線程池包含哪些狀態？

線程池狀態：

線程池的5種狀態：RUNNING、SHUTDOWN、STOP、TIDYING、TERMINATED。

見 ThreadPoolExecutor 源碼

// 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：線程池一旦被創建，就處於 RUNNING 狀態，任務數為 0，能夠接收新任務，對已排隊的任務進行處理。

 

2. SHUTDOWN：不接收新任務，但能處理已排隊的任務。調用線程池的 shutdown() 方法，線程池由 RUNNING 轉變為 SHUTDOWN 狀態。

 

3. STOP：不接收新任務，不處理已排隊的任務，並且會中斷正在處理的任務。調用線程池的 shutdownNow() 方法，線程池由(RUNNING 或 SHUTDOWN ) 轉變為 STOP 狀態。

 

4. TIDYING：

• SHUTDOWN 狀態下，任務數為 0， 其他所有任務已終止，線程池會變為 TIDYING 狀態，會執行 terminated() 方法。線程池中的 terminated() 方法是空實現，可以重寫該方法進行相應的處理。
• 線程池在 SHUTDOWN 狀態，任務隊列為空且執行中任務為空，線程池就會由 SHUTDOWN 轉變為 TIDYING 狀態。
• 線程池在 STOP 狀態，線程池中執行中任務為空時，就會由 STOP 轉變為 TIDYING 狀態。

 

5. TERMINATED：線程池徹底終止。線程池在 TIDYING 狀態執行完 terminated() 方法就會由 TIDYING 轉變為 TERMINATED 狀態。

 

狀態轉換如圖

 

JDK 源碼中的解釋如下

狀態：

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

 

 

狀態間的變化

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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