在递归块挂起中使用CountDownLatch和Object.wait(Using CountDownLatch & Object.wait inside recursive block hangs)

 问题：在尝试以分阶段方式检索递归块内的值时，执行会挂起。 
 
 描述： CountDownLatch和Object.wait用于实现递归块内的值的分阶段方式访问。 但是，该程序挂起以下输出： 
 
2 < 16
3 < 16
4 < 16
5 < 16
Current total: 5
 Inside of wait
 Inside of wait
 
 程序： 
 
import java.util.concurrent.*;
public class RecursiveTotalFinder {
    private static CountDownLatch latch1;
    private static CountDownLatch latch2;
    private static CountDownLatch latch3;
    public static void main(String... args) {
       latch1 = new CountDownLatch(1);
       latch2 = new CountDownLatch(1);
       latch3 = new CountDownLatch(1);

       //Create object
       TotalFinder tf = new TotalFinder(latch1,latch2,latch3);

       //Start the thread
       tf.start();

       //Wait for results from TotalFinder
       try {
           latch1.await();
       } catch(InterruptedException ie) {
           ie.printStackTrace();
       }

       //Print the result after 5th iteration
       System.out.println("Current total: "+tf.getCurrentTotal());
       tf.releaseWaitLock();
       tf.resetWaitLock();

       //Wait for results again
       try {
           latch2.await();
       } catch(InterruptedException ie) {
           ie.printStackTrace();
       }

       //Print the result after 10th iteration
       System.out.println("Current total: "+tf.getCurrentTotal());
       tf.releaseWaitLock();
       tf.resetWaitLock();

       //Wait for results again
       try {
           latch3.await();
       } catch(InterruptedException ie) {
           ie.printStackTrace();
       }

       //Print the result after 15th iteration
       System.out.println("Current total: "+tf.getCurrentTotal());
       tf.releaseWaitLock();
       tf.resetWaitLock();
    }
}


class TotalFinder extends Thread{
    CountDownLatch tfLatch1;
    CountDownLatch tfLatch2;
    CountDownLatch tfLatch3;
    private static int count = 1;
    private static final class Lock { }
    private final Object lock = new Lock();
    private boolean gotSignalFromMaster = false;

    public TotalFinder(CountDownLatch latch1, CountDownLatch latch2, 
                       CountDownLatch latch3) {
        tfLatch1 = latch1;
        tfLatch2 = latch2;
        tfLatch3 = latch3;
    }

    public void run() {
        findTotal(16);
    }

    //Find total
    synchronized void findTotal(int cnt) {
        if(count%5==0) {
           if(count==5)
              tfLatch1.countDown();
           if(count==10)
              tfLatch2.countDown();
           if(count==15)
              tfLatch3.countDown();

           //Sleep for sometime
           try {
               Thread.sleep(3000);
           } catch(InterruptedException ie) {
               ie.printStackTrace();
           }
           //Wait till current total is printed

           synchronized(lock) {
              while(gotSignalFromMaster==false) {
                 try {
                    System.out.println(" Inside of wait");
                    lock.wait();
                 } catch(InterruptedException ie) {
                    ie.printStackTrace();
                 }
              }
              System.out.println("Came outside of wait");
           }

        }
        count +=1;
        if(count < cnt) {
           System.out.println(count +" < "+cnt);
           findTotal(cnt);
        }
    }

    //Return the count value
    public int getCurrentTotal() {
       return count;
    }

    //Release lock
    public void releaseWaitLock() {
        //Sleep for sometime
        try {
            Thread.sleep(5000);
        } catch(InterruptedException ie) {
            ie.printStackTrace();
        }

        synchronized(lock) {
           gotSignalFromMaster=true;
           lock.notifyAll();
        }
    }

    //Reset wait lock
    public void resetWaitLock() {
        gotSignalFromMaster = false;
    }
}
 
 分析：在我的初步分析中，看起来等待是以递归方式发生的，尽管从主程序调用了notifyAll 。 
 
 帮助：为什么在CountDownLatch没有生效后使用notfiyAll进行免费锁定？ 需要某人帮助了解此计划中究竟发生了什么。 

Problem: While trying to retrieve values inside a recursive block in a phased manner, the execution gets hung. 
 
