Imagine a configuration cache that gets read by thousands of threads every second but only gets updated once every few minutes. If you protect it with a regular mutex, every single read blocks every other read, even though reading doesn't modify anything.

With a thousand concurrent readers, you've essentially serialized operations that could safely run in parallel. Your throughput tanks, latency spikes, and the mutex becomes the bottleneck in an otherwise scalable system.

This is the exact problem read-write locks were designed to solve.

This chapter explores how read-write locks work internally, when they provide real benefits versus when they add unnecessary overhead, and the subtle pitfalls that can turn a performance optimization into a debugging nightmare.

What is a Read-Write Lock?