日常记录——多线程与高并发—ThreadPoolExecutor源码解析

package java.util.concurrent;

import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.*;

public class ThreadPoolExecutor extends AbstractExecutorService {
    //高3位来表示线程池的运行状态, 用低29位来表示线程池内有效线程数量。 初始状态为RUNNING
    private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
    //记录线程数量的占ctl的位数
    private static final int COUNT_BITS = Integer.SIZE - 3;
    //线程池最大可以容纳的线程数量
    private static final int CAPACITY   = (1 << COUNT_BITS) - 1;

    // 表示运行状态
    private static final int RUNNING    = -1 << COUNT_BITS;
    //不接受新的任务，但是可以处理任务队列里的任务
    private static final int SHUTDOWN   =  0 << COUNT_BITS;
    //不接受新的任务，不处理阻塞队列里的任务，中断正在处理的任务。
    private static final int STOP       =  1 << COUNT_BITS;
    //表示过渡状态。此时所有的任务都执行完毕，当前线程池已经没有有效的线程。
    private static final int TIDYING    =  2 << COUNT_BITS;
    //表示终止状态
    private static final int TERMINATED =  3 << COUNT_BITS;

    //获取线程池状态
    private static int runStateOf(int c)     { return c & ~CAPACITY; }
    //获取线程数量
    private static int workerCountOf(int c)  { return c & CAPACITY; }
    //基于线程池状态和线程数量生成一个ctl值。
    private static int ctlOf(int rs, int wc) { return rs | wc; }
	//线程池状态小于s
    private static boolean runStateLessThan(int c, int s) {
        return c < s;
    }
	//线程池状态大于等于s
    private static boolean runStateAtLeast(int c, int s) {
        return c >= s;
    }
	//线程池状态是否在运行
    private static boolean isRunning(int c) {
        return c < SHUTDOWN;
    }
	//尝试CAS递增ctl的工作线程数量。
    private boolean compareAndIncrementWorkerCount(int expect) {
        return ctl.compareAndSet(expect, expect + 1);
    }

    //尝试CAS递减ctl的工作线程数量。
    private boolean compareAndDecrementWorkerCount(int expect) {
        return ctl.compareAndSet(expect, expect - 1);
    }

    //减少ctl的工作线程。仅在线程突然终止时调用此方法。一直减到 失败为止
    private void decrementWorkerCount() {
        do {} while (! compareAndDecrementWorkerCount(ctl.get()));
    }

    //任务队列
    private final BlockingQueue<Runnable> workQueue;
	//资源锁
    private final ReentrantLock mainLock = new ReentrantLock();
    //工作队列
    private final HashSet<Worker> workers = new HashSet<Worker>();
	//为了支持阻塞
    private final Condition termination = mainLock.newCondition();
	//跟踪线程池最大值
    private int largestPoolSize;
	//完成任务数量
    private long completedTaskCount;
	//线程工厂
    private volatile ThreadFactory threadFactory;
    //拒绝策略
    private volatile RejectedExecutionHandler handler;
    //空闲线程存活时间
    private volatile long keepAliveTime;
   //核心线程是否遵循存活时间标志
    private volatile boolean allowCoreThreadTimeOut;
	//核心线程数量
    private volatile int corePoolSize;
	//最大线程数
    private volatile int maximumPoolSize;
    //默认拒绝策略，直接抛出异常
    private static final RejectedExecutionHandler defaultHandler =
        new AbortPolicy();
	//执行终结器时要使用的上下文
    private final AccessControlContext acc;
	//工作线程封装内部类
    private final class Worker
        extends AbstractQueuedSynchronizer
        implements Runnable
    {
        private static final long serialVersionUID = 6138294804551838833L;
        //工作线程
        final Thread thread;
        //初始任务
        Runnable firstTask;
        //完成任务数量
        volatile long completedTasks;
        //构造方法
        Worker(Runnable firstTask) {
            setState(-1); // 设置状态为未启动
            this.firstTask = firstTask;//初始化任务为当前任务
            this.thread = getThreadFactory().newThread(this);//创建线程
        }

