如何处理等待（）通知（）？

Question

这里我有两个运行方法应该相互同步。

轮询类：

     */
public void run() {
    int seqId = 0;
    while(true) {
    List<KpiMessage> list = null;

        try{
            if(!accumulator.isUsed){                
                try {
                    list = fullPoll(seqId);

                    if (!list.isEmpty()) {
                        seqId = list.get(0).getSequence();
                        accumulator.manageIngoing(list);
                    }
                    System.out.println("Updated");                      
                    wait(); 
                } catch (Exception e1) {
                    e1.printStackTrace();

                }
            }

        } catch (Exception e){
            // TODO:
            System.err.println(e.getMessage());
            e.printStackTrace();                
        }
    }

}


/**
 * Method which defines polling of the database and also count the number of Queries
 * @param lastSeq 
 * @return pojo col
 * @throws Exception
 */
public List<KpiMessage> fullPoll(int lastSeq) throws Exception {
    Statement st = dbConnection.createStatement();
    System.out.println("Polling");
    ResultSet rs = st.executeQuery("Select * from msg_new_to_bde where ACTION = 814 and 
    STATUS = 200 order by SEQ DESC");
    List<KpiMessage> pojoCol = new ArrayList<KpiMessage>();
    try {


        while (rs.next()) {
            KpiMessage filedClass = convertRecordsetToPojo(rs);
            pojoCol.add(filedClass);
        }

        for (KpiMessage pojoClass : pojoCol) {
            System.out.print(" " + pojoClass.getSequence());
            System.out.print(" " + pojoClass.getTableName());
            System.out.print(" " + pojoClass.getAction());
            System.out.print(" " + pojoClass.getKeyInfo1());
            System.out.print(" " + pojoClass.getKeyInfo2());
            System.out.print(" "+ pojoClass.getStatus());
            System.out.println(" " + pojoClass.getEntryTime());

        }


    } finally  {
        try {
            st.close();
            rs.close();
        } catch (Exception e) {
            System.err.println(e.getMessage());
            e.printStackTrace();
        }
    }       

处理和更新类：

        public void run() {
    while(true){
        try {
            while(!accumulator.isUsed)
            {
                try {
                System.out.println("Waiting for new outgoingmessages"); 
                    this.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
     Collection<KpiMessage> outgoingQueue = generate(accumulator.outgoingQueue); 
            accumulator.manageOutgoing(outgoingQueue, dbConnection);
        } catch (Exception e) {
            System.err.println(e.getMessage());
            e.printStackTrace();
        }
    }
}
}   

我有一个逻辑错误：

轮询器不仅轮询新消息，而且还从第一个开始一次又一次地读取数据库。

也一次又一次地更新。

如何解决这个同步问题。

Answer 1

您也可以使用BlockingQueue 在线程之间传输数据。

详情请见BlockingQueue。

// The end of the list.
private static final Integer End = -1;

static class Producer implements Runnable {
  final Queue<Integer> queue;
  private int i = 0;

  public Producer(Queue<Integer> queue) {
    this.queue = queue;
  }

  @Override
  public void run() {
    try {
      for (int i = 0; i < 1000; i++) {
        queue.add(i++);
        Thread.sleep(1);
      }
      // Finish the queue.
      queue.add(End);
    } catch (InterruptedException ex) {
      // Just exit.
    }
  }
}

static class Consumer implements Runnable {
  final Queue<Integer> queue;
  private int i = 0;

  public Consumer(Queue<Integer> queue) {
    this.queue = queue;
  }

  @Override
  public void run() {
    boolean ended = false;
    while (!ended) {
      Integer i = queue.poll();
      if ( i != null ) {
        ended = i == End;
        System.out.println(i);
      }
    }
  }
}

public void test() throws InterruptedException {
  Queue queue = new LinkedBlockingQueue();
  Producer p = new Producer(queue);
  Consumer c = new Consumer(queue);
  Thread pt = new Thread(p);
  Thread ct = new Thread(c);
  // Start it all going.
  pt.start();
  ct.start();
  // Close it down
  pt.join();
  ct.join();
}

Answer 2

您应该同步或更确切地说是保持锁定或监控您正在调用wait() 或notify() 的对象。

以下是对您有帮助的：wait() throwing IllegalArgumentException

synchronized(lockObject){

     lockObject.wait(); //you should hold the lock to be able to call wait()
}