public class CustomThreadPoolDemo  {
    public static void main(String[] args) {
        // 創(chuàng)建線程池，大小為3，最大線程數(shù)為6，空閑線程存活時(shí)間為5秒，使用自定義線程工廠和拒絕策略
        ThreadPoolExecutor executor = new ThreadPoolExecutor(3, 6, 5, TimeUnit.SECONDS,
                new LinkedBlockingQueue<>(10), new CustomThreadFactory(), new CustomRejectedExecutionHandler());
        // 提交10個(gè)任務(wù)
        for (int i = 0; i < 10; i++) {
            executor.submit(new Task(i));
        }
        // 關(guān)閉線程池
        executor.shutdown();
    }
    static class Task implements Runnable {
        private int taskId;
        public Task(int taskId) {
            this.taskId = taskId;
        }
        @Override
        public void run() {
            System.out.println("Task " + taskId + " is running in thread " + Thread.currentThread().getName());
            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("Task " + taskId + " is done.");
        }
    }
    static class CustomThreadFactory implements java.util.concurrent.ThreadFactory {
        private int count = 1;
        @Override
        public Thread newThread(Runnable r) {
            Thread t = new Thread(r);
            t.setName("CustomThreadPool-" + count++);
            return t;
        }
    }
    static class CustomRejectedExecutionHandler implements java.util.concurrent.RejectedExecutionHandler {
        @Override
        public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
            System.out.println("Task " + ((Task) r).taskId + " is rejected.");
        }
    }
}

Future<?> submit(Runnable task) 
void execute(Runnable command)

public Future<?> submit(Runnable task) {
    if (task == null) throw new NullPointerException();
    RunnableFuture<Void> ftask = newTaskFor(task, null);
    execute(ftask);
    return ftask;
}

private final AtomicInteger ctl

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;

public void execute(Runnable command) {
    if (command == null)
        throw new NullPointerException();
    //ctl初始值是ctlOf(RUNNING, 0)，表示線程池處于運(yùn)行中，工作線程數(shù)為0
    int c = ctl.get();
    //判斷工作線程是否小于核心線程數(shù)
    if (workerCountOf(c) < corePoolSize) {
        //小于核心線程要新增工作線程
        if (addWorker(command, true))
            return;
        //新增失敗重新獲取一次ctl
        c = ctl.get();
    }
    //線程池是否處于Running狀態(tài) && 入隊(duì)是否成功
    if (isRunning(c) && workQueue.offer(command)) {//入隊(duì)成功
        //重新獲取ctl
        int recheck = ctl.get();
        //如果線程池不是Running狀態(tài)就需要移除掉這個(gè)任務(wù)
        if (! isRunning(recheck) && remove(command))
            //觸發(fā)拒絕策略
            reject(command);
             //工作線程為0時(shí)要去創(chuàng)建新的工作線程
        else if (workerCountOf(recheck) == 0)
            addWorker(null, false);
    }
    // 如果線程池狀態(tài)不是RUNNING，或者線程池狀態(tài)是RUNNING但是隊(duì)列滿(mǎn)了，則去添加一個(gè)非核心工作線程。false表示非核心線程
    else if (!addWorker(command, false))
        reject(command);
}

