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

        if (count == 0) {
            if (latch.getCount() != 0) {
                latch.countDown();
            }
        } else if (latch.getCount() == 0) {
            latch = new CountDownLatch(1);
        }


        this.count = count;
    }

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    RenderingErrorObserver previousRenderingErrorObserver = getRenderingErrorObserver();
    try {
      // Replace current rendering error observer by a listener that counts down
      // a latch to check further if a rendering error happened during off screen rendering
      // (rendering error listener is called from a notification thread)
      final CountDownLatch latch = new CountDownLatch(1); 
      setRenderingErrorObserver(new RenderingErrorObserver() {
          public void errorOccured(int errorCode, String errorMessage) {
            latch.countDown();
          }
        });
      
      // Create an off screen canvas and bind it to view
      offScreenCanvas = getOffScreenCanvas3D(width, height);
      view.addCanvas3D(offScreenCanvas);
      
      // Render off screen canvas
      offScreenCanvas.renderOffScreenBuffer();
      offScreenCanvas.waitForOffScreenRendering();
      
      // If latch count becomes equal to 0 during the past instructions or in the coming 10 milliseconds, 
      // this means that a rendering error happened
      if (latch.await(10, TimeUnit.MILLISECONDS)) {
        throw new IllegalRenderingStateException("Off screen rendering unavailable");
      }
      
      return offScreenCanvas.getOffScreenBuffer().getImage();
    } catch (InterruptedException ex) {

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    public BroadcasterFuture(Future<?> innerFuture, E msg) {
        this.msg = msg;
        this.innerFuture = innerFuture;
        if (innerFuture == null) {
            latch = new CountDownLatch(1);
        } else {
            latch = null;
        }
    }

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     * @param res    the {@link HttpServletResponse}
     */
    @Override
    protected void suspend(Action action, HttpServletRequest req, HttpServletResponse res)
            throws IOException, ServletException {
        CountDownLatch latch = new CountDownLatch(1);


        req.setAttribute(LATCH, latch.hashCode());
        latchs.put(latch.hashCode(), latch);


        if (supportSession()) {
            // Store as well in the session in case the resume operation
            // happens outside the AtmosphereHandler.onStateChange scope.
            req.getSession().setAttribute(LATCH, latch.hashCode());
        }


        try {
            // Google App Engine doesn't allow a thread to block more than 30 seconds
            if (action.timeout != -1 && action.timeout < 30000) {
                latch.await(action.timeout, TimeUnit.MILLISECONDS);
            }
            else {
                latch.await(20000, TimeUnit.MILLISECONDS);
            }
        }
        catch (Throwable ex) {
            logger.warn("Unable to resume the suspended connection", ex);
        }

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                int latchId = (req.getAttribute(LATCH) == null ? 0 : (Integer)req.getAttribute(LATCH));
                if (req.getSession(true).getAttribute(LATCH) != null) {
                    latchId = (Integer) req.getSession(true).getAttribute(LATCH);
                }
                CountDownLatch latch = latchs.get(latchId);


                if (latch == null && req.getAttribute(AtmosphereResourceImpl.PRE_SUSPEND) == null) {
                    logger.debug("response wasn't suspended: {}", res);
                    return action;
                }


                latch.countDown();
                                                                  
                Action nextAction = resumed(req, res);
                if (nextAction.type == Action.TYPE.SUSPEND) {
                    logger.debug("Suspending after resuming response: {}", res);
                    suspend(action, req, res);

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     * @throws java.io.IOException
     * @throws javax.servlet.ServletException
     */
    protected void suspend(Action action, HttpServletRequest req, HttpServletResponse res)
            throws IOException, ServletException {
        CountDownLatch latch = new CountDownLatch(1);


        int hash = latch.hashCode();
        req.setAttribute(LATCH, hash);
        latchs.put(hash, latch);


        if (supportSession()) {
            // Store as well in the session in case the resume operation
            // happens outside the AtmosphereHandler.onStateChange scope.
            req.getSession().setAttribute(String.valueOf(req.hashCode()), hash);
        }


        try {
            if (action.timeout != -1) {
                latch.await(action.timeout, TimeUnit.MILLISECONDS);
            } else {
                latch.await();
            }
        } catch (InterruptedException ex) {
            logger.debug("", ex);
        } finally {
            latchs.remove(hash);