        //执行任务
        public void run() {
            runWorker(this);
        }

        // 返回锁状态
        protected boolean isHeldExclusively() {
            return getState() != 0;
        }
		//尝试获取锁
        protected boolean tryAcquire(int unused) {
            if (compareAndSetState(0, 1)) {
                setExclusiveOwnerThread(Thread.currentThread());
                return true;
            }
            return false;
        }
		//尝试释放锁
        protected boolean tryRelease(int unused) {
            setExclusiveOwnerThread(null);
            setState(0);
            return true;
        }
		//获取锁
        public void lock()        { acquire(1); }
        //尝试获取锁
        public boolean tryLock()  { return tryAcquire(1); }
        //释放锁
        public void unlock()      { release(1); }
        //尝试释放锁
        public boolean isLocked() { return isHeldExclusively(); }
		//如果线程运行中  并未标记中断 进行中断
        void interruptIfStarted() {
            Thread t;
            if (getState() >= 0 && (t = thread) != null && !t.isInterrupted()) {
                try {
                    t.interrupt();
                } catch (SecurityException ignore) {
                }
            }
        }
    }
	//如果要更新的状态小于线程池当前状态  更新线程池状态
    private void advanceRunState(int targetState) {
        for (;;) {
            int c = ctl.get();
            if (runStateAtLeast(c, targetState) ||
                ctl.compareAndSet(c, ctlOf(targetState, workerCountOf(c))))
                break;
        }
    }

    //尝试终止线程池
    final void tryTerminate() {
        for (;;) {
        	// 获取线程池状态
            int c = ctl.get();
            //  判断是否在运行中,如果是直接返回
            if (isRunning(c) ||
            	//状态为SHUTDOWN或STOP 直接返回 队列有任务执行 或者 任务未清理完
                runStateAtLeast(c, TIDYING) ||
                (runStateOf(c) == SHUTDOWN && ! workQueue.isEmpty()))
                return;
            //判断工作线程是否为0 不为0 中断一个工作线程  返回
            if (workerCountOf(c) != 0) { 
                interruptIdleWorkers(ONLY_ONE);
                return;
            }

            final ReentrantLock mainLock = this.mainLock;
            mainLock.lock();
            try {
            	//尝试设置状态为TIDYING
                if (ctl.compareAndSet(c, ctlOf(TIDYING, 0))) {
                    try {
                    	//空方法
                        terminated();
                    } finally {
             			//设置状态为TERMINATED
                        ctl.set(ctlOf(TERMINATED, 0));
                        //唤醒调用了awaitTermination(long timeout, TimeUnit unit)的线程   awaitTermination中调用了
                        termination.signalAll();
                    }
                    return;
                }
            } finally {
                mainLock.unlock();
            }
        }
    }
    //通过安全管理器检查是否有关闭线程权限。
    private void checkShutdownAccess() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkPermission(shutdownPerm);
            final ReentrantLock mainLock = this.mainLock;
            mainLock.lock();
            try {
                for (Worker w : workers)
                    security.checkAccess(w.thread);
            } finally {
                mainLock.unlock();
            }
        }
    }

   ////中断全部工作线程
    private void interruptWorkers() {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            for (Worker w : workers)
                w.interruptIfStarted();
        } finally {
            mainLock.unlock();
        }
    }

    //参数为onlyOne，如果传入true，表示只中断一个线程  否则中断所有空闲线程
    private void interruptIdleWorkers(boolean onlyOne) {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            for (Worker w : workers) {
                Thread t = w.thread;
                ////如果线程未被中断，且获取work的锁成功(说明空闲)，则中断线程
                if (!t.isInterrupted() && w.tryLock()) {
                    try {
                        t.interrupt();
                    } catch (SecurityException ignore) {
                    } finally {
                        w.unlock();
                    }
                }
                if (onlyOne)
                    break;
            }
        } finally {
            mainLock.unlock();
        }
    }

