java.util.concurrent.CountDownLatch java code examples

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Common ways to obtain CountDownLatch

private void myMethod () {
     CountDownLatch c =new CountDownLatch(count)
List list;new CountDownLatch(list.size())
AtomicReference atomicReference;atomicReference.get()
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}

 @Override public void onFailure(Call<T> call, Throwable t) {
  failureRef.set(t);
  latch.countDown();
 }
});

 /** Visible for testing. */
 void setListBytes(byte[] publicSuffixListBytes, byte[] publicSuffixExceptionListBytes) {
  this.publicSuffixListBytes = publicSuffixListBytes;
  this.publicSuffixExceptionListBytes = publicSuffixExceptionListBytes;
  listRead.set(true);
  readCompleteLatch.countDown();
 }
}

 @Override
 public void run() {
  try {
   cacheRef.get().getUnchecked(3);
  } finally {
   doneSignal.countDown();
  }
 }
};

 @Override
 public T load(T key) throws InterruptedException {
  if (shouldWait.get()) {
   delayLatch.await();
  }
  return key;
 }
}

 @Override
 public void run() {
  try {
   okayToRun.await();
  } catch (InterruptedException e) {
   Thread.currentThread().interrupt();
   throw new RuntimeException(e);
  }
  runCalled.getAndIncrement();
 }
},

  @Override
  public void run() {
    started.countDown();
    FileUtils.waitFor(new File(""), 2);
    wasInterrupted.set( Thread.currentThread().isInterrupted());
  }
};

 @Override
 public void run()
 {
  try {
   start.await();
  }
  catch (InterruptedException e) {
   throw Throwables.propagate(e);
  }
  final Random rndGen = new Random();
  while (!done.get()) {
   Integer idx = rndGen.nextInt(queryableIndex.get() + 1);
   Assert.assertEquals(idx, concurrentIndexible.get(idx));
  }
 }
}

@GwtIncompatible // threads
public void testSubmitAsync_asyncCallable_cancelledBeforeApplyingFunction()
  throws InterruptedException {
 final AtomicBoolean callableCalled = new AtomicBoolean();
 AsyncCallable<Integer> callable =
   new AsyncCallable<Integer>() {
    @Override
    public ListenableFuture<Integer> call() {
     callableCalled.set(true);
     return immediateFuture(1);
    }
   };
 ExecutorService executor = newSingleThreadExecutor();
 // Pause the executor.
 final CountDownLatch beforeFunction = new CountDownLatch(1);
 executor.execute(
   new Runnable() {
    @Override
    public void run() {
     awaitUninterruptibly(beforeFunction);
    }
   });
 ListenableFuture<Integer> future = submitAsync(callable, executor);
 future.cancel(false);
 // Unpause the executor.
 beforeFunction.countDown();
 executor.shutdown();
 assertTrue(executor.awaitTermination(5, SECONDS));
 assertFalse(callableCalled.get());
}

@Test
public void testServerConnectionHandler() throws Exception {
 AtomicInteger status = new AtomicInteger();
 AtomicReference<HttpConnection> connRef = new AtomicReference<>();
 server.connectionHandler(conn -> {
  assertEquals(0, status.getAndIncrement());
  assertNull(connRef.getAndSet(conn));
 });
 server.requestHandler(req -> {
  assertEquals(1, status.getAndIncrement());
  assertSame(connRef.get(), req.connection());
  req.response().end();
 });
 CountDownLatch listenLatch = new CountDownLatch(1);
 server.listen(onSuccess(s -> listenLatch.countDown()));
 awaitLatch(listenLatch);
 client.getNow(DEFAULT_HTTP_PORT, DEFAULT_HTTP_HOST, "/somepath", resp -> {
  testComplete();
 });
 await();
}

 @Override
 public String load(String key) throws InterruptedException {
  callCount.incrementAndGet();
  startSignal.await();
  throw e;
 }
});

