Examples of java.util.concurrent.CountDownLatch

java.util.concurrent.CountDownLatch
void main() throws InterruptedException { CountDownLatch startSignal = new CountDownLatch(1); CountDownLatch doneSignal = new CountDownLatch(N); for (int i = 0; i < N; ++i) // create and start threads new Thread(new Worker(startSignal, doneSignal)).start(); doSomethingElse(); // don't let run yet startSignal.countDown(); // let all threads proceed doSomethingElse(); doneSignal.await(); // wait for all to finish } } class Worker implements Runnable { private final CountDownLatch startSignal; private final CountDownLatch doneSignal; Worker(CountDownLatch startSignal, CountDownLatch doneSignal) { this.startSignal = startSignal; this.doneSignal = doneSignal; } public void run() { try { startSignal.await(); doWork(); doneSignal.countDown(); } catch (InterruptedException ex) {} // return; } void doWork() { ... } }}
Another typical usage would be to divide a problem into N parts, describe each part with a Runnable that executes that portion and counts down on the latch, and queue all the Runnables to an Executor. When all sub-parts are complete, the coordinating thread will be able to pass through await. (When threads must repeatedly count down in this way, instead use a {@link CyclicBarrier}.)
```
  {@code}class Driver2  // ... void main() throws InterruptedException { CountDownLatch doneSignal = new CountDownLatch(N); Executor e = ... for (int i = 0; i < N; ++i) // create and start threads e.execute(new WorkerRunnable(doneSignal, i)); doneSignal.await();           // wait for all to finish } } class WorkerRunnable implements Runnable { private final CountDownLatch doneSignal; private final int i; WorkerRunnable(CountDownLatch doneSignal, int i) { this.doneSignal = doneSignal; this.i = i; } public void run() { try { doWork(i); doneSignal.countDown(); } catch (InterruptedException ex) {} // return; } void doWork() { ... } }}
```
Memory consistency effects: Until the count reaches zero, actions in a thread prior to calling {@code countDown()}happen-before actions following a successful return from a corresponding {@code await()} in another thread. @since 1.5 @author Doug Lea


    // Failing test for https://github.com/joewalnes/webbit/issues/29
    @Test
    @Ignore
    public void stopsServerCleanlyAlsoWhenClientsAreConnected() throws Exception {
        final CountDownLatch stopper = new CountDownLatch(1);
        final WebServer server = new NettyWebServer(Executors.newSingleThreadScheduledExecutor(), 9080).start();
        server.add(new HttpHandler() {
            @Override
            public void handleHttpRequest(HttpRequest request, HttpResponse response, HttpControl control) throws Exception {
                System.out.println("We got here");
                server.stop().join();
                System.out.println("But never here");
                stopper.countDown();
            }
        });
        Socket client = new Socket(InetAddress.getLocalHost(), 9080);
        OutputStream http = client.getOutputStream();
        http.write(("" +
                "GET /index.html HTTP/1.1\r\n" +
                "Host: www.example.com\r\n\r\n").getBytes("UTF-8"));
        http.flush();


        assertTrue("Server should have stopped by now", stopper.await(1000, TimeUnit.MILLISECONDS));
    }

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      /*
       * Go to sleep and wait for entry to become available.
       */
      try {
        if (resultAvailabilitySignal == null) {
          resultAvailabilitySignal = new CountDownLatch(1);
        }
        resultAvailabilitySignal.await();
        
        return getResult();
      } catch (InterruptedException e) {

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  }


  private void parse(StreamSource source, String baseURI)
    throws IOException, RDFParseException, RDFHandlerException
  {
    CountDownLatch latch = new CountDownLatch(1);
    PipedInputStream pipe = new PipedInputStream();
    PipedOutputStream out = new PipedOutputStream(pipe);


    try {
      parse(pipe, baseURI, latch);

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     */
    public Command(CommandType type, CommandOutput<T> output, CommandArgs args) {
        this.type   = type;
        this.output = output;
        this.args   = args;
        this.latch  = new CountDownLatch(1);
    }

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        QueryModel query)
    {
      this.executor = executor;
      this.members = members;
      int count = new PatternCounter(query).count();
      this.latch = new CountDownLatch(count * members.size());
      query.visit(this);
    }

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    resultCount = verifyQueryResult(iter, 1);
    assertEquals("Wrong number of query results", 2, resultCount);
  }


  public void testMultiThreadedAccess() {
    final CountDownLatch latch = new CountDownLatch(1);


    Runnable runnable = new Runnable() {


      SailConnection sharedCon = con;


      public void run() {
        assertTrue(sharedCon != null);


        try {
          latch.countDown();
          latch.await();
          sharedCon.addStatement(painter, RDF.TYPE, RDFS.CLASS);


          // wait a bit to allow other thread to add stuff as well.
          Thread.sleep(500L);
          Cursor<? extends Statement> result = sharedCon.getStatements(null, null, null, true);


          int numberOfStatements = 0;
          Statement st;
          while ((st = result.next()) != null) {
            numberOfStatements++;
            assertTrue(st.getSubject().equals(painter) || st.getSubject().equals(picasso));
            assertTrue(st.getPredicate().equals(RDF.TYPE));
            assertTrue(st.getObject().equals(RDFS.CLASS) || st.getObject().equals(painter));
          }
          assertTrue("we should have retrieved statements from both threads", numberOfStatements == 2);