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        int latchId = -1;


        if (req.getAttribute(LATCH) != null) {
            latchId = (Integer) req.getAttribute(LATCH);
        }
        CountDownLatch latch = latchs.remove(latchId);
        Action a = super.cancelled(req,res);
        latch.countDown();
        return a;        
    }

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                    }
                }


                String s = config.getInitParameter(AtmosphereServlet.RESUME_AND_KEEPALIVE);
                if (latchId != -1 && (s == null || s.equalsIgnoreCase("false"))) {
                    CountDownLatch latch = latchs.remove(latchId);
                    if (latch == null) {
                        logger.error("Unable to resume the suspended connection with latchId: {}", latchId);
                    }
                    else {
                        latch.countDown();
                    }
                }
                else if (req.getAttribute(AtmosphereResourceImpl.PRE_SUSPEND) == null) {
                    logger.error("Unable to resume the suspended connection");
                }

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    @Test(timeOut = 60000)
    public void testResumeOnBroadcast() {
        logger.info("running test: testResumeOnBroadcast");


        final CountDownLatch latch = new CountDownLatch(1);
        servletLatch = new CountDownLatch(1);
        AsyncHttpClient c = new AsyncHttpClient();
        try {
            long currentTime = System.currentTimeMillis();
            final AtomicReference<Response> r = new AtomicReference();
            c.prepareGet(urlTarget).execute(new AsyncCompletionHandler<Response>() {


                @Override
                public Response onCompleted(Response response) throws Exception {
                    r.set(response);
                    latch.countDown();
                    return response;
                }
            });


            servletLatch.await();


            Broadcaster b = BroadcasterFactory.getDefault().lookup(DefaultBroadcaster.class, "/*");
            assertNotNull(b);
            b.broadcast("resume").get();


            try {
                latch.await();
            } catch (InterruptedException e) {
                fail(e.getMessage());
                return;
            }

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    }


    @Test(timeOut = 60000)
    public void testBroadcasterScope() {
        logger.info("Running testBroadcasterScope");
        final CountDownLatch latch = new CountDownLatch(1);
        final CountDownLatch latch2 = new CountDownLatch(1);


        servletLatch = new CountDownLatch(1);
        AsyncHttpClient c = new AsyncHttpClient();
        Broadcaster b = null;
        try {
            long currentTime = System.currentTimeMillis();
            final AtomicReference<Response> r = new AtomicReference();
            c.prepareGet(urlTarget).execute(new AsyncCompletionHandler<Response>() {


                @Override
                public Response onCompleted(Response response) throws Exception {
                    r.set(response);
                    latch.countDown();
                    return response;
                }
            });


            servletLatch.await();


            String id = broadcasterId.get();


            b = BroadcasterFactory.getDefault().lookup(DefaultBroadcaster.class, id);
            assertNotNull(b);
            b.broadcast("resume").get();


            try {
                latch.await();
            } catch (InterruptedException e) {
                fail(e.getMessage());
                return;
            }


            long time = System.currentTimeMillis() - currentTime;
            if (time < 5000) {
                assertTrue(true);
            } else {
                assertFalse(false);
            }
            assertNotNull(r.get());
            assertEquals(r.get().getStatusCode(), 200);
            String resume = r.get().getResponseBody();
            assertEquals(resume, "resumeresume");


            c.prepareGet(urlTarget).execute(new AsyncCompletionHandler<Response>() {


                @Override
                public Response onCompleted(Response response) throws Exception {
                    r.set(response);
                    latch2.countDown();
                    return response;
                }
            });


            try {
                latch2.await();
            } catch (InterruptedException e) {
                fail(e.getMessage());
                return;
            }

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