这段代码中的错误在哪里？

我创建了一个用作缓存提供者的类。它使用一个Map，时间戳映射条目，它产生一个Thread，每隔一段时间执行一次清理。该类用于Web应用程序。这个Web应用程序有一个问题，POST需要30秒。我将问题追溯到这个缓存类，消除了它解决了问题。这段代码中的错误在哪里？

我已尽全力在本课中找到错误，但我不能。请帮我在这里。假设用户类是某种描述用户的POJO。

public class UserStore implements Thread.UncaughtExceptionHandler { 
private static volatile UserStore instance; 
private static Thread cleanUpThread; 
private static Map<String, TimeStampedToken<User>> tokenMap = new HashMap<String, TimeStampedToken<User>>(); 
public static UserStore getInstance() { 
    if (instance == null) { 
     synchronized(UserStore.class) { 
      if (instance == null) { 
       instance = new UserStore(); 
       cleanUpThread = new Thread(new CleanUpWorker()); 
       cleanUpThread.setUncaughtExceptionHandler(instance); 
       cleanUpThread.start(); 
      } 
     } 
    } 
    return instance; 
} 
public void uncaughtException(Thread thread, Throwable throwable) { 
    if (throwable instanceof ThreadDeath) { 
     cleanUpThread = new Thread(new CleanUpWorker()); 
     cleanUpThread.setUncaughtExceptionHandler(this); 
     cleanUpThread.start(); 
     throw (ThreadDeath)throwable; 
    } 

} 
private static class CleanUpWorker implements Runnable { 
    private static final long CLEANUP_CYCLE_MS = 300000; 
    private static final long OBJECT_LIVE_TIME = 299900; 
    public void run() { 
     long sleepRemaining; 
     long sleepStart = System.currentTimeMillis(); 
     sleepRemaining = CLEANUP_CYCLE_MS; 
     while (true) { 
      try { 
       sleepStart = System.currentTimeMillis(); 
       Thread.sleep(sleepRemaining); 
       cleanUp(); 
       sleepRemaining = CLEANUP_CYCLE_MS; 
      } catch (InterruptedException e) { 
       sleepRemaining = System.currentTimeMillis() - sleepStart; 
      } 
     } 
    } 
    private void cleanUp() { 
     Long currentTime = System.currentTimeMillis(); 
     synchronized(tokenMap) { 
      for (String user : tokenMap.keySet()) { 
       TimeStampedToken<User> tok = tokenMap.get(user); 
       if (tok.accessed + OBJECT_LIVE_TIME < currentTime) { 
        tokenMap.remove(user); 
       } 
      } 
     } 
    } 

} 
public void addToken(User tok) { 
    synchronized(tokenMap) { 
     tokenMap.put(tok.getUserId(), new TimeStampedToken<User>(tok)); 
    } 
} 
public User getToken(String userId) { 
    synchronized(tokenMap) { 
     TimeStampedToken<User> user = tokenMap.get(userId); 
     if (user != null) { 
      user.accessed = System.currentTimeMillis(); 
      return user.payload; 
     } else { 
      return null; 
     } 

    } 
} 
private static class TimeStampedToken<E> { 
    public TimeStampedToken(E payload) { 
     this.payload = payload; 
    } 
    public long accessed = System.currentTimeMillis(); 
    public E payload; 
} 
}

来源

2011-12-21 U Mad

究竟是什么*问题，你的缓存类是做什么的？它工作不正确（功能上）？或者它比你想要的慢（导致POST花费太长时间）？如果是这样，哪种方法调用花费太多时间？ – ArjunShankar 2011-12-21 11:19:39

为什么只有在明确告知停止时才重新启动线程？ – 2011-12-21 11:19:53

我看起来像你试图实现一个有效期限的缓存。有很多简单的方法来实现这一点，或者你可以使用已经这样做的库。 – 2011-12-21 11:21:15

下面是我如何接近它。使用多线程代码，简单性通常是最好的方法，因为它更可能工作。

（第三个参数的LinkedHashMap的true意味着，在这个地图迭代器遵循访问的顺序而不是插入的顺序）

public enum UserStore { 
    ; 

    interface User { 
     String getUserId(); 
    } 

    // a LRU cache with a timestamp. 
    private static final Map<String, TimeStampedToken<User>> tokenMap = new LinkedHashMap<String, TimeStampedToken<User>>(16, 0.7f, true); 
    private static final long OBJECT_LIVE_TIME = 299900; 

    public static synchronized void addToken(User tok) { 
     final long now = System.currentTimeMillis(); 
     // clean up as we go 
     for (Iterator<Map.Entry<String, TimeStampedToken<User>>> iter = tokenMap.entrySet().iterator(); iter.hasNext();) { 
      final Map.Entry<String, TimeStampedToken<User>> next = iter.next(); 
      if (next.getValue().accessed + OBJECT_LIVE_TIME >= now) 
       // the map is ordered by access time so there are no more to clean up. 
       break; 
      iter.remove(); 
     } 
     // add a new entry 
     tokenMap.put(tok.getUserId(), new TimeStampedToken<User>(tok, now)); 
    } 

    public static synchronized User getToken(String userId) { 
     final long now = System.currentTimeMillis(); 
     TimeStampedToken<User> user = tokenMap.get(userId); 
     if (user == null) 
      return null; 

     user.accessed = now; 
     return user.payload; 
    } 

    static class TimeStampedToken<E> { 
     long accessed; 
     final E payload; 

     TimeStampedToken(E payload, long now) { 
      this.payload = payload; 
      accessed = now; 
     } 
    } 
}

来源

2011-12-21 11:33:17

这行看起来怪我......

sleepRemaining = System.currentTimeMillis（） - sleepStart;

...当然，它应该是...

sleepRemaining = CLEANUP_CYCLE_MS - （System.currentTimeMillis的（） - sleepStart）;

来源

2011-12-21 11:36:04

这段代码中的错误在哪里？

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