Programmer XiaoFu

May 27, 2026 · Backend Development

Why Does a ThreadPool Queue Tasks Even When Max Threads Are Idle?

The article explains why Java's ThreadPoolExecutor places tasks into a queue before creating non‑core threads, discusses the cost of thread creation and CPU contention, illustrates the design with a bank‑counter analogy, and shows how Tomcat customizes the queue to prioritize thread creation for low‑latency web workloads.