1. 入门的，《The Little Book of Semaphores》

The Little Book of Semaphores is a free textbook that introduces the principles of synchronization for concurrent programming.

The approach of this book is to identify patterns that are useful for a variety of synchronization problems and then show how they can be assembled into solutions. After each problem, the book offers a hint before showing a solution, giving students a better chance of discovering solutions on their own.

The book covers the classical problems, including “Readers-writers,” “Producer-consumer”, and “Dining Philosophers.” In addition, it collects a number of not-so-classical problems, some written by the author and some by other teachers and textbook writers.
可以在它的官方网站下载：http://greenteapress.com/semaphores/

2. RCU 的作者，大牛 Paul E. McKenney 写的书，《Is Parallel Programming Hard, And, If So, What Can You Do About It?》。这个比较猛，我还没时间看。它也是免费的，英文版可以在这里下载：

git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/perfbook.git

现在已经被翻译成中文了，叫《深入理解并行编程》：

http://download.csdn.net/detail/xiebaoyou/3552357

我在南京和布拉格的时候见过 Paul E. McKenney，他是一个非常和蔼、热心的人，没有一点儿牛人的架子。:-)