@Test
public void testListenableFuture() throws Exception {
 final AtomicInteger statusCode = new AtomicInteger(500);
 try (AsyncHttpClient ahc = asyncHttpClient()) {
  final CountDownLatch latch = new CountDownLatch(1);
  final ListenableFuture<Response> future = ahc.prepareGet(getTargetUrl()).execute();
  future.addListener(() -> {
   try {
    statusCode.set(future.get().getStatusCode());
    latch.countDown();
   } catch (InterruptedException | ExecutionException e) {
    e.printStackTrace();
   }
  }, Executors.newFixedThreadPool(1));
  latch.await(10, TimeUnit.SECONDS);
  assertEquals(statusCode.get(), 200);
 }
}

 @Test(timeout = 1000L)
 public void get_memoizes() throws InterruptedException {
  int getCount = 1000;

  AtomicInteger value = new AtomicInteger();

  Lazy<Integer> lazyInt = new Lazy<Integer>() {
   final AtomicInteger val = new AtomicInteger();

   @Override protected Integer compute() {
    return val.incrementAndGet();
   }
  };

  CountDownLatch latch = new CountDownLatch(getCount);
  Executor exec = Executors.newFixedThreadPool(10);
  for (int i = 0; i < getCount; i++) {
   exec.execute(() -> {
    // if lazy computes multiple times, the result of lazyInt.get() > 1
    value.getAndAdd(lazyInt.get());
    latch.countDown();
   });
  }
  latch.await();

  assertThat(value.get()).isEqualTo(getCount);
 }
}

@Test
public void tryToReproduceTheIssue() throws Exception
{
  // GIVEN
  GraphDatabaseService db = dbRule.getGraphDatabaseAPI();
  CountDownLatch startSignal = new CountDownLatch( 1 );
  AtomicBoolean stopSignal = new AtomicBoolean();
  AtomicReference<Exception> failure = new AtomicReference<>();
  Node parentNode = createNode( db );
  Collection<Worker> workers = createWorkers( db, startSignal, stopSignal, failure, parentNode );
  // WHEN
  startSignal.countDown();
  sleep( 500 );
  stopSignal.set( true );
  awaitWorkersToEnd( workers );
  // THEN
  if ( failure.get() != null )
  {
    throw new Exception( "A worker failed", failure.get() );
  }
}

 @Override
 public void run() {
  cache.getUnchecked(s);
  computedCount.incrementAndGet();
  tasksFinished.countDown();
 }
});

AtomicBoolean computationShouldWait = new AtomicBoolean();
CountDownLatch computationLatch = new CountDownLatch(1);
QueuingRemovalListener<String, String> listener = queuingRemovalListener();
final LoadingCache<String, String> cache =
 expectedKeys.add(s);
computationShouldWait.set(true);
final AtomicInteger computedCount = new AtomicInteger();
ExecutorService threadPool = Executors.newFixedThreadPool(nThreads);
final CountDownLatch tasksFinished = new CountDownLatch(nTasks);
for (int i = 0; i < nTasks; i++) {
 final String s = "a" + i;
 @SuppressWarnings("unused") // go/futurereturn-lsc
 Future<?> possiblyIgnoredError =
   threadPool.submit(
     new Runnable() {
      @Override
computationLatch.countDown();
while (computedCount.get() < nThreads) {
 Thread.yield();
tasksFinished.await();

@Test
public void testHttpClientConnectionCloseAfterRequestEnd() throws Exception {
 CountDownLatch started = new CountDownLatch(1);
 client = vertx.createHttpClient();
 AtomicReference<EndpointMetric> endpointMetrics = new AtomicReference<>();
 server = vertx.createHttpServer().requestHandler(req -> {
  endpointMetrics.set(((FakeHttpClientMetrics)FakeHttpClientMetrics.getMetrics(client)).endpoint("localhost:8080"));
  req.response().end();
 }).listen(8080, "localhost", ar -> {
  assertTrue(ar.succeeded());
  started.countDown();
 });
 awaitLatch(started);
 CountDownLatch closed = new CountDownLatch(1);
 HttpClientRequest req = client.get(8080, "localhost", "/somepath");
 req.handler(resp -> {
   HttpConnection conn = req.connection();
   conn.closeHandler(v2 -> {
    closed.countDown();
   });
   conn.close();
 req.end();
 awaitLatch(closed);
 EndpointMetric val = endpointMetrics.get();
 assertWaitUntil(() -> val.connectionCount.get() == 0);
 assertEquals(0, val.queueSize.get());
 assertEquals(0, val.requests.get());

