Rust's ownership and borrowing system is one of its superpowers—it eliminates entire classes of bugs like dangling pointers and data races at compile time. But for many newcomers, lifetimes feel like the most confusing part. You might have read that "lifetimes mark how long a reference lives," but that explanation often falls short.

Have you ever looked at a complex piece of code and wondered, "Does the CPU truly execute this exactly as I've written it?" The surprising answer, on modern systems, is a resounding no. In their relentless pursuit of performance, CPUs and compilers have become masters of illusion, rearranging our instructions to run them faster. This is the world of Out-of-Order Execution (OoOE).

If you've spent any time in the depths of the Linux kernel, you've undoubtedly encountered a synchronization mechanism called RCU (Read-Copy-Update). It's a powerful tool that enables blazingly fast read performance under the right circumstances. While there are now many flavors of RCU (like Sleepable RCU, or PREEMPT_RT), it all started with a brilliant, core idea often called "Classic RCU".

This post is a deep dive into that classic design: its history, its soul, and why it remains a cornerstone of high-performance computing.

Basic part of any event driven, non-blocking program is event loop. Many mechanisms are provided by operating systems to implement this IO pattern. Some of them are common and some of them are OS-specific.

Let's review the event loop of lighttpd.