请求明确“未使用线程”的正式定义及判定场景

First off, your breakdown of the standard thread lifecycle is totally on point:
New > Runnable/Ready > Waiting/Time_waiting > Blocked [if post-wait thread can't acquire resources via notify/notifyAll] > Runnable/Ready > Dead

The tricky thing here is that "unused thread" isn’t a formally defined state in core OS or language thread specs (like POSIX threads or JVM thread models). Its meaning almost always depends on the context you’re working in—here are the most common ways it’s interpreted:

• Resource-centric OS/kernel perspective: A thread might be labeled unused if it’s in the New state but never started (e.g., you created the thread object but never called start()), or if it’s already entered the Dead state but its underlying memory/metadata hasn’t been fully reclaimed by the garbage collector or OS. These threads don’t consume CPU time or hold active locks, so they’re effectively "unused" in terms of system resource utilization.
• Application/business logic perspective: In thread pool environments (like Java’s ThreadPoolExecutor or Python’s concurrent.futures), idle threads that are in the Runnable/Ready state but have no tasks assigned to them are often called unused. This is a business-level label—they’re technically ready to run, but they’re not contributing to active work.
• Scalability research context (like your conference paper): Since you’re reading Operating system support for mitigating software scalability..., the term "unused thread" here likely refers to threads that are long-idle, consuming system resources (thread stack memory, scheduler queue slots) but not performing useful work. These threads are often targets for optimization because they waste resources that could be allocated to active tasks, hurting scalability.

To sum up: There’s no universal "official" definition, but you can pin down what counts as an unused thread by looking at whether the thread is consuming resources without contributing to active computation, and what the specific context (OS, app code, research) cares about.

内容的提问来源于stack exchange，提问作者Choudhury A. M.