//core:true核心線程 false非核心線程
private boolean addWorker(Runnable firstTask, boolean core) {
    retry:
    for (;;) {
        //獲取ctl值
        int c = ctl.get();
        //獲取高3位
        int rs = runStateOf(c);
        // 線程池如果是SHUTDOWN狀態(tài)并且隊(duì)列非空則創(chuàng)建線程，如果隊(duì)列為空則不創(chuàng)建線程
        // 線程池如果是STOP狀態(tài)則直接不創(chuàng)建線程
        if (rs >= SHUTDOWN &&
            ! (rs == SHUTDOWN &&
               firstTask == null &&
               ! workQueue.isEmpty()))
            return false;
        for (;;) {
            //獲取工作線程數(shù)
            int wc = workerCountOf(c);
            //工作線程數(shù)超過(guò)規(guī)定數(shù)量則不創(chuàng)建線程
            if (wc >= CAPACITY ||
                wc >= (core ? corePoolSize : maximumPoolSize))
                return false;
            //修改工作線程
            if (compareAndIncrementWorkerCount(c))
               //成功則退出 retry這個(gè)循環(huán)
                break retry;
            //CAS失敗說(shuō)明有其他線程也在增加工作線程數(shù)量，此時(shí)重新獲取ctl值
            c = ctl.get();  // Re-read ctl
            //如果發(fā)現(xiàn)線程池的狀態(tài)發(fā)生了變化，則繼續(xù)回到retry，重新判斷線程池的狀態(tài)是不是SHUTDOWN或STOP
            // 如果狀態(tài)沒(méi)有變化，則繼續(xù)利用cas來(lái)增加工作線程數(shù)，直到cas成功
            if (runStateOf(c) != rs)
                continue retry;
            // else CAS failed due to workerCount change; retry inner loop
        }
    }
    //到了這里說(shuō)明ctl新增成功
    boolean workerStarted = false;
    boolean workerAdded = false;
    Worker w = null;
    try {
        //Worker實(shí)現(xiàn)了Runnable接口 在構(gòu)造一個(gè)Worker對(duì)象時(shí)，就會(huì)利用ThreadFactory新建一個(gè)線程
        w = new Worker(firstTask);
        //拿出線程對(duì)象此時(shí)線程還沒(méi)有start啟動(dòng)
        final Thread t = w.thread;
        if (t != null) {
            final ReentrantLock mainLock = this.mainLock;
            mainLock.lock();
            try {
                // 獲取高三位
                int rs = runStateOf(ctl.get());
                // 如果線程池的狀態(tài)是RUNNING
                // 或者線程池的狀態(tài)變成了SHUTDOWN，但是當(dāng)前線程沒(méi)有自己的第一個(gè)任務(wù)，那就表示當(dāng)前調(diào)用addWorker方法是為了從隊(duì)列中獲取任務(wù)來(lái)執(zhí)行
                // 正常情況下線程池的狀態(tài)如果是SHUTDOWN，是不能創(chuàng)建新的工作線程的，但是隊(duì)列中如果有任務(wù)，那就是上面說(shuō)的特例情況
                if (rs < SHUTDOWN ||
                    (rs == SHUTDOWN && firstTask == null)) {
                    // 如果Worker對(duì)象對(duì)應(yīng)的線程已經(jīng)在運(yùn)行了，那就有問(wèn)題，直接拋異常
                    if (t.isAlive()) // precheck that t is startable
                        throw new IllegalThreadStateException();
                    // workers用來(lái)記錄當(dāng)前線程池中工作線程，調(diào)用線程池的shutdown方法時(shí)會(huì)遍歷worker對(duì)象中斷對(duì)應(yīng)線程
                    workers.add(w);
                    int s = workers.size();
                    // largestPoolSize用來(lái)跟蹤線程池在運(yùn)行過(guò)程中工作線程數(shù)的峰值
                    if (s > largestPoolSize)
                        largestPoolSize = s;
                    workerAdded = true;
                }
            } finally {
                mainLock.unlock();
            }
            //啟動(dòng)線程
            if (workerAdded) {
                t.start();
                workerStarted = true;
            }
        }
    } finally {
    // 在上述過(guò)程中如果拋了異常，需要從works中移除所添加的work，并且還要修改ctl，工作線程數(shù)-1，表示新建工作線程失敗
        if (! workerStarted)
            addWorkerFailed(w);
    }
    return workerStarted;
}

Worker(Runnable firstTask) {
    setState(-1); // inhibit interrupts until runWorker
    this.firstTask = firstTask;
    this.thread = getThreadFactory().newThread(this);
}
/** Delegates main run loop to outer runWorker  */
public void run() {
    runWorker(this);
}

