that is, to my knowledge, the only book completely dedicated to these tools. The chapter on 'advanced' sed programming is very scary because when using 'advanced' sed features, the syntax is cryptic. It is nice to know that these features are there but I want to stay away from them and perhaps use awk or perl for the tasks that would require those 'advanced' features. Still, when you stick with the 'basic' and 'intermediate' sed features, you can do cool things easily in shell scripts.

Overall, the book was not thrilling to read but it does a good job to teach you these text processing tools.