    //中断所有空闲线程
    private void interruptIdleWorkers() {
        interruptIdleWorkers(false);
    }
	//中断工作线程辅助标记。
    private static final boolean ONLY_ONE = true;

   //ScheduledThreadPoolExecutor 使用的策略
    final void reject(Runnable command) {
        handler.rejectedExecution(command, this);
    }

    void onShutdown() {
    }

  	//检查线程池状态是否为RUNNING或SHUTDOWN
    final boolean isRunningOrShutdown(boolean shutdownOK) {
        int rs = runStateOf(ctl.get());
        return rs == RUNNING || (rs == SHUTDOWN && shutdownOK);
    }

    //清空任务队列返回未执行任务
    private List<Runnable> drainQueue() {
        BlockingQueue<Runnable> q = workQueue;
        ArrayList<Runnable> taskList = new ArrayList<Runnable>();
        q.drainTo(taskList);
        if (!q.isEmpty()) {
            for (Runnable r : q.toArray(new Runnable[0])) {
                if (q.remove(r))
                    taskList.add(r);
            }
        }
        return taskList;
    }

 	//增加新的工作线程
    private boolean addWorker(Runnable firstTask, boolean core) {
        retry:
        for (;;) {
            int c = ctl.get();
            int rs = runStateOf(c); 
            // 就是SHUTDOWN  及以上状态 不接受新任务 则不新建工作线程
            // RUNNING 如果队列为空或者firstTask为空 不需要新建工作线程 
            if (rs >= SHUTDOWN &&
                ! (rs == SHUTDOWN &&
                   firstTask == null &&
                   ! workQueue.isEmpty()))
                //则返回false，添加失败
                return false;

            for (;;) {
  				//获取线程数量
                int wc = workerCountOf(c);
                ////判断是否超过线程数量的限制
                if (wc >= CAPACITY ||
                    wc >= (core ? corePoolSize : maximumPoolSize))
                    return false;
                 //未超过限制则尝试把线程数加1，成功跳出循环
                if (compareAndIncrementWorkerCount(c))
                    break retry;
                c = ctl.get();  // Re-read ctl
                //如果期间线程池状态改变  重新进入循环 
                if (runStateOf(c) != rs)
                    continue retry;
            }
        }

        boolean workerStarted = false;
        boolean workerAdded = false;
        Worker w = null;
        try {
        	//创建新的工作线程类对象
            w = new Worker(firstTask);
            //获取线程对象
            final Thread t = w.thread;
            if (t != null) {
            	
                final ReentrantLock mainLock = this.mainLock;、
                //加锁  workers是hashSet类型  线程不安全
                mainLock.lock();
                try {
                    // 获取线程池状态
                    int rs = runStateOf(ctl.get());
					//运行状态为RUNNING  或者 SHUTDOWN 并且 firstTask 为空
                    if (rs < SHUTDOWN ||
                        (rs == SHUTDOWN && firstTask == null)) {
                        //检查线程是否已启动
                        if (t.isAlive()) // precheck that t is startable
                            throw new IllegalThreadStateException();
                        //添加 进工作队列 
                        workers.add(w);
                        //更新线程池最大值
                        int s = workers.size();
                        if (s > largestPoolSize)
                            largestPoolSize = s;
                        workerAdded = true;
                    }
                } finally {
                    mainLock.unlock();
                }
                if (workerAdded) {
                    t.start();
                    workerStarted = true;
                }
            }
        } finally {
            if (! workerStarted)
            	//添加失败则 删除这个 工作对象
                addWorkerFailed(w);
        }
        return workerStarted;
    }

   ////添加失败 删除这个 工作对象
    private void addWorkerFailed(Worker w) {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            if (w != null)
            	//删除
                workers.remove(w);
                //数量减一
            decrementWorkerCount();
            //尝试终止线程池  可能是因为线程池状态变化  导致添加失败  所以尝试终止
            tryTerminate();
        } finally {
            mainLock.unlock();
        }
    }

