JDK线程池框架Executor源码阅读

Posted 2020-07-30 Q_Quan

Executor框架

Executor

ExecutorService

AbstractExecutorService

ThreadPoolExecutor

ThreadPoolExecutor继承AbstractExecutorService，是一个线程池的具体的实现

主要成员

1. ctl

    private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
    private static final int COUNT_BITS = Integer.SIZE - 3;
    private static final int CAPACITY   = (1 << COUNT_BITS) - 1;

    // 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;

 

AtomicInteger类型的私有变量ctl，使用高3bit表示线程池状态runState，低29bit来表示线程池线程总数。可见，Executor线程数量是有限制的，最多(2^29)-1个(about 500 million)。

前3bit表示线程池生命周期的5个状态，RNUNING，SHUTDOWN，STOP，TIDYING，TERMINATED。注释中给出了线程池所有可能的状态转化，随着生命周期的变更，几个状态从小到大赋值。

2. workQueue

    private final BlockingQueue<Runnable> workQueue;

存储待执行tasks的任务队列。

3. workers

    private final HashSet<Worker> workers = new HashSet<Worker>();

工作线程集合。

4. mainLock

    private final ReentrantLock mainLock = new ReentrantLock();

访问workers时必须持有的锁。

主要方法

总结

ScheduleExecutorService

Executors

总结