看 leveldb 源码中遇到的，关于 lock-free 和 wait-free..感觉这个讲得不错，我试着翻译一下？
There are two types of non-blocking thread synchronization algorithms - lock-free, and wait-free. Their meaning is often confused. In lock-free systems, while any particular computation may be blocked for some period of time, all CPUs are able to continue performing other computations. To put it differently, while a given thread might be blocked by other threads in a lock-free system, all CPUs can continue doing other useful work without stalls. Lock-free algorithms increase the overall throughput of a system by occassionally increasing the latency of a particular transaction. Most high- end database systems are based on lock-free algorithms, to varying degrees.
有两种无阻塞线程同步算法，一种是 lock-free，一种是 wait-free，它们的含义经常被搞混。在一个 lock-free 系统中，尽管某个特定的计算会被阻塞一段时间，所有 CPU 还是能够继续其他计算。换一种说法，尽管在一个 lock-free 系统中，一个线程可能被其他线程阻塞，所有 CPU 仍然可以继续做其他工作而不停顿。lock-free 算法通过偶尔增加某个特定事务的延迟，提高了系统总体的吞吐率。大多数高端数据库系统都在某种程度上基于 lock-free 算法。
By contrast, wait-free algorithms ensure that in addition to all CPUs continuing to do useful work, no computation can ever be blocked by another computation. Wait-free algorithms have stronger guarantees than lock-free algorithms, and ensure a high thorughput without sacrificing latency of a particular transaction. They’re also much harder to implement, test, and debug. The lockless page cachepatches to the Linux kernel are an example of a wait-free system.
与此相反，wait-free 算法除了保证所有 CPU 继续做其他工作以外，还保证不会有任何计算被另一个计算阻塞。wait-free 算法比 lock-free 算法有更强的保证：在不牺牲某个特定事务延迟的前提下拥有更高的吞吐率。也正因如此，wait-free 算法更加难以实现、测试和调试。Linux 内核的无锁页面缓存（？）就是一个 wait-free 系统的例子。
In a situation where a system handles dozens of concurrent transactions and has soft latency requirements, lock-free systems are a good compromise between development complexity and high concurrency requirements. A database server for a website is a good candidate for a lock-free design. While any given transaction might block, there are always more transactions to process in the meantime, so the CPUs will never stay idle. The challenge is to build a transaction scheduler that maintains a good mean latency, and a well bounded standard deviation.
在一个系统处理几十个并发事务并且对延迟要求不高的情况下，lock-free 系统是开发复杂性和高并发要求之间的良好折衷。一个网站的数据库服务器就是 lock-free 系统很好的例子。尽管某个特定的事务可能被阻塞，但同时总有更多的事务要处理，所以 CPU 永远不会空闲。面临的挑战是构建一个事务调度器，从而获得尽可能低的平均延迟和有界的标准偏差。
In a scenario where a system has roughly as many concurrent transactions as CPU cores, or has hard real-time requirements, the developers need to spend the extra time to build wait-free systems. In these cases blocking a single transaction isn’t acceptable - either because there are no other transactions for the CPUs to handle, minimizing the throughput, or a given transaction needs to complete with a well defined non-probabilistic time period. Nuclear reactor control software is a good candidate for wait-free systems.
在一个并发事务数量与 CPU 内核数量大致相同的场景中，或者在有硬实时要求的场景中，开发人员需要花费额外的时间来构建 wait-free 系统。在这种情况下，阻塞单个事务是不可接受的：要么是因为 CPU 没有其他事务要处理，从而降低了吞吐量；要么是给定的事务需要在一个确定的时间段内完成（相对比较确定的时间的意思？）。核反应堆控制软件就是 wait-free 系统很好的例子。