Thread Pools

A thread pool is a fixed (or bounded) set of worker threads that pull tasks from a shared queue. Instead of spawning a brand-new thread every time you've work to do, you submit the work as a task and let one of the already-running workers pick it up. This lesson covers why thread creation hurts when you do too much of it, how a pool fixes that, the four pool flavors that Executors hands you out of the box, how to size a pool for CPU-bound vs IO-bound work, and the trade-offs you sign up for when you drop down to ThreadPoolExecutor. The Executor API itself, Callable and Future, CompletableFuture, and the virtual-thread executor each get their own chapter; here we focus on the pool concept.