* <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/ListenableFutureExplained">{@code
 * ListenableFuture}</a>.
 *
 * <p>This class is GWT-compatible.
 *
 * <h3>Purpose</h3>
 *
 * <p>The main purpose of {@code ListenableFuture} is to help you chain together a graph of
 * asynchronous operations. You can chain them together manually with calls to methods like {@link

  SUPPORTS_ADD,
  SUPPORTS_REMOVE,
  SUPPORTS_ITERATOR_REMOVE,
  FAILS_FAST_ON_CONCURRENT_MODIFICATION,

  /**
   * Features supported by general-purpose collections - everything but {@link #RESTRICTS_ELEMENTS}.
   *
   * @see java.util.Collection the definition of general-purpose collections.
   */
  GENERAL_PURPOSE(SUPPORTS_ADD, SUPPORTS_REMOVE, SUPPORTS_ITERATOR_REMOVE),

 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/ListenableFutureExplained">{@code
 * ListenableFuture}</a>.
 *
 * <p>This class is GWT-compatible.
 *
 * <h3>Purpose</h3>
 *
 * <p>The main purpose of {@code ListenableFuture} is to help you chain together a graph of
 * asynchronous operations. You can chain them together manually with calls to methods like {@link

 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/ListenableFutureExplained">{@code
 * ListenableFuture}</a>.
 *
 * <p>This class is GWT-compatible.
 *
 * <h3>Purpose</h3>
 *
 * <p>The main purpose of {@code ListenableFuture} is to help you chain together a graph of
 * asynchronous operations. You can chain them together manually with calls to methods like {@link

 * recommended that the caller does not persist a reference to the backing map (unless the backing
 * map is immutable).
 *
 * <p>This class is tailored toward use cases in common.graph. It is *NOT* a general purpose map.
 *
 * @author James Sexton
 */
class MapIteratorCache<K, V> {
  private final Map<K, V> backingMap;

  /*
   * Per JDK: "the behavior of a map entry is undefined if the backing map has been modified after

      the copyright owner. For the purposes of this definition, "submitted"
      means any form of electronic, verbal, or written communication sent
      to the Licensor or its representatives, including but not limited to
      communication on electronic mailing lists, source code control systems,
      and issue tracking systems that are managed by, or on behalf of, the
      Licensor for the purpose of discussing and improving the Work, but

      the copyright owner. For the purposes of this definition, "submitted"
      means any form of electronic, verbal, or written communication sent
      to the Licensor or its representatives, including but not limited to
      communication on electronic mailing lists, source code control systems,
      and issue tracking systems that are managed by, or on behalf of, the
      Licensor for the purpose of discussing and improving the Work, but

all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

  SUPPORTS_ADD,
  SUPPORTS_REMOVE,
  SUPPORTS_ITERATOR_REMOVE,
  FAILS_FAST_ON_CONCURRENT_MODIFICATION,

  /**
   * Features supported by general-purpose collections - everything but {@link #RESTRICTS_ELEMENTS}.
   *
   * @see java.util.Collection the definition of general-purpose collections.
   */
  GENERAL_PURPOSE(SUPPORTS_ADD, SUPPORTS_REMOVE, SUPPORTS_ITERATOR_REMOVE),

copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,