java ThreadPoolExecutor线程池内部处理流程解析

// 设置线程池时指定核心线程数、最大线程数、线程存活时间及等待队列。
// 线程创建工厂和拒绝策略使用默认的（AbortPolicy）
public ThreadPoolExecutor(int corePoolSize,
                          int maximumPoolSize,
                          long keepAliveTime,
                          TimeUnit unit,
                          BlockingQueue<Runnable> workQueue) {
    this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
         Executors.defaultThreadFactory(), defaultHandler);
}
// 设置线程池时指定核心线程数、最大线程数、线程存活时间、等待队列及线程创建工厂 
// 拒绝策略使用默认的（AbortPolicy）
public ThreadPoolExecutor(int corePoolSize,
                          int maximumPoolSize,
                          long keepAliveTime,
                          TimeUnit unit,
                          BlockingQueue<Runnable> workQueue,
                          ThreadFactory threadFactory) {
    this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
         threadFactory, defaultHandler);
}
// 设置线程池时指定核心线程数、最大线程数、线程存活时间、等待队列及拒绝策略
// 线程创建工厂使用默认的
public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              RejectedExecutionHandler handler) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             Executors.defaultThreadFactory(), handler);
   }
// 设置线程池时指定核心线程数、最大线程数、线程存活时间、等待队列、线程创建工厂及拒绝策略
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;
    }

 public void execute(Runnable command) {
        // 判断提交的任务command是否为null，若是null，则抛出空指针异常；
        if (command == null)
            throw new NullPointerException();
        // 获取线程池中当前线程数
        int c = ctl.get();
        // 如果线程池中当前线程数小于核心池大小，进入if语句块
        if (workerCountOf(c) < corePoolSize) {
            // 如果以给定的命令启动一个核心线程执行任务成功，直接返回
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }
        // 如果当前线程池处于RUNNING状态，则将任务放入任务缓存队列
        if (isRunning(c) && workQueue.offer(command)) {
            int recheck = ctl.get();
            // 如果线程池不处于运行状态并且移除刚加入的任务成功则执行拒绝策略
            if (! isRunning(recheck) && remove(command))
                reject(command);
            // 如果当前线程数为0，则在线程池里增加一个线程，保证队列里的任务不会没有线程执行
            else if (workerCountOf(recheck) == 0)
                addWorker(null, false);
        } 
        // 尝试启动核心线程之外的线程，如果不满足，则执行对应的拒绝策略
        else if (!addWorker(command, false))
            reject(command);
    }

private boolean addWorker(Runnable firstTask, boolean core) {
        retry:
        for (;;) {
            int c = ctl.get();
            int rs = runStateOf(c);
            // 如果线程池状态大于SHUTDOWN或者线程池状态等于SHUTDOWN，firstTask不等于null
            // 或者线程池状态等于SHUTDOWN,任务队列等于空时，直接返回false结束。
            if (rs >= SHUTDOWN &&
                ! (rs == SHUTDOWN &&
                   firstTask == null &&
                   ! workQueue.isEmpty()))
                return false;
            for (;;) {
                int wc = workerCountOf(c);
                // 如果线程数量大于等于最大数量或者大于等于上限
                //（入参core传true,取核心线程数，否则取最大线程数），直接返回false结束。
                if (wc >= CAPACITY ||
                    wc >= (core ? corePoolSize : maximumPoolSize))
                    return false
                // CAS操作给工作线程数加1，成功则跳到retry处，不再进入循环。
                if (compareAndIncrementWorkerCount(c))
                    break retry;
                c = ctl.get();  // Re-read ctl
                // 如果线程池状态与刚进入时不一致，则跳到retry处，再次进入循环
                if (runStateOf(c) != rs)
                    continue retry;
                // else CAS failed due to workerCount change; retry inner loop
            }
        }
        boolean workerStarted = false;
        boolean workerAdded = false;
        Worker w = null;
        try {
            // 新建一个线程
            w = new Worker(firstTask);
            final Thread t = w.thread;
            if (t != null) {
                final ReentrantLock mainLock = this.mainLock;
                mainLock.lock();
                try {
                    int rs = runStateOf(ctl.get());
                    // 如果线程池状态在SHUTDOWN之前或者
                    // 线程池状态等于SHUTDOWN并且firstTask等于null时，进入处理。
                    if (rs < SHUTDOWN ||
                        (rs == SHUTDOWN && firstTask == null)) {
                        // 如果要执行的线程正在运行，则抛异常
                        if (t.isAlive()) // precheck that t is startable
                            throw new IllegalThreadStateException();
                        workers.add(w);
                        int s = workers.size();
                        if (s > largestPoolSize)
                            largestPoolSize = s;
                        workerAdded = true;
                    }
                } finally {
                    mainLock.unlock();
                }
                if (workerAdded) {
                    // 启动线程
                    t.start();
                    workerStarted = true;
                }
            }
        } finally {
            // 如果线程添加失败，则将新增的对应信息删除
            if (! workerStarted)
                addWorkerFailed(w);
        }
        return workerStarted;
    }

public void run() {
            runWorker(this);
        }
final void runWorker(Worker w) {
        Thread wt = Thread.currentThread();
        Runnable task = w.firstTask;
        w.firstTask = null;
        w.unlock(); // allow interrupts
        boolean completedAbruptly = true;
        try {
            // 如果任务不为空或者新获取到的任务不为空
            while (task != null || (task = getTask()) != null) {
                w.lock();
                // 当线程池状态，大于等于 STOP 时，保证工作线程都有中断标志。
                // 当线程池状态，小于STOP时，保证工作线程都没有中断标志。
                if ((runStateAtLeast(ctl.get(), STOP) ||
                     (Thread.interrupted() &&
                      runStateAtLeast(ctl.get(), STOP))) &&
                    !wt.isInterrupted())
                    wt.interrupt();
                try {
                    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 {
                        afterExecute(task, thrown);
                    }
                } finally {
                    task = null;
                    w.completedTasks++;
                    w.unlock();
                }
            }
            completedAbruptly = false;
        } finally {
            processWorkerExit(w, completedAbruptly);
        }
    }