futuretask源码分析（推荐）源码分析（推荐）
主要介绍了futuretask源码分析（推荐），小编觉得还是挺不错的，这里给大家分享下，供各位参考。
FutureTask只实现RunnableFuture接口：
该接口继承了java.lang.Runnable和Future接口，也就是继承了这两个接口的特性。
1.可以不必直接继承Thread来生成子类，只要实现run方法，且把实例传入到Thread构造函数，Thread就可以执行该实例的
run方法了（ Thread(Runnable) ）。
2.可以让任务独立执行，get获取任务执行结果时，可以阻塞直至执行结果完成。也可以中断执行，判断执行状态等。
FutureTask是一个支持取消行为的异步任务执行器。该类实现了Future接口的方法。
如： 1. 取消任务执行
2. 查询任务是否执行完成
3. 获取任务执行结果（”get“任务必须得执行完成才能获取结果，否则会阻塞直至任务完成）。
注意：一旦任务执行完成，则不能执行取消任务或者重新启动任务。(除非一开始就使用runAndReset模式运行任务)
FutureTask支持执行两种任务， Callable 或者 Runnable的实现类。且可把FutureTask实例交由Executor执行。
源码部分(很简单)：
public class FutureTask<V> implements RunnableFuture<V> {
/*
* Revision notes: This differs from previous versions of this
* class that relied on AbstractQueuedSynchronizer, mainly to
* avoid surprising users about retaining interrupt status during
* cancellation races. Sync control in the current design relies
* on a "state" field updated via CAS to track completion, along
* with a simple Treiber stack to hold waiting threads.
*
* Style note: As usual, we bypass overhead of using
* AtomicXFieldUpdaters and instead directly use Unsafe intrinsics.
*/
/**
* The run state of this task, initially NEW. The run state
* transitions to a terminal state only in methods set,
* setException, and cancel. During completion, state may take on
* transient values of COMPLETING (while outcome is being set) or
* INTERRUPTING (only while interrupting the runner to satisfy a
* cancel(true)). Transitions from these intermediate to final
* states use cheaper ordered/lazy writes because values are unique
* and cannot be further modified.
*
* Possible state transitions:
* NEW -> COMPLETING -> NORMAL
* NEW -> COMPLETING -> EXCEPTIONAL
* NEW -> CANCELLED
* NEW -> INTERRUPTING -> INTERRUPTED
*/
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;
/** The underlying callable; nulled out after running */
private Callable<V> callable;
/** 用来存储任务执行结果或者异常对象,根据任务state在get时候选择返回执行结果还是抛出异常 */
private Object outcome; // non-volatile, protected by state reads/writes
/** 当前运行Run方法的线程 */
private volatile Thread runner;
/** Treiber stack of waiting threads */
private volatile WaitNode waiters;
/**
* Returns result or throws exception for completed task.
*
* @param s completed state value
*/
@SuppressWarnings("unchecked")
private V report(int s) throws ExecutionException {
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