基本原理

• 采用LockSupport的parkNanos和unpack方法
• 在另外一个线程中结果回来，unpack一下，返回；否则就等待超时返回（超时采用一线程轮询 + lock的condITion的await 双重保险）

实例

import java.text.SimpleDateFormat; import java.util.Date; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.TimeUnit; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /**  *   * Created by codecraft on 2015/8/26.  */ public class DefaultFuture {     private static final Map<Long, DefaultFuture> FUTURES = new ConcurrentHashMap<Long, DefaultFuture>();     private final long id;     private final Lock lock = new ReentrantLock();     private final Condition done = lock.newCondition();     private volatile Response response;     private final long start = System.currentTimeMillis();     private final int timeout;     public DefaultFuture(long id,int timeout) {         this.id = id;         this.timeout = timeout;     }     private long getStartTimestamp() {         return start;     }     public int getTimeout() {         return timeout;     }     public boolean isDone() {         return response != null;     }     public long getId() {         return id;     }     public Object get(int timeout){         if (timeout <= 0) {             timeout = 1000;         }         if (! isDone()) {             long start = System.currentTimeMillis();             lock.lock();             try {                 while (! isDone()) {                     done.await(timeout, TimeUnit.MILLISECONDS);                     if (isDone() || System.currentTimeMillis() - start > timeout) {                         break;                     }                 }             } catch (InterruptedException e) {                 throw new RuntimeException(e);             } finally {                 lock.unlock();             }             if (! isDone()) { //                throw new RuntimeException("timeout");                 System.out.println("timeout");             }         }         return response;     }     private void doReceived(Response res) {         lock.lock();         try {             response = res;             if (done != null) {                 done.signal();             }         } finally {             lock.unlock();         }     }     public static void received(Response response) {         try {             DefaultFuture future = FUTURES.remove(response.getId());             if (future != null) {                 future.doReceived(response);             } else {                 System.out.println("The timeout response finally returned at "                         + (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS").format(new Date()))                         + ", response ");             }         } finally { //            CHANNELS.remove(response.getId());         }     }     private static class RemotingInvocationTimeoutScan implements Runnable {         public void run() {             while (true) {                 try {                     for (DefaultFuture future : FUTURES.values()) {                         if (future == null || future.isDone()) {                             continue;                         }                         if (System.currentTimeMillis() - future.getStartTimestamp() > future.getTimeout()) {                             // create exception response.                             Response timeoutResponse = new Response(future.getId());                             // handle response.                             DefaultFuture.received(timeoutResponse);                         }                     }                     Thread.sleep(30);                 } catch (Throwable e) {                     e.printStackTrace();                 }             }         }     }     static {         Thread th = new Thread(new RemotingInvocationTimeoutScan(), "ResponseTimeoutScanTimer");         th.setDaemon(true);         th.start();     }     public static void main(String[] args){         int timeout = 1000;         System.out.println("start");         final long start = System.currentTimeMillis();         final DefaultFuture future = new DefaultFuture(1,timeout);         new Thread(new Runnable() {             @Override             public void run() {                 while (System.currentTimeMillis() - start < 2000) {                     //sleep                 }                 Response response = new Response();                 response.setResult("hello");                 future.doReceived(response);             }         }).start();         Object response = future.get(timeout);         System.out.println(System.currentTimeMillis() - start);         System.out.println("res "+response);     } }

参考

• dubbo-DefaultFuture