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CountDownLatch v Javi

CountDownLatch se uporablja za zagotovitev, da opravilo čaka na druge niti, preden se začne. Da bi razumeli njegovo uporabo, razmislimo o strežniku, kjer se lahko glavna naloga začne šele, ko se zaženejo vse zahtevane storitve. Delovanje CountDownLatch: Ko ustvarimo objekt CountDownLatch, določimo število niti, ki naj počakajo, da morajo vse te niti opraviti odštevanje, tako da pokličemo CountDownLatch.countDown(), ko so dokončane ali pripravljene na opravilo. Takoj ko štetje doseže nič, se čakajoča naloga začne izvajati. Primer CountDownLatch v JAVI: Java 
// Java Program to demonstrate how  // to use CountDownLatch Its used  // when a thread needs to wait for other  // threads before starting its work. import java.util.concurrent.CountDownLatch; public class CountDownLatchDemo {  public static void main(String args[])   throws InterruptedException  {  // Let us create task that is going to   // wait for four threads before it starts  CountDownLatch latch = new CountDownLatch(4);  // Let us create four worker   // threads and start them.  Worker first = new Worker(1000 latch   'WORKER-1');  Worker second = new Worker(2000 latch   'WORKER-2');  Worker third = new Worker(3000 latch   'WORKER-3');  Worker fourth = new Worker(4000 latch   'WORKER-4');  first.start();  second.start();  third.start();  fourth.start();  // The main task waits for four threads  latch.await();  // Main thread has started  System.out.println(Thread.currentThread().getName() +  ' has finished');  } } // A class to represent threads for which // the main thread waits. class Worker extends Thread {  private int delay;  private CountDownLatch latch;  public Worker(int delay CountDownLatch latch  String name)  {  super(name);  this.delay = delay;  this.latch = latch;  }  @Override  public void run()  {  try  {  Thread.sleep(delay);  latch.countDown();  System.out.println(Thread.currentThread().getName()  + ' finished');  }  catch (InterruptedException e)  {  e.printStackTrace();  }  } }
Izhod: 
WORKER-1 finished WORKER-2 finished WORKER-3 finished WORKER-4 finished main has finished
Dejstva o CountDownLatch:
  1. Ustvarjanje objekta CountDownLatch s posredovanjem int njegovemu konstruktorju (štetje) je dejansko število povabljenih strank (niti) za dogodek.
  2. Nit, ki je odvisna od drugih niti za začetek obdelave, čaka, dokler vsaka druga nit ne pokliče odštevanja. Vse niti, ki čakajo na await(), nadaljujejo skupaj, ko odštevanje doseže nič.
  3. Metoda countDown() zmanjšuje metodo count in await(), dokler ni count == 0