直接断点进去：

@Test
public void testKeepAliveTime3() {//生存时间 - 针对救急线程ThreadPoolExecutor executor = new ThreadPoolExecutor(1, 2, 10, TimeUnit.SECONDS, new SynchronousQueue<>());
}

public ThreadPoolExecutor(int corePoolSize,int maximumPoolSize,long keepAliveTime,TimeUnit unit,BlockingQueue<Runnable> workQueue,ThreadFactory threadFactory,RejectedExecutionHandler handler) {if (corePoolSize < 0 ||maximumPoolSize <= 0 ||maximumPoolSize < corePoolSize ||keepAliveTime < 0)throw new IllegalArgumentException();if (workQueue == null || threadFactory == null || handler == null)throw new NullPointerException();this.acc = System.getSecurityManager() == null ?null :AccessController.getContext();this.corePoolSize = corePoolSize;this.maximumPoolSize = maximumPoolSize;this.workQueue = workQueue;this.keepAliveTime = unit.toNanos(keepAliveTime);this.threadFactory = threadFactory;this.handler = handler;
}

这里点进去看成员变量private volatile long keepAliveTime;的注释：

* Timeout in nanoseconds for idle threads waiting for work.
* Threads use this timeout when there are more than corePoolSize present or if allowCoreThreadTimeOut. Otherwise they wait forever for new work.

对于英语好的同学应该是秒懂了

看不懂就翻译：

* 等待工作的空闲线程超时（以纳秒为单位）。
当存在超过 corePoolSize 或允许 CoreThreadTimeOut 时，线程使用此超时。否则，他们会永远等待新的工作。