自定义FutureTask实现

public class ThreadTest {public static void main(String[] args) throws Exception {Callable<String> myCallable = new MyCallableThread();
FutureTask<String> futureTask = new FutureTask<>(myCallable);
Thread myCallableThread = new Thread(futureTask);
myCallableThread.setName("MyThread-implements-Callable-test");
myCallableThread.start();
System.out.println("Run by Thread:" + futureTask.get());//通过线程池执行
ExecutorService executorService = Executors.newCachedThreadPool();
executorService.submit(futureTask);
executorService.shutdown();
System.out.println("Run by ExecutorService:" + futureTask.get());
}
}class MyCallableThread implements Callable<String> {@Override
public String call() throws Exception {
return Thread.currentThread().getName();
}
}

/**
* 1. 泛型定义
* 2. 构造方法 callable
* 3. 实现了runnable
* 4. get方法返回callable执行结果
* 5. get方法有阻塞的效果（未执行结束的话）
*/
public class MyFutureTask<T> implements Runnable {// 程序执行的结果
private T result;// 要执行的任务
private Callable<T> callable;// 任务运行的状态
private volatile int state = NEW;// 任务运行的状态值
private static final int NEW = 0;
private static final int RUNNING = 1;
private static final int FINISHED = 2;// 获取结果的线程等待队列
LinkedBlockingQueue<Thread> waiters = new LinkedBlockingQueue<>(100);// 执行当前FutureTask的线程，用CAS进行争抢
AtomicReference<Thread> runner = new AtomicReference<>();public MyFutureTask(Callable<T> task) {
this.callable = task;
}@Override
public void run() {
// 判断当前对象的状态，如果是New且抢锁成功就执行
if (state != NEW || !runner.compareAndSet(null, Thread.currentThread())) return;
state = RUNNING;
try {
result = callable.call();
} catch (Exception e) {
e.printStackTrace();
} finally {
state = FINISHED;
}// 方法执行完，唤醒所有线程
while (true) {
Thread waiterThread = waiters.poll();
if (waiterThread == null) break;
LockSupport.unpark(waiterThread);
}
}public T get() {
// 如果状态不是FINISHED，则进入等待队列
if (state != FINISHED) {
waiters.offer(Thread.currentThread());
}
while (state != FINISHED) {
LockSupport.park();
}
return result;
}
}// MyFutureTask 测试
public class FutureTaskTest {
public static void main(String[] args) {Callable<String> myCallable = new MyCallableThread();
MyFutureTask<String> futureTask = new MyFutureTask<>(myCallable);
Thread myCallableThread = new Thread(futureTask);
myCallableThread.setName("MyFutureTask-test");
myCallableThread.start();
System.out.println("Run by Thread:" + futureTask.get());
}
}class MyCallableThread implements Callable<String> {@Override
public String call() throws Exception {
return Thread.currentThread().getName();
}
}