@FunctionalInterface
public interface Callable<V> {
    /**
     * Computes a result, or throws an exception if unable to do so.
     *
     * @return computed result
     * @throws Exception if unable to compute a result
     */
    V call() throws Exception;
}

@FunctionalInterface
public interface Runnable {
    /**
     * When an object implementing interface <code>Runnable</code> is used
     * to create a thread, starting the thread causes the object's
     * <code>run</code> method to be called in that separately executing
     * thread.
     * <p>
     * The general contract of the method <code>run</code> is that it may
     * take any action whatsoever.
     *
     * @see     java.lang.Thread#run()
     */
    public abstract void run();
}

<T> Future<T> submit(Callable<T> task);
<T> Future<T> submit(Runnable task, T result);
Future<?> submit(Runnable task);

public interface Future<V> {
    boolean cancel(boolean mayInterruptIfRunning);
    boolean isCancelled();
    boolean isDone();
    V get() throws InterruptedException, ExecutionException;
    V get(long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException;
}

public class FutureTask<V> implements RunnableFuture<V> {
...
}

public interface RunnableFuture<V> extends Runnable, Future<V> {
    /**
     * Sets this Future to the result of its computation
     * unless it has been cancelled.
     */
    void run();
}

import java.util.concurrent.*;
public class AsynDemo {
    public static void main(String[] args) {
        // 初始化線程池
        ExecutorService threadPool = Executors.newFixedThreadPool(5);
        // 初始化線程任務(wù)
        MyTask myTask = new MyTask(5);
        // 向線程池遞交線程任務(wù)
        Future<Integer> result = threadPool.submit(myTask);
        // 主線程休眠2秒，模擬主線程在做其他的事情
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        // 主線程獲取異步任務(wù)的執(zhí)行結(jié)果
        try {
            System.out.println("異步線程任務(wù)執(zhí)行結(jié)果 " + result.get());
            System.out.println("檢查異步線程任務(wù)是否執(zhí)行完畢 " + result.isDone());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
    }
    // 靜態(tài)內(nèi)部類，實現(xiàn)Callable接口的任務(wù)類
    static class MyTask implements Callable<Integer> {
        private int num;
        public MyTask(int num) {
            this.num = num;
        }
        @Override
        public Integer call() throws Exception {
            for (int i = 1; i < 10; ++i) {
                this.num *= i;
            }
            return this.num;
        }
    }
}

import java.util.concurrent.*;
public class FutureTaskDemo {
    public static void main(String[] args) {
        // 初始化線程池
        ExecutorService threadPool = Executors.newFixedThreadPool(5);
        // 初始化MyTask實例
        MyTask myTask = new MyTask(5);
        // 用MyTask的實例對象初始化一個FutureTask對象
        FutureTask<Integer> myFutureTask = new FutureTask<>(myTask);
        // 向線程池遞交線程任務(wù)
        threadPool.submit(myFutureTask);
        // 關(guān)閉線程池
        threadPool.shutdown();
        // 主線程休眠2秒，模擬主線程在做其他的事情
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        // 主線程獲取異步任務(wù)的執(zhí)行結(jié)果
        try {
            System.out.println("異步線程任務(wù)執(zhí)行結(jié)果 " + myFutureTask.get());
            System.out.println("檢查異步線程任務(wù)是否執(zhí)行完畢 " + myFutureTask.isDone());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
    }
    // 靜態(tài)內(nèi)部類，實現(xiàn)Callable接口的任務(wù)類
    static class MyTask implements Callable<Integer> {
        private int num;
        public MyTask(int num) {
            this.num = num;
        }
        @Override
        public Integer call() throws Exception {
            System.out.println(Thread.currentThread().getName() + " 正在執(zhí)行異步任務(wù)");
            for (int i = 1; i < 10; ++i) {
                this.num *= i;
            }
            return this.num;
        }
    }
}

//內(nèi)部持有的callable任務(wù)，運(yùn)行完畢后置空
private Callable<V> callable;
//從get()中返回的結(jié)果或拋出的異常
private Object outcome; // non-volatile, protected by state reads/writes
//運(yùn)行callable的線程
private volatile Thread runner;
//使用Treiber棧保存等待線程
private volatile WaitNode waiters;
//任務(wù)狀態(tài)
private volatile int state;
private static final int NEW          = 0;
private static final int COMPLETING   = 1;
private static final int NORMAL       = 2;
private static final int EXCEPTIONAL  = 3;
private static final int CANCELLED    = 4;
private static final int INTERRUPTING = 5;
private static final int INTERRUPTED  = 6;

public FutureTask(Callable<V> callable) {
    if (callable == null)
        throw new NullPointerException();
    this.callable = callable;
    this.state = NEW;       // ensure visibility of callable
}

public FutureTask(Runnable runnable, V result) {
    this.callable = Executors.callable(runnable, result);
    this.state = NEW;       // ensure visibility of callable
}

public static <T> Callable<T> callable(Runnable task, T result) {
    if (task == null)
       throw new NullPointerException();
    return new RunnableAdapter<T>(task, result);
}

static final class RunnableAdapter<T> implements Callable<T> {
    final Runnable task;
    final T result;
    RunnableAdapter(Runnable task, T result) {
        this.task = task;
        this.result = result;
    }
    public T call() {
        task.run();
        return result;
    }
}