   //将工作线程从容器中剔除
    private void processWorkerExit(Worker w, boolean completedAbruptly) {
    	// 判断是否是异常情况导致工作线程被回收
        if (completedAbruptly) // If abrupt, then workerCount wasn't adjusted
            // 扣减工作线程总数
            decrementWorkerCount();

        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
        	// 将当前工作线程完成任务的总数加到completedTaskCount上
            completedTaskCount += w.completedTasks;
            workers.remove(w);
        } finally {
            mainLock.unlock();
        }
		// 尝试结束线程池
        tryTerminate();

        int c = ctl.get();
        // 判断当前线程池状态是否为 RUNNING 或者 SHUTDOWN
        if (runStateLessThan(c, STOP)) {
        	//非异常情况导致工作线程被回收
            if (!completedAbruptly) {
            	//最小线程数 
                int min = allowCoreThreadTimeOut ? 0 : corePoolSize;
                if (min == 0 && ! workQueue.isEmpty())
                    min = 1;
                  //如果大于核心数 返回
                if (workerCountOf(c) >= min)
                    return; // replacement not needed
            }
            / //否则创建 工作线程
            addWorker(null, false);
        }
    }
	
   //获取任务
    private Runnable getTask() {
    	 // 超时标志
        boolean timedOut = false; 

        for (;;) {
            int c = ctl.get();
            int rs = runStateOf(c);

           // 停止状态或者任务队列为空
            if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
            	//扣减工作线程总数
                decrementWorkerCount();
                return null;
            }
			//获取线程数量
            int wc = workerCountOf(c);

            // 超时或者超过核心线程数
            boolean timed = allowCoreThreadTimeOut || wc > corePoolSize;
			//超过核心线程池数或者 超时 并且 线程数量大于1 或者 任务队列为空
            if ((wc > maximumPoolSize || (timed && timedOut))
                && (wc > 1 || workQueue.isEmpty())) {
                //线程池工作线程数量减一
                if (compareAndDecrementWorkerCount(c))
                    return null;
                continue;
            }

            try {
            	//获取任务 返回
                Runnable r = timed ?
                    workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) :
                    workQueue.take();
                if (r != null)
                    return r;
                timedOut = true;
            } catch (InterruptedException retry) {
                timedOut = false;
            }
        }
    }

    //执行任务
    final void runWorker(Worker w) {
    	//当前工作线程
        Thread wt = Thread.currentThread();
        //初始化任务
        Runnable task = w.firstTask;
        w.firstTask = null;
        w.unlock(); // allow interrupts
        boolean completedAbruptly = true;
        try {
        	//获取任务
            while (task != null || (task = getTask()) != null) {
                w.lock();
                // 线程池是STOP,TIDYING,TERMINATED状态，中断当前工作线程
                if ((runStateAtLeast(ctl.get(), STOP) ||
                     (Thread.interrupted() &&
                      runStateAtLeast(ctl.get(), STOP))) &&
                    !wt.isInterrupted())
                    wt.interrupt();
                try {
                	//空方法
                    beforeExecute(wt, task);
                    Throwable thrown = null;
                    try {
                    	// 执行任务
                        task.run();
                    } catch (RuntimeException x) {
                        thrown = x; throw x;
                    } catch (Error x) {
                        thrown = x; throw x;
                    } catch (Throwable x) {
                        thrown = x; throw new Error(x);
                    } finally {
                   		 //空方法
                        afterExecute(task, thrown);
                    }
                } finally {
                    task = null;
                    //完成任务+1
                    w.completedTasks++;
                    w.unlock();
                }
            }
            //未出异常   安全执行
            completedAbruptly = false;
        } finally {
        	//将工作线程从容器中剔除
            processWorkerExit(w, completedAbruptly);
        }
    }

    //构造方法 上篇文章写过
	(https://blog.csdn.net/weixin_43001336/article/details/107326880)
    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             Executors.defaultThreadFactory(), defaultHandler);
    }

