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求FutureTask(Runnable runnable, V result)的简单实例代码

2008-07-01 11:58:30 486 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

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Java FutureTask本质解析：任务状态契约与假异步陷阱 FutureTask是Java并发中连接Callable、ExecutorService和Future的核心契约实现，其本质并非异步工具，而是一个具备状态机（NEW→COMPLETING→NORMAL/EXCEPTIONAL）的可执行任务容器。它通过AtomicInteger管理生命周期，用WaitNode链表+LockSupport.park实现get()阻塞，但所有阻塞行为均取决于state字段而非线程调度。正因如此，未配合超时的get()极易引发线程池耗尽，而isDone()仅表示任务终结（含失败/取阅读详情

近几天对FutureTask(Runnable runnable, V result)的用法百思不得其解。

求一示例代码，要求用runnable在一个线程中生成一个随机数，然后通过result返回。

注：FutureTask是java.util.concurrent包中的类，JDK1.5加入

...全文

Java FutureTask 深度解析：状态机、线程安全与生产级实践 FutureTask 是 Java 并发编程中连接 Runnable 与 Callable 的核心桥梁，其本质是一个基于 volatile 状态字段和 CAS 原子操作实现的精细化状态机。它不仅封装异步计算结果，更通过 NEW→COMPLETING→NORMAL/EXCEPTIONAL 等七种状态流转，保障多线程下结果设置与获取的强一致性；依托 AQS 实现 get() 的高效阻塞与唤醒，避免忙等待与竞态风险。技术价值在于提供可手动执行、可重复提交、可继承扩展的可控任务实体，远超 submit() 返回的只阅读详情

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切换为时间正序

linsingle 2012-02-28

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import java.util.concurrent.FutureTask;

public class FutureCallableDemo {
public static long fibonacci(long n) {
if(n <=1) {
return n;
} else {
return fibonacci(n-1) + fibonacci(n-2);
}
}
/**
* @param args
*/
public static void main(String[] args) {
class Result {
private long result;
}
final Result r = new Result();
FutureTask<Result> fib30 = new FutureTask<>(
new Runnable() {
@Override
public void run() {
r.result = fibonacci(30);
}

}
, r);
System.out.println("老闆,我要第30個費式數,待會來拿...");
new Thread(fib30).start();
System.out.println("忙別的事去...");
try {
Thread.sleep(5000);
System.out.printf("第30個費式數:%d%n", fib30.get().result);
} catch(Exception ex) {
ex.printStackTrace();
}
}

