Java/Threads/CountDownLatch

An example of CountDownLatch.

   <source lang="java">
 
  

import java.util.concurrent.CountDownLatch;

public class CDLDemo {

 public static void main(String args[]) {
   CountDownLatch cdl = new CountDownLatch(5);
   new MyThread(cdl);
  
   try {
     cdl.await();
   } catch (InterruptedException exc) {
     System.out.println(exc);
   }
   System.out.println("Done");
 }

}

class MyThread implements Runnable {

 CountDownLatch latch;
  
 MyThread(CountDownLatch c) {
   latch = c;
   new Thread(this).start();
 }
  
 public void run() {
   for(int i = 0; i<5; i++) {
     System.out.println(i);
     latch.countDown(); // decrement count
   }
 }

}

 </source>
   
  
 
  

Count Up Down Latch

   <source lang="java">

/* Copyright (c) 2001-2009, The HSQL Development Group

* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* Neither the name of the HSQL Development Group nor the names of its
* contributors may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL HSQL DEVELOPMENT GROUP, HSQLDB.ORG,
* OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

import java.util.concurrent.CountDownLatch; public class CountUpDownLatch {

   CountDownLatch latch;
   int            count;
   public CountUpDownLatch() {
       latch      = new CountDownLatch(1);
       this.count = count;
   }
   public void await() throws InterruptedException {
       if (count == 0) {
           return;
       }
       latch.await();
   }
   public void countDown() {
       count--;
       if (count == 0) {
           latch.countDown();
       }
   }
   public long getCount() {
       return count;
   }
   public void countUp() {
       if (latch.getCount() == 0) {
           latch = new CountDownLatch(1);
       }
       count++;
   }
   public void setCount(int count) {
       if (count == 0) {
           if (latch.getCount() != 0) {
               latch.countDown();
           }
       } else if (latch.getCount() == 0) {
           latch = new CountDownLatch(1);
       }
       this.count = count;
   }

}

 </source>