public void run() {
    //新建任務(wù)，CAS替換runner為當(dāng)前線程
    if (state != NEW ||
        !UNSAFE.compareAndSwapObject(this, runnerOffset,
                                     null, Thread.currentThread()))
        return;
    try {
        Callable<V> c = callable;
        if (c != null && state == NEW) {
            V result;
            boolean ran;
            try {
                result = c.call();
                ran = true;
            } catch (Throwable ex) {
                result = null;
                ran = false;
                setException(ex);
            }
            if (ran)
                set(result);//設(shè)置執(zhí)行結(jié)果
        }
    } finally {
        // runner must be non-null until state is settled to
        // prevent concurrent calls to run()
        runner = null;
        // state must be re-read after nulling runner to prevent
        // leaked interrupts
        int s = state;
        if (s >= INTERRUPTING)
            handlePossibleCancellationInterrupt(s);//處理中斷邏輯
    }
}

protected void set(V v) {
    if (UNSAFE.compareAndSwapInt(this, stateOffset, NEW, COMPLETING)) {
        outcome = v;
        UNSAFE.putOrderedInt(this, stateOffset, NORMAL); // final state
        finishCompletion();//執(zhí)行完畢，喚醒等待線程
    }
}

private void finishCompletion() {
    // assert state > COMPLETING;
    for (WaitNode q; (q = waiters) != null;) {
        if (UNSAFE.compareAndSwapObject(this, waitersOffset, q, null)) {//移除等待線程
            for (;;) {//自旋遍歷等待線程
                Thread t = q.thread;
                if (t != null) {
                    q.thread = null;
                    LockSupport.unpark(t);//喚醒等待線程
                }
                WaitNode next = q.next;
                if (next == null)
                    break;
                q.next = null; // unlink to help gc
                q = next;
            }
            break;
        }
    }
    //任務(wù)完成后調(diào)用函數(shù)，自定義擴(kuò)展
    done();
    callable = null;        // to reduce footprint
}

???????
private void handlePossibleCancellationInterrupt(int s) {
    //在中斷者中斷線程之前可能會延遲，所以我們只需要讓出CPU時間片自旋等待
    if (s == INTERRUPTING)
        while (state == INTERRUPTING)
            Thread.yield(); // wait out pending interrupt
}

//獲取執(zhí)行結(jié)果
public V get() throws InterruptedException, ExecutionException {
    int s = state;
    if (s <= COMPLETING)
        s = awaitDone(false, 0L);
    return report(s);
}

//返回執(zhí)行結(jié)果或拋出異常
private V report(int s) throws ExecutionException {
    Object x = outcome;
    if (s == NORMAL)
        return (V)x;
    if (s >= CANCELLED)
        throw new CancellationException();
    throw new ExecutionException((Throwable)x);
}

private int awaitDone(boolean timed, long nanos)
    throws InterruptedException {
    final long deadline = timed ? System.nanoTime() + nanos : 0L;
    WaitNode q = null;
    boolean queued = false;
    for (;;) {//自旋
        if (Thread.interrupted()) {//獲取并清除中斷狀態(tài)
            removeWaiter(q);//移除等待WaitNode
            throw new InterruptedException();
        }
        int s = state;
        if (s > COMPLETING) {
            if (q != null)
                q.thread = null;//置空等待節(jié)點的線程
            return s;
        }
        else if (s == COMPLETING) // cannot time out yet
            Thread.yield();
        else if (q == null)
            q = new WaitNode();
        else if (!queued)
            //CAS修改waiter
            queued = UNSAFE.compareAndSwapObject(this, waitersOffset,
                                                 q.next = waiters, q);
        else if (timed) {
            nanos = deadline - System.nanoTime();
            if (nanos <= 0L) {
                removeWaiter(q);//超時，移除等待節(jié)點
                return state;
            }
            LockSupport.parkNanos(this, nanos);//阻塞當(dāng)前線程
        }
        else
            LockSupport.park(this);//阻塞當(dāng)前線程
    }
}

private void removeWaiter(WaitNode node) {
    if (node != null) {
        node.thread = null;//首先置空線程
        retry:
        for (;;) {          // restart on removeWaiter race
            //依次遍歷查找
            for (WaitNode pred = null, q = waiters, s; q != null; q = s) {
                s = q.next;
                if (q.thread != null)
                    pred = q;
                else if (pred != null) {
                    pred.next = s;
                    if (pred.thread == null) // check for race
                        continue retry;
                }
                else if (!UNSAFE.compareAndSwapObject(this, waitersOffset,q, s)) //cas替換
                    continue retry;
            }
            break;
        }
    }
}

public boolean cancel(boolean mayInterruptIfRunning) {
    //如果當(dāng)前Future狀態(tài)為NEW，根據(jù)參數(shù)修改Future狀態(tài)為INTERRUPTING或CANCELLED
    if (!(state == NEW &&
          UNSAFE.compareAndSwapInt(this, stateOffset, NEW,
              mayInterruptIfRunning ? INTERRUPTING : CANCELLED)))
        return false;
    try {    // in case call to interrupt throws exception
        if (mayInterruptIfRunning) {//可以在運(yùn)行時中斷
            try {
                Thread t = runner;
                if (t != null)
                    t.interrupt();
            } finally { // final state
                UNSAFE.putOrderedInt(this, stateOffset, INTERRUPTED);
            }
        }
    } finally {
        finishCompletion();//移除并喚醒所有等待線程
    }
    return true;
}