}

tmyaio 2012-01-15

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34.public class FutureTask<V> implements Future<V>, Runnable {
35. /** Synchronization control for FutureTask */
36. private final Sync sync;
37.
38. /**
39. * Creates a <tt>FutureTask</tt> that will upon running, execute the
40. * given <tt>Callable</tt>.
41. *
42. * @param callable the callable task
43. * @throws NullPointerException if callable is null
44. */
45. public FutureTask(Callable<V> callable) {
46. if (callable == null)
47. throw new NullPointerException();
48. sync = new Sync(callable);
49. }
50.
51. /**
52. * Creates a <tt>FutureTask</tt> that will upon running, execute the
53. * given <tt>Runnable</tt>, and arrange that <tt>get</tt> will return the
54. * given result on successful completion.
55. *
56. * @param runnable the runnable task
57. * @param result the result to return on successful completion. If
58. * you don't need a particular result, consider using
59. * constructions of the form:
60. * <tt>Future<?> f = new FutureTask<Object>(runnable, null)</tt>
61. * @throws NullPointerException if runnable is null
62. */
63. public FutureTask(Runnable runnable, V result) {
64. sync = new Sync(Executors.callable(runnable, result));
65. }
66.
67. public boolean isCancelled() {
68. return sync.innerIsCancelled();
69. }
70.
71. public boolean isDone() {
72. return sync.innerIsDone();
73. }
74.
75. public boolean cancel(boolean mayInterruptIfRunning) {
76. return sync.innerCancel(mayInterruptIfRunning);
77. }
78.
79. public V get() throws InterruptedException, ExecutionException {
80. return sync.innerGet();
81. }
82.
83. public V get(long timeout, TimeUnit unit)
84. throws InterruptedException, ExecutionException, TimeoutException {
85. return sync.innerGet(unit.toNanos(timeout));
86. }
87.
88. /**
89. * Protected method invoked when this task transitions to state
90. * <tt>isDone</tt> (whether normally or via cancellation). The
91. * default implementation does nothing. Subclasses may override
92. * this method to invoke completion callbacks or perform
93. * bookkeeping. Note that you can query status inside the
94. * implementation of this method to determine whether this task
95. * has been cancelled.
96. */
97. protected void done() { }
98.
99. /**
100. * Sets the result of this Future to the given value unless
101. * this future has already been set or has been cancelled.
102. * @param v the value
103. */
104. protected void set(V v) {
105. sync.innerSet(v);
106. }
107.
108. /**
109. * Causes this future to report an <tt>ExecutionException</tt>
110. * with the given throwable as its cause, unless this Future has
111. * already been set or has been cancelled.
112. * @param t the cause of failure.
113. */
114. protected void setException(Throwable t) {
115. sync.innerSetException(t);
116. }
117.
118. /**
119. * Sets this Future to the result of computation unless
120. * it has been cancelled.
121. */
122. public void run() {
123. sync.innerRun();
124. }
125.
126. /**
127. * Executes the computation without setting its result, and then
128. * resets this Future to initial state, failing to do so if the
129. * computation encounters an exception or is cancelled. This is
130. * designed for use with tasks that intrinsically execute more
131. * than once.
132. * @return true if successfully run and reset
133. */
134. protected boolean runAndReset() {
135. return sync.innerRunAndReset();
136. }
137.
138. /**
139. * Synchronization control for FutureTask. Note that this must be
140. * a non-static inner class in order to invoke the protected
141. * <tt>done</tt> method. For clarity, all inner class support
142. * methods are same as outer, prefixed with "inner".
143. *
144. * Uses AQS sync state to represent run status
145. */
146. private final class Sync extends AbstractQueuedSynchronizer {
147. /** State value representing that task is running */
148. private static final int RUNNING = 1;
149. /** State value representing that task ran */
150. private static final int RAN = 2;
151. /** State value representing that task was cancelled */
152. private static final int CANCELLED = 4;
153.
154. /** The underlying callable */
155. private final Callable<V> callable;
156. /** The result to return from get() */
157. private V result;
158. /** The exception to throw from get() */
159. private Throwable exception;
160.
161. /**
162. * The thread running task. When nulled after set/cancel, this
163. * indicates that the results are accessible. Must be
164. * volatile, to ensure visibility upon completion.
165. */
166. private volatile Thread runner;
167.
168. Sync(Callable<V> callable) {
169. this.callable = callable;
170. }
171.
172. private boolean ranOrCancelled(int state) {
173. return (state & (RAN | CANCELLED)) != 0;
174. }
175.
176. /**
177. * Implements AQS base acquire to succeed if ran or cancelled
178. */
179. protected int tryAcquireShared(int ignore) {
180. return innerIsDone()? 1 : -1;
181. }
182.
183. /**
184. * Implements AQS base release to always signal after setting
185. * final done status by nulling runner thread.
186. */
187. protected boolean tryReleaseShared(int ignore) {
188. runner = null;
189. return true;
190. }
191.
192. boolean innerIsCancelled() {
193. return getState() == CANCELLED;
194. }
195.
196. boolean innerIsDone() {
197. return ranOrCancelled(getState()) && runner == null;
198. }
199.
200. V innerGet() throws InterruptedException, ExecutionException {
201. acquireSharedInterruptibly(0);
202. if (getState() == CANCELLED)
203. throw new CancellationException();
204. if (exception != null)
205. throw new ExecutionException(exception);
206. return result;
207. }
208.
209. V innerGet(long nanosTimeout) throws InterruptedException, ExecutionException, TimeoutException {
210. if (!tryAcquireSharedNanos(0, nanosTimeout))
211. throw new TimeoutException();
212. if (getState() == CANCELLED)
213. throw new CancellationException();
214. if (exception != null)
215. throw new ExecutionException(exception);
216. return result;
217. }
218.
219. void innerSet(V v) {
220. for (;;) {
221. int s = getState();
222. if (ranOrCancelled(s))
223. return;
224. if (compareAndSetState(s, RAN))
225. break;
226. }
227. result = v;
228. releaseShared(0);
229. done();
230. }
231.
232. void innerSetException(Throwable t) {
233. for (;;) {
234. int s = getState();
235. if (ranOrCancelled(s))
236. return;
237. if (compareAndSetState(s, RAN))
238. break;
239. }
240. exception = t;
241. result = null;
242. releaseShared(0);
243. done();
244. }
245.
246. boolean innerCancel(boolean mayInterruptIfRunning) {
247. for (;;) {
248. int s = getState();
249. if (ranOrCancelled(s))
250. return false;
251. if (compareAndSetState(s, CANCELLED))
252. break;
253. }
254. if (mayInterruptIfRunning) {
255. Thread r = runner;
256. if (r != null)
257. r.interrupt();
258. }
259. releaseShared(0);
260. done();
261. return true;
262. }
263.
264. void innerRun() {
265. if (!compareAndSetState(0, RUNNING))
266. return;
267. try {
268. runner = Thread.currentThread();
269. innerSet(callable.call());
270. } catch(Throwable ex) {
271. innerSetException(ex);
272. }
273. }
274.
275. boolean innerRunAndReset() {
276. if (!compareAndSetState(0, RUNNING))
277. return false;
278. try {
279. runner = Thread.currentThread();
280. callable.call(); // don't set result
281. runner = null;
282. return compareAndSetState(RUNNING, 0);
283. } catch(Throwable ex) {
284. innerSetException(ex);
285. return false;
286. }
287. }
288. }
289.}