final void runWorker(Worker w) {
    //獲取當(dāng)前工作線程
    Thread wt = Thread.currentThread();
    //獲取第一個(gè)任務(wù)
    Runnable task = w.firstTask;
    //置空
    w.firstTask = null;
    w.unlock(); // allow interrupts
    boolean completedAbruptly = true;
    try {
        //判斷當(dāng)前第一個(gè)任務(wù)是否為空，為空的話(huà)從阻塞隊(duì)列獲取一個(gè)任務(wù)，阻塞隊(duì)列也為空就會(huì)阻塞在getTask()方法中
        //也不會(huì)一直阻塞下去，keepAliveTime超時(shí)后還沒(méi)有獲取到任務(wù)就會(huì)返回null，退出循環(huán)，這個(gè)線程也就是中止了
        while (task != null || (task = getTask()) != null) {
            w.lock();
            //線程池狀態(tài)為STOP，則要中斷自己，但是如果發(fā)現(xiàn)中斷標(biāo)記為true，那是不對(duì)的，因?yàn)榫€程池狀態(tài)不是STOP，工作線程仍然是要正常工作的，不能中斷掉，算是SHUTDOWN，也要等任務(wù)都執(zhí)行完之后，線程才結(jié)束，而目前線程還在執(zhí)行任務(wù)的過(guò)程中，不能中斷
            if ((runStateAtLeast(ctl.get(), STOP) ||
                 (Thread.interrupted() &&
                  runStateAtLeast(ctl.get(), STOP))) &&
                !wt.isInterrupted())
                wt.interrupt();
            try {
                //空方法給自定義線程池實(shí)現(xiàn)
                beforeExecute(wt, task);
                Throwable thrown = null;
                try {
                    //執(zhí)行任務(wù)
                    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 {
                    //空方法給自定義線程池實(shí)現(xiàn)
                    afterExecute(task, thrown);
                }
            } finally {
                task = null;
                w.completedTasks++;
                w.unlock();
            }
        }
        //正常退出了while循環(huán)
        // completedAbruptly=false，表示線程正常退出
        completedAbruptly = false;
    } finally {
        //如果線程正常退出這個(gè)線程會(huì)自然死亡
        //但是如果是由于執(zhí)行任務(wù)的時(shí)候拋了異常，那么這個(gè)線程不應(yīng)該直接結(jié)束，而應(yīng)該繼續(xù)從隊(duì)列中獲取下一個(gè)任務(wù)
        processWorkerExit(w, completedAbruptly);
    }
}

private void processWorkerExit(Worker w, boolean completedAbruptly) {
   //如果completedAbruptly為true，表示是執(zhí)行任務(wù)的時(shí)候拋了異常，那就修改ctl，工作線程數(shù)-1
    if (completedAbruptly) // If abrupt, then workerCount wasn't adjusted
        decrementWorkerCount();
    final ReentrantLock mainLock = this.mainLock;
    mainLock.lock();
    try {
        completedTaskCount += w.completedTasks;
        // 將當(dāng)前Work對(duì)象從workers中移除
        workers.remove(w);
    } finally {
        mainLock.unlock();
    }
    // 因?yàn)楫?dāng)前是處理線程退出流程中，所以要嘗試去修改線程池的狀態(tài)為T(mén)INDYING
    tryTerminate();
    //獲取當(dāng)前ctl值
    int c = ctl.get();
    // 如果線程池的狀態(tài)為RUNNING或者SHUTDOWN，則可能要替補(bǔ)一個(gè)線程
    if (runStateLessThan(c, STOP)) {
        // completedAbruptly為false，表示線程是正常要退出了，則看是否需要保留線程
        if (!completedAbruptly) {
        // 如果allowCoreThreadTimeOut為true，但是阻塞隊(duì)列中還有任務(wù)，那就至少得保留一個(gè)工作線程來(lái)處理阻塞隊(duì)列中的任務(wù)
        // 如果allowCoreThreadTimeOut為false，那min就是corePoolSize，表示至少得保留corePoolSize個(gè)工作線程活著
            int min = allowCoreThreadTimeOut ? 0 : corePoolSize;
            if (min == 0 && ! workQueue.isEmpty())
                min = 1;
            // 如果當(dāng)前工作線程數(shù)大于等于min，則表示符合所需要保留的最小線程數(shù)，那就直接return，不會(huì)調(diào)用下面的addWorker方法新開(kāi)一個(gè)工作線程了
            if (workerCountOf(c) >= min)
                return; // replacement not needed
        }
        //新開(kāi)工作線程
        addWorker(null, false);
    }
}