 @Override
 public Integer call() throws Exception {
  enterLatch.countDown();
  try {
   new CountDownLatch(1).await(); // wait forever
   throw new AssertionError();
  } catch (InterruptedException e) {
   interruptedExceptionThrown.set(true);
   throw e;
  } finally {
  }
 }
});

 startLatch.await();
 stopLatch.countDown();
 return;
   final float indexedVal = indexed2.get(j);
   if (Floats.compare(val, indexedVal) != 0) {
    failureHappened.set(true);
    reason.set(StringUtils.format("Thread2[%d]: %f != %f", j, val, indexedVal));
    stopLatch.countDown();
    return;
 reason.set(e.getMessage());
 failureHappened.set(true);
stopLatch.countDown();

 countMap.put(msg.body().getString("deploymentID"), msg.body().getInteger("count"));
});
CountDownLatch latch = new CountDownLatch(1);
AtomicReference<String> deploymentID1 = new AtomicReference<>();
AtomicReference<String> deploymentID2 = new AtomicReference<>();
  setIsolationGroup(group1).setIsolatedClasses(isolatedClasses), ar -> {
  assertTrue(ar.succeeded());
  deploymentID1.set(ar.result());
  assertEquals(0, TestVerticle.instanceCount.get());
  vertx.deployVerticle(verticleID,
   new DeploymentOptions().setIsolationGroup(group2).setIsolatedClasses(isolatedClasses), ar2 -> {
   assertTrue(ar2.succeeded());
   deploymentID2.set(ar2.result());
   assertEquals(0, TestVerticle.instanceCount.get());
   latch.countDown();
  });
 });
 assertEquals(count1, countMap.get(deploymentID1.get()).intValue());
 assertEquals(count2, countMap.get(deploymentID2.get()).intValue());
 assertTrue(expectedSuccess);

ExecutorService exec = Executors.newFixedThreadPool(1);
try {
 server.connectHandler(so -> {
  so.handler(buff -> {
   assertEquals(256, buff.length());
   CountDownLatch latch = new CountDownLatch(1);
   exec.execute(() -> {
    latch.countDown();
    so.write(expected);
   });
 });
 startServer();
 AtomicInteger done = new AtomicInteger();
 for (int i = 0;i < num;i++) {
  client.connect(testAddress, ar -> {
     assertEquals(expected, buff);
     so.close();
     int val = done.incrementAndGet();
     if (val == num) {
      testComplete();
 exec.shutdown();

Javadoc

A synchronization aid that allows one or more threads to wait until a set of operations being performed in other threads completes.

A CountDownLatch is initialized with a given count. The #await methods block until the current count reaches zero due to invocations of the #countDown method, after which all waiting threads are released and any subsequent invocations of #await return immediately. This is a one-shot phenomenon -- the count cannot be reset. If you need a version that resets the count, consider using a CyclicBarrier.

A CountDownLatch is a versatile synchronization tool and can be used for a number of purposes. A CountDownLatch initialized with a count of one serves as a simple on/off latch, or gate: all threads invoking #awaitwait at the gate until it is opened by a thread invoking #countDown. A CountDownLatch initialized to N can be used to make one thread wait until N threads have completed some action, or some action has been completed N times.

A useful property of a CountDownLatch is that it doesn't require that threads calling countDown wait for the count to reach zero before proceeding, it simply prevents any thread from proceeding past an #await until all threads could pass.

Sample usage: Here is a pair of classes in which a group of worker threads use two countdown latches:

The first is a start signal that prevents any worker from proceeding until the driver is ready for them to proceed;
The second is a completion signal that allows the driver to wait until all workers have completed.

  
class Driver { // ...} 
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 CyclicBarrier.)

  
class Driver2 { // ...} 
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 countDown()happen-before actions following a successful return from a corresponding await() in another thread.

Most used methods

countDown
Decrements the count of the latch, releasing all waiting threads if the count reaches zero.If the cu
await
Causes the current thread to wait until the latch has counted down to zero, unless the thread is Thr
<init>
Constructs a CountDownLatch initialized with the given count.
getCount
Returns the current count.This method is typically used for debugging and testing purposes.
toString
Returns a string identifying this latch, as well as its state. The state, in brackets, includes the

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