线程池包含哪些状态?

2019-09-10   阅读(271)  

线程池状态:

线程池的5种状态:RUNNING、SHUTDOWN、STOP、TIDYING、TERMINATED。

见 ThreadPoolExecutor 源码

// runState is stored in the high-order bits
    private static final int RUNNING    = -1 << COUNT_BITS;
    private static final int SHUTDOWN   =  0 << COUNT_BITS;
    private static final int STOP       =  1 << COUNT_BITS;
    private static final int TIDYING    =  2 << COUNT_BITS;
    private static final int TERMINATED =  3 << COUNT_BITS;

 

1. RUNNING:线程池一旦被创建,就处于 RUNNING 状态,任务数为 0,能够接收新任务,对已排队的任务进行处理。

 

2. SHUTDOWN:不接收新任务,但能处理已排队的任务。调用线程池的 shutdown() 方法,线程池由 RUNNING 转变为 SHUTDOWN 状态。

 

3. STOP:不接收新任务,不处理已排队的任务,并且会中断正在处理的任务。调用线程池的 shutdownNow() 方法,线程池由(RUNNING 或 SHUTDOWN ) 转变为 STOP 状态。

 

4. TIDYING:

  • SHUTDOWN 状态下,任务数为 0, 其他所有任务已终止,线程池会变为 TIDYING 状态,会执行 terminated() 方法。线程池中的 terminated() 方法是空实现,可以重写该方法进行相应的处理。
  • 线程池在 SHUTDOWN 状态,任务队列为空且执行中任务为空,线程池就会由 SHUTDOWN 转变为 TIDYING 状态。
  • 线程池在 STOP 状态,线程池中执行中任务为空时,就会由 STOP 转变为 TIDYING 状态。

 

5. TERMINATED:线程池彻底终止。线程池在 TIDYING 状态执行完 terminated() 方法就会由 TIDYING 转变为 TERMINATED 状态。

 

状态转换如图

 

JDK 源码中的解释如下

状态:

The runState provides the main lifecyle control, taking on values:

  RUNNING:  Accept new tasks and process queued tasks
  SHUTDOWN: Don't accept new tasks, but process queued tasks
  STOP:     Don't accept new tasks, don't process queued tasks,
            and interrupt in-progress tasks
  TIDYING:  All tasks have terminated, workerCount is zero,
            the thread transitioning to state TIDYING
            will run the terminated() hook method
  TERMINATED: terminated() has completed

 

状态间的变化

RUNNING -> SHUTDOWN
   On invocation of shutdown(), perhaps implicitly in finalize()
(RUNNING or SHUTDOWN) -> STOP
   On invocation of shutdownNow()
SHUTDOWN -> TIDYING
   When both queue and pool are empty
STOP -> TIDYING
   When pool is empty
TIDYING -> TERMINATED
   When the terminated() hook method has completed

Threads waiting in awaitTermination() will return when the
state reaches TERMINATED.

 

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