private Runnable getTask() {
    boolean timedOut = false; // Did the last poll() time out?
    for (;;) {
        int c = ctl.get();
        int rs = runStateOf(c);
        // 如果線程池狀態(tài)是STOP，表示當(dāng)前線程不需要處理任務(wù)了，那就修改ctl工作線程數(shù)-1
        // 如果線程池狀態(tài)是SHUTDOWN，但是阻塞隊(duì)列中為空，表示當(dāng)前任務(wù)沒(méi)有任務(wù)要處理了，那就修改ctl工作線程數(shù)-1
        // return null表示當(dāng)前線程無(wú)需處理任務(wù)，線程退出
        if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
            decrementWorkerCount();
            return null;
        }
        //當(dāng)前工作線程數(shù)
        int wc = workerCountOf(c);
        // 用來(lái)判斷當(dāng)前線程是無(wú)限阻塞還是超時(shí)阻塞，如果一個(gè)線程超時(shí)阻塞，那么一旦超時(shí)了，那么這個(gè)線程最終就會(huì)退出
        // 如果是無(wú)限阻塞，那除非被中斷了，不然這個(gè)線程就一直等著獲取隊(duì)列中的任務(wù)
        // allowCoreThreadTimeOut為true，表示線程池中的所有線程都可以被回收掉，則當(dāng)前線程應(yīng)該直接使用超時(shí)阻塞，一旦超時(shí)就回收
        // allowCoreThreadTimeOut為false，則要看當(dāng)前工作線程數(shù)是否超過(guò)了corePoolSize，如果超過(guò)了，則表示超過(guò)部分的線程要用超時(shí)阻塞，一旦超時(shí)就回收
        boolean timed = allowCoreThreadTimeOut || wc > corePoolSize;
        // 如果工作線程數(shù)超過(guò)了工作線程的最大限制或者線程超時(shí)了，則要修改ctl，工作線程數(shù)減1，并且return null
        // return null就會(huì)導(dǎo)致外層的while循環(huán)退出，從而導(dǎo)致線程直接運(yùn)行結(jié)束
        // 直播課程里會(huì)細(xì)講timed && timedOut
        if ((wc > maximumPoolSize || (timed && timedOut))
            && (wc > 1 || workQueue.isEmpty())) {
            if (compareAndDecrementWorkerCount(c))
                return null;
            continue;
        }
        try {
            // 要么超時(shí)阻塞，要么無(wú)限阻塞
            Runnable r = timed ?
                workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) :
                workQueue.take();
            // 表示沒(méi)有超時(shí)，在阻塞期間獲取到了任務(wù)
            if (r != null)
                return r;
            // 超時(shí)了，重新進(jìn)入循環(huán)，上面的代碼會(huì)判斷出來(lái)當(dāng)前線程阻塞超時(shí)了，最后return null，線程會(huì)運(yùn)行結(jié)束
            timedOut = true;
        } catch (InterruptedException retry) {
        // 如果線程池的狀態(tài)變成了STOP或者SHUTDOWN，最終也會(huì)return null，線程會(huì)運(yùn)行結(jié)束
        // 但是如果線程池的狀態(tài)仍然是RUNNING，那當(dāng)前線程會(huì)繼續(xù)從隊(duì)列中去獲取任務(wù)，表示忽略了本次中斷
        // 只有通過(guò)調(diào)用線程池的shutdown方法或shutdownNow方法才能真正中斷線程池中的線程
            timedOut = false;
        }
    }
}

public void shutdown() {
    final ReentrantLock mainLock = this.mainLock;
    mainLock.lock();
    try {
        checkShutdownAccess();
        // 修改ctl，將線程池狀態(tài)改為SHUTDOWN
        advanceRunState(SHUTDOWN);
        // 中斷工作線程
        interruptIdleWorkers();
        // 空方法，給子類(lèi)擴(kuò)展使用
        onShutdown(); // hook for ScheduledThreadPoolExecutor
    } finally {
        mainLock.unlock();
    }
    tryTerminate();
}

private void interruptIdleWorkers(boolean onlyOne) {
    final ReentrantLock mainLock = this.mainLock;
    mainLock.lock();
    try {
        // 遍歷所有正在工作的線程，要么在執(zhí)行任務(wù)，要么在阻塞等待任務(wù)
        for (Worker w : workers) {
            Thread t = w.thread;
            // 如果線程沒(méi)有被中斷，并且能夠拿到鎖，就中斷線程
            // Worker在執(zhí)行任務(wù)時(shí)會(huì)先加鎖，執(zhí)行完任務(wù)之后會(huì)釋放鎖
            // 所以只要這里拿到了鎖，就表示線程空出來(lái)了，可以中斷了
            if (!t.isInterrupted() && w.tryLock()) {
                try {
                    t.interrupt();
                } catch (SecurityException ignore) {
                } finally {
                    w.unlock();
                }
            }
            if (onlyOne)
                break;
        }
    } finally {
        mainLock.unlock();
    }
}