源码阅读 - 线程池：线程池原理（二）线程池构造函数解析

本文链接： https://blog.csdn.net/lidelin10/article/details/100031286

一、基本构造函数

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;
}

corePoolSize：核心线程数量；
maximumPoolSize：最大线程数量。当工作任务队列饱和时，将会增加工作线程数量，该值为增长的最大值；
满足条件：maximumPoolSize >= corePoolSize；
keepAliveTime：空闲线程的超时时间。默认是指超过corePoolSize的部分线程，但如果设置allowsCoreThreadTimeOut(true)，只要工作线程数量大于1，都会对空闲线程进行超时检测。
unit：keepAliveTime的单位，最后都会转换成纳秒。
workQueue：工作线程数量超过核心线程数量时，会将任务加入工作任务队列。
threadFactory：创建线程的工厂方法，每次创建线程时调用threadFactory的newThread方法
handler：拒绝策略，当线程池饱和或者线程池的状态不支持提交新的任务将会调用其reject方法，默认实现为抛出异常。

下面是一些参数数量较少的构造函数，当本质都是调用了上面的构造函数：

public ThreadPoolExecutor(int corePoolSize,
                          int maximumPoolSize,
                          long keepAliveTime,
                          TimeUnit unit,
                          BlockingQueue<Runnable> workQueue,
                          RejectedExecutionHandler handler) {
    this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
         Executors.defaultThreadFactory(), handler);
}

public ThreadPoolExecutor(int corePoolSize,
                          int maximumPoolSize,
                          long keepAliveTime,
                          TimeUnit unit,
                          BlockingQueue<Runnable> workQueue,
                          ThreadFactory threadFactory) {
    this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
         threadFactory, defaultHandler);
}

public ThreadPoolExecutor(int corePoolSize,
                          int maximumPoolSize,
                          long keepAliveTime,
                          TimeUnit unit,
                          BlockingQueue<Runnable> workQueue) {
    this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
         Executors.defaultThreadFactory(), defaultHandler);
}

二、一些重要的变量

//工作任务队列
private final BlockingQueue workQueue;
//操纵工作线程集合（workers）的锁
private final ReentrantLock mainLock = new ReentrantLock();
//工作线程集合，操作时，需要获取mainLock
private final HashSet workers = new HashSet();
//是否允许核心线程超时退出
private volatile boolean allowCoreThreadTimeOut;

//高3位是线程池的运行状态，低29位为线程数量
private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
private static final int COUNT_BITS = Integer.SIZE - 3;
//工作线程数量的最大值,2^29-1
private static final int CAPACITY   = (1 << COUNT_BITS) - 1;

//线程池的五种状态
private static final int RUNNING    = -1 << COUNT_BITS;
private static final int SHUTDOWN   =  0 << COUNT_BITS;//调用shutdown，等待队列任务执行完成
private static final int STOP       =  1 << COUNT_BITS;//调用shutdownNow ，直接返回，不等待队列中任务执行完成
private static final int TIDYING    =  2 << COUNT_BITS;//工作线程集合为空
private static final int TERMINATED =  3 << COUNT_BITS;//terminated回调完成//1610612736

其中ctl可以联系ConcurrentHashMap中的ctl，doug lea都是用这个同名参数来存储状态。

源码阅读 - 线程池： 线程池原理（二）线程池构造函数解析

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源码阅读 - 线程池：线程池原理（二）线程池构造函数解析