Multi-threaded bugs vanish under the debugger. Stack traces lie. Variables seem to change value between two prints. The GDB techniques that actually find races: thread-pinned breakpoints, non-stop mode, watchpoints, TSan-then-GDB, and rr.
Three primitives cover almost every locking decision: spinlocks, mutexes, and futexes. They solve the same problem with very different cost models — burning CPU vs trapping to the kernel vs the hybrid approach modern mutexes actually use.
Compilers reorder. CPUs reorder. Single-threaded code never notices — multi-threaded code crashes mysteriously. A clear walk through acquire and release semantics, what the hardware actually does, and the spinlock that ties it all together.
Two threads, two variables, no shared state — and a 4x slowdown. False sharing is the cache coherence tax you pay when unrelated data lands on the same 64-byte line. How to spot it and fix it.
Inside ThreadSafeCLogger: how to build a high-performance logging library that doesn't serialize your threads, using per-thread SPSC ring buffers and careful memory ordering.