标签：state swap this runnable ace utc throwable 操作 实现
最近项目需要用到FutureTask异步获取执行结果，并与Callable结合起来运用。
首先，看下FutureTask执行过程：FutureTask可用于异步获取执行结果或取消执行任务的场景。通过传入Runnable或Callable的任务给FutureTask，
直接调用其run方法或者放入线程池执行，然后通过FutureTask的get方法异步获取执行结果。
下面直接看代码。
Service.java ---服务类
//1、new一个线程池，属于成员变量，在项目启动时就初始化 private static final ExecutorService exec = Executors.newFixedThreadPool(100); public FutureTask<List> getFutureTask() { //2、创建FutureTask任务对象，传参Callable FutureTask<List> ft = new FutureTask<List>(new Callable<List>() { //实现Callable的call（）方法 @Override public List call() throws Exception { //3、进行业务操作 List re = ""; //4、返回业务结果 return re; } }); //5、把FutureTask任务提交到线程池 exec.submit(ft); //6、并返回FutureTask return ft; }
Action.java----业务类
//6、获取任务，传参objList（业务参数） FutureTask<List> futureTask = taskService.getFutureTask(); //8、get()获取业务操作结果。 List taskList = futureTask.get(20, TimeUnit.SECONDS);
下面看源码实现
public class FutureTask<V> implements RunnableFuture<V> 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; private Callable<V> callable; private Object outcome; // non-volatile, protected by state reads/writes 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 } //。。。。。。省略 }
FutureTask类实现了RunnableFuture接口，同时RunnableFuture继承了Runnable接口和Future接口。
state修饰变量是volatie，对整个线程是可见的。
outcome ，属于non-valatie，是为了在读写时候做了自我保护
FutureTask提供了2个构造器：FutureTask(Callable<V> callable)和FutureTask(Runnable runnable, V result) 分别实现了Callable和Runnable方法。
调用这个两个构造器时，state状态为NEW
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; }
FutureTask(Callable<V> callable)实现了Callable的call（）方法，并返回V结果
public V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException { if (unit == null) throw new NullPointerException(); int s = state; if (s <= COMPLETING && (s = awaitDone(true, unit.toNanos(timeout))) <= COMPLETING) throw new TimeoutException(); return report(s); } /** * Returns result or throws exception for completed task. * * @param s completed state value */ @SuppressWarnings("unchecked") 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); } protected void set(V v) { if (UNSAFE.compareAndSwapInt(this, stateOffset, NEW, COMPLETING)) { outcome = v; UNSAFE.putOrderedInt(this, stateOffset, NORMAL); // final state finishCompletion(); } }
futureTask.get(20, TimeUnit.SECONDS)，通过get（）方法获取结果，并设定阻塞时间
标签：state swap this runnable ace utc throwable 操作 实现
原文地址：http://www.cnblogs.com/chuangzhijian/p/7308847.html
