Future与Executor模型

歪歪梯

发布于 2020-06-19 16:18:40

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发布于 2020-06-19 16:18:40

文章被收录于专栏：歪歪梯Club

future

future代表一个任务的预执行结果，通过get方法获取执行结果

    public interface Future<V> {
        V get() throws Exception;
    }

callable

callable代表一个要执行的任务，执行方法call，执行完成返回一个值

    public interface Callable<V> {
        V call() throws Exception;
    }

executor

executor为执行器，通过执行器来执行任务并得到预执行结果对象future

    public interface Executor<V> {
        Future<V> execute(Callable<V> callable);
    }

SynchronizedExecutor

使用synchronized关键字实现的执行器

public class SynchronizedExecutor<V> implements Executor<V> {

    static class ExecutorThread<V> extends Thread{
        public Object lock;
        public V result;
        public Callable<V> task;
        public Exception e;
        public boolean isDone = false;
        public ExecutorThread(Callable<V> task,Object lock) {
            this.lock = lock;
            this.task = task;
        }
        @Override
        public void run() {
            try {
                result = task.call();
            } catch (Exception e) {
                this.e = e;
            }finally {
                synchronized (lock) {
                    //需持有锁才能调用notify
                    this.isDone = true;
                    lock.notifyAll();
                    //此处的加锁只是为了获得锁
                }
            }

        }

    }

    @Override
    public Future<V> execute(Callable<V> callable) {
        Object lock = new Object();
        ExecutorThread<V> thread = new ExecutorThread<V>(callable,lock);
        thread.start();
        Future<V> future = new Future<V>() {

            @Override
            public V get() throws Exception {
                synchronized (lock) {
                    //通过锁机制，使得未完成时，get方法陷入等待队列，让出cpu给别的线程，异步完成时再唤醒
                    //需持有锁才能调用wait
                    while(!thread.isDone) {
                        lock.wait();
                    }
                    if(thread.e != null) {
                        throw thread.e;
                    }
                    return thread.result;
                }
            }

        };

        return future;
    }

}