    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,
                              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,
                              RejectedExecutionHandler handler) {
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
            //java安全管理器
        this.acc = System.getSecurityManager() == null ?
                null :
                AccessController.getContext();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        //转换为纳秒
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }
	//提交任务
    public void execute(Runnable command) {
        if (command == null)
            throw new NullPointerException();
      	//获取线程池标志
        int c = ctl.get();
        //小于核心数  增加工作线程
        if (workerCountOf(c) < corePoolSize) {
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }
       	//RUNNING状态 并且 入队成功
        if (isRunning(c) && workQueue.offer(command)) {
            int recheck = ctl.get();
            //不是RUNNING状态 删除任务 执行拒绝策略 
            if (! isRunning(recheck) && remove(command))
                reject(command);
             //工作队列为0 添加工作队列
            else if (workerCountOf(recheck) == 0)
                addWorker(null, false);
        }
        //创建新线程失败  执行拒绝策略 
        else if (!addWorker(command, false))
            reject(command);
    }

   //关闭线程池
    public void shutdown() {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
        	//检查是否有关闭线程池权限
            checkShutdownAccess();
            //更新线程池状态为SHUTDOWN
            advanceRunState(SHUTDOWN);
            //中断所有空闲工作线程
            interruptIdleWorkers();
            //空方法
            onShutdown(); // hook for ScheduledThreadPoolExecutor
        } finally {
            mainLock.unlock();
        }
        //尝试终止线程池
        tryTerminate();
    }

   //立即 关闭线程池  返回未完成任务
    public List<Runnable> shutdownNow() {
        List<Runnable> tasks;
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
        	//检查是否有关闭线程池权限
            checkShutdownAccess();
            //更新线程状态为STOP
            advanceRunState(STOP);
            //中断所有工作线程
            interruptWorkers();
            //将未完成任务  赋值tasks  并将任务队列清空
            tasks = drainQueue();
        } finally {
            mainLock.unlock();
        }
        //尝试终止线程池
        tryTerminate();
        return tasks;
    }
	//是否SHUTDOWN
    public boolean isShutdown() {
        return ! isRunning(ctl.get());
    }

    //是否可以TERMINATED
    public boolean isTerminating() {
        int c = ctl.get();
        return ! isRunning(c) && runStateLessThan(c, TERMINATED);
    }
	//是否TERMINATED
    public boolean isTerminated() {
        return runStateAtLeast(ctl.get(), TERMINATED);
    }
	//阻塞 unit单位timeout长时间
    public boolean awaitTermination(long timeout, TimeUnit unit)
        throws InterruptedException {
        
        long nanos = unit.toNanos(timeout);
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            for (;;) {
            	//状态是否为TERMINATED
                if (runStateAtLeast(ctl.get(), TERMINATED))
                    return true;
                if (nanos <= 0)
                    return false;
                 //设置等待最大时间  返回真实等待时间
                nanos = termination.awaitNanos(nanos);
            }
        } finally {
            mainLock.unlock();
        }
    }

    //GC执行方法
    protected void finalize() {
        SecurityManager sm = System.getSecurityManager();
        if (sm == null || acc == null) {
            shutdown();
        } else {
            PrivilegedAction<Void> pa = () -> { shutdown(); return null; };
            AccessController.doPrivileged(pa, acc);
        }
    }

    //线程工厂set方法
    public void setThreadFactory(ThreadFactory threadFactory) {
        if (threadFactory == null)
            throw new NullPointerException();
        this.threadFactory = threadFactory;
    }

   //线程工厂get方法
    public ThreadFactory getThreadFactory() {
        return threadFactory;
    }

    //拒绝策略set方法
    public void setRejectedExecutionHandler(RejectedExecutionHandler handler) {
        if (handler == null)
            throw new NullPointerException();
        this.handler = handler;
    }

    //拒绝策略get方法
    public RejectedExecutionHandler getRejectedExecutionHandler() {
        return handler;
    }

