原文

/*
* Proceed in 3 steps:
*
* 1. If fewer than corePoolSize threads are running, try to
* start a new thread with the given command as its first
* task.  The call to addWorker atomically checks runState and
* workerCount, and so prevents false alarms that would add
* threads when it shouldn't, by returning false.
*
* 2. If a task can be successfully queued, then we still need
* to double-check whether we should have added a thread
* (because existing ones died since last checking) or that
* the pool shut down since entry into this method. So we
* recheck state and if necessary roll back the enqueuing if
* stopped, or start a new thread if there are none.
*
* 3. If we cannot queue task, then we try to add a new
* thread.  If it fails, we know we are shut down or saturated
* and so reject the task.
*/

译文

  1. 核心线程创建阶段
    当活跃线程数 < 核心线程数(corePoolSize)时：
    • 尝试以原子操作启动新工作线程
    • 新线程将指定任务作为首任务执行
    • 通过addWorker方法的原子校验机制，同时检测：
      ▸ 线程池运行状态(runState)
      ▸ 当前工作线程数(workerCount)
    • 防止因状态突变导致虚假线程创建（如检查期间线程池意外关闭）
  2. 任务队列缓冲阶段
    当任务成功入队后：
    • 需进行二次状态验证：
      ▶ 校验是否存在线程意外终止（检查后消亡）
      ▶ 确认线程池未在此方法执行期间关闭
    • 根据验证结果执行：
      ▶ 若线程池已停止：执行任务回滚操作
      ▶ 若无存活线程：启动新线程处理队列
  3. 饱和处理阶段
    当任务队列已满时：
    • 尝试创建非核心线程扩展处理能力
    • 若线程创建失败，表明：
      ▶ 线程池已执行shutdown()
      ▶ 或已达最大线程数(maximumPoolSize)
    • 最终执行任务拒绝策略