Dummy sneaky = map.putIfAbsent(sample, Dummy.VALUE);
        if (sneaky == null) {
          return sample;
        } else {
          /* Someone beat us to it! Trying again...
           *
           * Technically this loop not guaranteed to terminate, so theoretically (extremely
           * unlikely) this thread might starve, but even then, there is always going to be another

   * {@code next}. Once the implementation either invokes {@code endOfData} or throws an exception,
   * {@code computeNext} is guaranteed to never be called again.
   *
   * <p>If this method throws an exception, it will propagate outward to the {@code hasNext} or
   * {@code next} invocation that invoked this method. Any further attempts to use the iterator will

     *   available.
     * 3. We expect the client's get() to throw an InterruptedException.
     * 4. We expect the client thread's interrupt state to be false.
     * 5. The client thread again makes a blocking call to get().
     * 6. Now the result becomes available.
     * 7. We expect get() to return this result.
     * 8. We expect the test thread's interrupt state to be false.
     */

    return snapshot().toArray(array);
  }

  /*
   * We'd love to use 'new ArrayList(this)' or 'list.addAll(this)', but
   * either of these would recurse back to us again!
   */
  private List<E> snapshot() {
    List<E> list = Lists.newArrayListWithExpectedSize(size());
    for (Multiset.Entry<E> entry : entrySet()) {
      E element = entry.getElement();

   * {@code maximumSize / concurrencyLevel}.
   *
   * <p>When eviction is necessary, the cache evicts entries that are less likely to be used again.
   * For example, the cache may evict an entry because it hasn't been used recently or very often.
   *
   * <p>If {@code maximumSize} is zero, elements will be evicted immediately after being loaded into

    assertEquals(1, service.numIterations.get());
    service.stopAsync();
    service.secondBarrier.await();
    service.awaitTerminated();
    // Sleep for a while just to ensure that our task wasn't called again.
    Thread.sleep(UNIT.toMillis(3 * DELAY));
    assertEquals(1, service.numIterations.get());
  }

  public void testCustomScheduler_deadlock() throws InterruptedException, BrokenBarrierException {

 * whenever there is a chance the check may fail "in real life". Example:
 *
 * <pre>{@code
 * Bill bill = remoteService.getLastUnpaidBill();
 *
 * // In case bug 12345 happens again we'd rather just die
 * Verify.verify(bill.status() == Status.UNPAID,
 *     "Unexpected bill status: %s", bill.status());
 * }</pre>
 *
 * <h3>Comparison to alternatives</h3>
 *

                  // transitioned to a failed state, also this means that shutDown has already
                  // been called, so we do not want to call it again.
                  return;
                }
                shutDown();
              } finally {
                lock.unlock();
              }
              notifyStopped();

      L created = supplier.get();
      ArrayReference<L> newRef = new ArrayReference<>(created, index, queue);
      while (!locks.compareAndSet(index, existingRef, newRef)) {
        // we raced, we need to re-read and try again
        existingRef = locks.get(index);
        existing = existingRef == null ? null : existingRef.get();
        if (existing != null) {
          return existing;
        }
      }
      drainQueue();

     * manifest entry is already in {@code scannedFiles}, either because it was scanned earlier, or
     * it was intentionally added to the set by the caller, it will not be scanned again.
     *
     * <p>Note that when you call {@code location.scanResources(scannedFiles)}, the location will
     * always be scanned even if {@code scannedFiles} already contains it.
     */