    //核心线程数set方法
    public void setCorePoolSize(int corePoolSize) {
        if (corePoolSize < 0)
            throw new IllegalArgumentException();
        int delta = corePoolSize - this.corePoolSize;
        this.corePoolSize = corePoolSize;
        //线程数大于核心数  中断空闲线程
        if (workerCountOf(ctl.get()) > corePoolSize)
            interruptIdleWorkers();
        else if (delta > 0) {
            //增加工作线程  直到  到达新设定的核心数  或者  任务队列为空
            int k = Math.min(delta, workQueue.size());
            while (k-- > 0 && addWorker(null, true)) {
                if (workQueue.isEmpty())
                    break;
            }
        }
    }

    public int getCorePoolSize() {
        return corePoolSize;
    }
	//默认启动一个核心线程
    public boolean prestartCoreThread() {
        return workerCountOf(ctl.get()) < corePoolSize &&
            addWorker(null, true);
    }
	//最少启动一个核心线程  
    void ensurePrestart() {
        int wc = workerCountOf(ctl.get());
        if (wc < corePoolSize)
            addWorker(null, true);
        else if (wc == 0)
            addWorker(null, false);
    }

    //启动所有核心线程等待工作 
    public int prestartAllCoreThreads() {
        int n = 0;
        while (addWorker(null, true))
            ++n;
        return n;
    }
	//返回核心线程否回收标志
    public boolean allowsCoreThreadTimeOut() {
        return allowCoreThreadTimeOut;
    }

   //空闲线程回收方法 
    public void allowCoreThreadTimeOut(boolean value) {
        if (value && keepAliveTime <= 0)
            throw new IllegalArgumentException("Core threads must have nonzero keep alive times");
        if (value != allowCoreThreadTimeOut) {
            allowCoreThreadTimeOut = value;
            if (value)
                interruptIdleWorkers();
        }
    }

    // 设置最大线程数
    public void setMaximumPoolSize(int maximumPoolSize) {
        if (maximumPoolSize <= 0 || maximumPoolSize < corePoolSize)
            throw new IllegalArgumentException();
        this.maximumPoolSize = maximumPoolSize;
        //如果大于最大线程   中断所有核心线程
        if (workerCountOf(ctl.get()) > maximumPoolSize)
            interruptIdleWorkers();
    }

    public int getMaximumPoolSize() {
        return maximumPoolSize;
    }

   //设置存活时间
    public void setKeepAliveTime(long time, TimeUnit unit) {
        if (time < 0)
            throw new IllegalArgumentException();
        if (time == 0 && allowsCoreThreadTimeOut())
            throw new IllegalArgumentException("Core threads must have nonzero keep alive times");
        long keepAliveTime = unit.toNanos(time);
        long delta = keepAliveTime - this.keepAliveTime;
        this.keepAliveTime = keepAliveTime;
        if (delta < 0)
        	//回收空闲线程
            interruptIdleWorkers();
    }

    public long getKeepAliveTime(TimeUnit unit) {
        return unit.convert(keepAliveTime, TimeUnit.NANOSECONDS);
    }

   //返回任务队列
    public BlockingQueue<Runnable> getQueue() {
        return workQueue;
    }

    //删除任务
    public boolean remove(Runnable task) {
        boolean removed = workQueue.remove(task);
        tryTerminate(); //尝试终止线程池
        return removed;
    }

    //清除取消的任务
    public void purge() {
        final BlockingQueue<Runnable> q = workQueue;
        try {
            Iterator<Runnable> it = q.iterator();
            while (it.hasNext()) {
                Runnable r = it.next();
                if (r instanceof Future<?> && ((Future<?>)r).isCancelled())
                    it.remove();
            }
        } catch (ConcurrentModificationException fallThrough) {
  
            for (Object r : q.toArray())
                if (r instanceof Future<?> && ((Future<?>)r).isCancelled())
                    q.remove(r);
        }

        tryTerminate(); // In case SHUTDOWN and now empty
    }


    //返回工作线程数量
    public int getPoolSize() {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            //TIDYING、TERMINATED 返回 0  否则返回 工作线程数量
            return runStateAtLeast(ctl.get(), TIDYING) ? 0
                : workers.size();
        } finally {
            mainLock.unlock();
        }
    }