Description: CountDownLatch & Object.wait are used to achieve the phased manner access of value inside the recursive block. But, the program hangs with following output:
 
2 < 16
3 < 16
4 < 16
5 < 16
Current total: 5
 Inside of wait
 Inside of wait
 
Program:
 
import java.util.concurrent.*;
public class RecursiveTotalFinder {
    private static CountDownLatch latch1;
    private static CountDownLatch latch2;
    private static CountDownLatch latch3;
    public static void main(String... args) {
       latch1 = new CountDownLatch(1);
       latch2 = new CountDownLatch(1);
       latch3 = new CountDownLatch(1);

       //Create object
       TotalFinder tf = new TotalFinder(latch1,latch2,latch3);

       //Start the thread
       tf.start();

       //Wait for results from TotalFinder
       try {
           latch1.await();
       } catch(InterruptedException ie) {
           ie.printStackTrace();
       }

       //Print the result after 5th iteration
       System.out.println("Current total: "+tf.getCurrentTotal());
       tf.releaseWaitLock();
       tf.resetWaitLock();

       //Wait for results again
       try {
           latch2.await();
       } catch(InterruptedException ie) {
           ie.printStackTrace();
       }

       //Print the result after 10th iteration
       System.out.println("Current total: "+tf.getCurrentTotal());
       tf.releaseWaitLock();
       tf.resetWaitLock();

       //Wait for results again
       try {
           latch3.await();
       } catch(InterruptedException ie) {
           ie.printStackTrace();
       }

       //Print the result after 15th iteration
       System.out.println("Current total: "+tf.getCurrentTotal());
       tf.releaseWaitLock();
       tf.resetWaitLock();
    }
}


class TotalFinder extends Thread{
    CountDownLatch tfLatch1;
    CountDownLatch tfLatch2;
    CountDownLatch tfLatch3;
    private static int count = 1;
    private static final class Lock { }
    private final Object lock = new Lock();
    private boolean gotSignalFromMaster = false;

    public TotalFinder(CountDownLatch latch1, CountDownLatch latch2, 
                       CountDownLatch latch3) {
        tfLatch1 = latch1;
        tfLatch2 = latch2;
        tfLatch3 = latch3;
    }

    public void run() {
        findTotal(16);
    }

    //Find total
    synchronized void findTotal(int cnt) {
        if(count%5==0) {
           if(count==5)
              tfLatch1.countDown();
           if(count==10)
              tfLatch2.countDown();
           if(count==15)
              tfLatch3.countDown();

           //Sleep for sometime
           try {
               Thread.sleep(3000);
           } catch(InterruptedException ie) {
               ie.printStackTrace();
           }
           //Wait till current total is printed

           synchronized(lock) {
              while(gotSignalFromMaster==false) {
                 try {
                    System.out.println(" Inside of wait");
                    lock.wait();
                 } catch(InterruptedException ie) {
                    ie.printStackTrace();
                 }
              }
              System.out.println("Came outside of wait");
           }

        }
        count +=1;
        if(count < cnt) {
           System.out.println(count +" < "+cnt);
           findTotal(cnt);
        }
    }

    //Return the count value
    public int getCurrentTotal() {
       return count;
    }

    //Release lock
    public void releaseWaitLock() {
        //Sleep for sometime
        try {
            Thread.sleep(5000);
        } catch(InterruptedException ie) {
            ie.printStackTrace();
        }

        synchronized(lock) {
           gotSignalFromMaster=true;
           lock.notifyAll();
        }
    }

    //Reset wait lock
    public void resetWaitLock() {
        gotSignalFromMaster = false;
    }
}
 
Analysis: In my initial analysis it looks like the wait is happening recursively eventhough notifyAll is invoked from the main program.
 
Help: Why free lock using notfiyAll after a CountDownLatch didn't take effect? Need someone's help in understanding what exactly is happening in this program.

原文：https://stackoverflow.com/questions/29066020