        }
        catch (StoreException e) {
          e.printStackTrace();
          fail(e.getMessage());
        }
        catch (InterruptedException e) {
          fail(e.getMessage());
        }


        // let this thread sleep so the other thread can invoke close()
        // first.
        try {
          Thread.sleep(1000L);


          // the connection should now be closed (by the other thread),
          // invoking any further operation should cause a
          // IllegalStateException
          sharedCon.getStatements(null, null, null, true);
          fail("expected a ConnectionClosedException");
        }
        catch (ConnectionClosedException e) {
          // do nothing, this is the expected behaviour
        }
        catch (Exception e) {
          e.printStackTrace();
          fail("expected a ConnectionClosedException");
        }
      }
    }; // end anonymous class declaration


    // execute the other thread
    Thread newThread = new Thread(runnable, "B (parallel)");
    newThread.start();


    try {
      latch.countDown();
      latch.await();
      con.addStatement(picasso, RDF.TYPE, painter);
      // let this thread sleep to enable other thread to finish its business.
      Thread.sleep(1000L);
      con.close();
    }

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     * a convenient way of keeping the main thread alive whilst gstreamer 
     * processing on other threads continues.
     */
    public static void main() {
        try {
            CountDownLatch latch = quit;
            if (latch != null) {
                latch.await();
            }
        } catch (InterruptedException ex) {
        } finally {
            quit = new CountDownLatch(1);
        }
    }

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            executorService = new MainContextExecutorService(mainContext);
        } else {
            mainContext = new GMainContext();
            executorService = Executors.newSingleThreadScheduledExecutor(threadFactory);
        }
        quit = new CountDownLatch(1);
        return argv.toStringArray();
    }

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 * A simple pipeline, demonstrating media tag detection
 */
public class TagFinder {
    private static final String progname = "TagFinder";
    public static void main(String[] args) {
        final CountDownLatch done = new CountDownLatch(1);
        
        //
        // Initialize the gstreamer framework, and let it interpret any command
        // line flags it is interested in.
        //
        args = Gst.init(progname, args);
        
        if (args.length < 0) {
            System.out.println("Usage: " + progname + " <filename>");
            System.exit(1);
        }
        //
        // Instead of using a playbin, it would be possible to use a pipe
        // a typefind element and a demux and wire them up manually.
        // 
        final PlayBin2 pipe = new PlayBin2(progname);
        pipe.setInputFile(new File(args[0]));
        FakeSink audio = (FakeSink) ElementFactory.make("fakesink", "audio-sink");
        FakeSink video = (FakeSink) ElementFactory.make("fakesink", "video-sink");
        pipe.setAudioSink(audio);
        pipe.setVideoSink(video);
        
        pipe.getBus().connect(new Bus.TAG() {
            public void tagsFound(GstObject source, TagList tagList) {
                for (String tag : tagList.getTagNames()) {
                    System.out.println("Found tag " + tag + " = "
                            + tagList.getValue(tag, 0));
                }
            }
        });
        
        //
        // In theory, an ASYNC_DONE from the pipeline corresponds with the demux
        // completing parsing the media file
        //
        pipe.getBus().connect(new Bus.ASYNC_DONE() {
            public void asyncDone(GstObject source) {
                pipe.stop();
                done.countDown();
            }
        });
        audio.set("signal-handoffs", true);
        video.set("signal-handoffs", true);
        
        //
        // As soon as data starts to flow, it means all tags have been found
        //
        BaseSink.HANDOFF handoff = new BaseSink.HANDOFF() {
            public void handoff(BaseSink sink, Buffer buffer, Pad pad) {
                pipe.stop();
                done.countDown();
            }
        };
        audio.connect(handoff);
        video.connect(handoff);
        
        // Start the pipeline playing
        pipe.pause();
        try {
            done.await();
        } catch (InterruptedException ex) {
        }
        pipe.stop();
    }

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      conflict.setUniqueName(SIMPLE_TRIMMED_PATH);
      modsmd.add(conflict);
      
      ExecutorService executor = Executors.newFixedThreadPool(3);
      
      CountDownLatch startLatch = new CountDownLatch(4);
      CountDownLatch finishLatch = new CountDownLatch(3);
      
      DeploymentTask warTask = new DeploymentTask(startLatch, finishLatch, war);
      executor.execute(warTask);
      
      DeploymentTask jarTask = new DeploymentTask(startLatch, finishLatch, jar);
      executor.execute(jarTask);
      
      DeploymentTask appclientTask = new DeploymentTask(startLatch, finishLatch, appClient);
      executor.execute(appclientTask);
      
      startLatch.countDown();
      
      assertTrue(finishLatch.await(5, TimeUnit.SECONDS));
      
      assertNull(warTask.exception);
      assertNull(jarTask.exception);
      assertNull(appclientTask.exception);

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