    //获取工作的线程数   
    public int getActiveCount() {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            int n = 0;
            for (Worker w : workers)
                if (w.isLocked())
                    ++n;
            return n;
        } finally {
            mainLock.unlock();
        }
    }

    //获取线程池曾经历的最大值
    public int getLargestPoolSize() {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            return largestPoolSize;
        } finally {
            mainLock.unlock();
        }
    }

   //获取线程池需要执行的任务数量。
    public long getTaskCount() {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
        	//已经结束线工作程完成的任务数(completedTaskCount) + 还未结束线程工作线程完成的任务数(w.completedTasks)+正在执行的任务数(w.isLocked())+还未执行的任务数(workQueue.size())
            long n = completedTaskCount;
            for (Worker w : workers) {
                n += w.completedTasks;
                if (w.isLocked())
                    ++n;
            }
            return n + workQueue.size();
        } finally {
            mainLock.unlock();
        }
    }

   //获取已完成的任务数量
    public long getCompletedTaskCount() {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
        	//已经结束线工作程完成的任务数(completedTaskCount) + 还未结束线程工作线程完成的任务数(w.completedTasks)
            long n = completedTaskCount;
            for (Worker w : workers)
                n += w.completedTasks;
            return n;
        } finally {
            mainLock.unlock();
        }
    }

    public String toString() {
        long ncompleted;
        int nworkers, nactive;
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            ncompleted = completedTaskCount;
            nactive = 0;
            nworkers = workers.size();
            for (Worker w : workers) {
                ncompleted += w.completedTasks;
                if (w.isLocked())
                    ++nactive;
            }
        } finally {
            mainLock.unlock();
        }
        int c = ctl.get();
        String rs = (runStateLessThan(c, SHUTDOWN) ? "Running" :
                     (runStateAtLeast(c, TERMINATED) ? "Terminated" :
                      "Shutting down"));
        return super.toString() +
            "[" + rs +
            ", pool size = " + nworkers +
            ", active threads = " + nactive +
            ", queued tasks = " + workQueue.size() +
            ", completed tasks = " + ncompleted +
            "]";
    }

 
    protected void beforeExecute(Thread t, Runnable r) { }

    
    protected void afterExecute(Runnable r, Throwable t) { }

   
    protected void terminated() { }

   //内部类拒绝策略   谁提交任务  谁去执行
    public static class CallerRunsPolicy implements RejectedExecutionHandler {
        /**
         * Creates a {@code CallerRunsPolicy}.
         */
        public CallerRunsPolicy() { }

        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
            if (!e.isShutdown()) {
                r.run();
            }
        }
    }

      //内部类拒绝策略   抛出异常
    public static class AbortPolicy implements RejectedExecutionHandler {
        /**
         * Creates an {@code AbortPolicy}.
         */
        public AbortPolicy() { }

        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
            throw new RejectedExecutionException("Task " + r.toString() +
                                                 " rejected from " +
                                                 e.toString());
        }
    }

      //内部类拒绝策略   啥也不干
    public static class DiscardPolicy implements RejectedExecutionHandler {
        /**
         * Creates a {@code DiscardPolicy}.
         */
        public DiscardPolicy() { }

        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
        }
    }

      //内部类拒绝策略   删除任务队列最先入队任务  将当前任务入队
    public static class DiscardOldestPolicy implements RejectedExecutionHandler {
        /**
         * Creates a {@code DiscardOldestPolicy} for the given executor.
         */
        public DiscardOldestPolicy() { }

        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
            if (!e.isShutdown()) {
                e.getQueue().poll();
                e.execute(r);
            }
        }
    }
}

本文地址：https://blog.csdn.net/weixin_43001336/article/details/107372063