threads

Threads look deceptively simple — create a few, share some memory, done. In practice, shared mutable state is a minefield: race conditions, non-deterministic output, and bugs that vanish under a debugger. This lesson dissects concurrency vs parallelism, why `count++` is three operations the CPU can interleave, Amdahl's law, and what a critical section actually means.

How CUDA carves a problem into a grid of blocks of threads. Host vs device code, the __global__ qualifier, the launch syntax, and how every thread figures out which slice of data it owns.