// simplest instance, though very similar descriptions apply to many other classes in this file.
  //
  // In the constructor of AbstractCatchingFuture, the delegate future is assigned to a field
  // 'inputFuture'. That field is non-final and non-volatile. There are 2 places where the
  // 'inputFuture' field is read and where we will have to consider visibility of the write
  // operation in the constructor.
  //

                    try {
                      peeker.getDone(input2Failed);
                      fail("Peeker.getDone() should fail for failed inputs");
                    } catch (ExecutionException expected) {
                    }
                    try {
                      peeker.getDone(nonInput);
                      fail("Peeker should not be able to peek into non-input ClosingFuture.");

                    try {
                      peeker.getDone(input2Failed);
                      fail("Peeker.getDone() should fail for failed inputs");
                    } catch (ExecutionException expected) {
                    }
                    try {
                      peeker.getDone(nonInput);
                      fail("Peeker should not be able to peek into non-input ClosingFuture.");

  /**
   * Returns an iterator that cycles indefinitely over the elements of {@code iterable}.
   *
   * <p>The returned iterator supports {@code remove()} if the provided iterator does. After {@code
   * remove()} is called, subsequent cycles omit the removed element, which is no longer in {@code
   * iterable}. The iterator's {@code hasNext()} method returns {@code true} until {@code iterable}
   * is empty.
   *

  // available.
  /**
   * This field encodes the current state of the future.
   *
   * <p>The valid values are:
   *
   * <ul>
   *   <li>{@code null} initial state, nothing has happened.
   *   <li>{@link Cancellation} terminal state, {@code cancel} was called.
   *   <li>{@link Failure} terminal state, {@code setException} was called.

    try {
      cache.getUnchecked("bar");
      fail();
    } catch (InvalidCacheLoadException expected) {
    }
    assertEquals(2, callCount.get());
  }

  /**
   * On a concurrent computation that throws an unchecked exception, all threads should get the
   * (wrapped) exception, with the loader called only once. The result should not be cached (a later

                // requireNonNull is safe because the first `size` elements have been filled in.
                requireNonNull(e1);
                requireNonNull(e2);
                return comparator.compare(e1.getKey(), e2.getKey());
              });
          // requireNonNull is safe because the first `size` elements have been filled in.
          Entry<K, V> firstEntry = requireNonNull(entryArray[0]);

 * }</pre>
 *
 * <p>so that a hypothetical bad caller of this method, such as:
 *
 * <pre>{@code
 * void exampleBadCaller() {
 *   double d = sqrt(-1.0);
 * }
 * }</pre>
 *
 * <p>would be flagged as having called {@code sqrt()} with an illegal argument.
 *
 * <h3>Performance</h3>
 *
 * <p>Avoid passing message arguments that are expensive to compute; your code will always compute

    try {
      cache.getUnchecked("bar");
      fail();
    } catch (InvalidCacheLoadException expected) {
    }
    assertEquals(2, callCount.get());
  }

  /**
   * On a concurrent computation that throws an unchecked exception, all threads should get the
   * (wrapped) exception, with the loader called only once. The result should not be cached (a later

                // requireNonNull is safe because the first `size` elements have been filled in.
                requireNonNull(e1);
                requireNonNull(e2);
                return comparator.compare(e1.getKey(), e2.getKey());
              });
          // requireNonNull is safe because the first `size` elements have been filled in.
          Entry<K, V> firstEntry = requireNonNull(entryArray[0]);