assertEquals(Integer.valueOf(50), asMap.get(10));
    assertEquals(null, cache.getIfPresent(2));
    assertEquals(null, asMap.get(2));

    asMap.putIfAbsent(2, 20);
    asMap.putIfAbsent(10, 20);

    assertEquals(Integer.valueOf(20), cache.getIfPresent(2));
    assertEquals(Integer.valueOf(20), asMap.get(2));
    assertEquals(Integer.valueOf(50), cache.getIfPresent(10));

   * zero, associate it with {@code newValue}. Returns the previous value associated with {@code
   * key}, or zero if there was no mapping for {@code key}.
   */
  long putIfAbsent(K key, long newValue) {
    AtomicBoolean noValue = new AtomicBoolean(false);
    Long result =
        map.compute(
            key,
            (k, oldValue) -> {

        Entry<Object, Object> entry = warmed.get(i - WARMUP_MIN);
        Object newValue = new Object();
        assertSame(entry.getValue(), cache.asMap().putIfAbsent(entry.getKey(), newValue));
        Object newKey = new Object();
        assertNull(cache.asMap().putIfAbsent(newKey, entry.getValue()));
        // this getUnchecked() call shouldn't be a cache miss; verified below

      }
    }
  }

  public void fetch(HttpUrl url) throws IOException {
    // Skip hosts that we've visited many times.
    AtomicInteger hostnameCount = new AtomicInteger();
    AtomicInteger previous = hostnames.putIfAbsent(url.host(), hostnameCount);
    if (previous != null) hostnameCount = previous;
    if (hostnameCount.incrementAndGet() > 100) return;

    Request request = new Request.Builder()
        .url(url)
        .build();

                for (Dependency dependency : source.getDependencies()) {
                    String key = dependency.getManagementKey();
                    Dependency present = dependencies.putIfAbsent(key, dependency);
                    if (present != null && !equals(dependency, present) && !directDependencies.contains(key)) {
                        // TODO: https://issues.apache.org/jira/browse/MNG-8004

            E result = (E) canonical;
            return result;
          }
        }

        // didn't see it, trying to put it instead...
        Dummy sneaky = map.putIfAbsent(sample, Dummy.VALUE);
        if (sneaky == null) {
          return sample;
        } else {
          /* Someone beat us to it! Trying again...
           *

        destroyProcess(sessionId);
        JobProcess jobProcess;
        try {
            jobProcess = new JobProcess(pb.start(), bufferSize, outputCallback);
            destroyProcess(sessionId, runningProcessMap.putIfAbsent(sessionId, jobProcess));
            return jobProcess;
        } catch (final IOException e) {
            throw new JobProcessingException("Crawler Process terminated.", e);
        }
    }

    }

    private final ConcurrentHashMap<TransferResourceIdentifier, Boolean> ongoing = new ConcurrentHashMap<>();

    @Override
    public void transferInitiated(TransferEvent event) {
        ongoing.putIfAbsent(new TransferResourceIdentifier(event.getResource()), Boolean.TRUE);
        put(event, false);
    }

    @Override
    public void transferStarted(TransferEvent event) throws TransferCancelledException {

            E result = (E) canonical;
            return result;
          }
        }

        // didn't see it, trying to put it instead...
        Dummy sneaky = map.putIfAbsent(sample, Dummy.VALUE);
        if (sneaky == null) {
          return sample;
        } else {
          /* Someone beat us to it! Trying again...
           *

        QueueHolder queueHolder = sessionCache.get(sessionId);
        if (queueHolder == null) {
            queueHolder = new QueueHolder();
            final QueueHolder prevQueueHolder = sessionCache.putIfAbsent(sessionId, queueHolder);
            return prevQueueHolder == null ? queueHolder : prevQueueHolder;
        }
        return queueHolder;
    }

    protected static class QueueHolder {