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Contains com.google.common.util.concurrent.internal.InternalFutureFailureAccess and InternalFutures. Most users will never need to use this artifact. Its classes are conceptually a part of Guava, but they're in this separate artifact so that Android libraries can use them without pulling in all of Guava (just as they can use ListenableFuture by depending on the listenablefuture artifact).

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/*
 * Copyright (C) 2018 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.util.concurrent.internal;

/**
 * A future that, if it fails, may optionally provide access to the cause of the failure.
 *
 * This class is used only for micro-optimization. Standard {@code Future} utilities benefit from
 * this optimization, so there is no need to specialize methods to return or accept this type
 * instead of {@code ListenableFuture}.
 *
 * 
This class is GWT-compatible.
 *
 * @since {@code com.google.guava:failureaccess:1.0}, which was added as a dependency of Guava in
 *     Guava 27.0
 */
public abstract class InternalFutureFailureAccess {
  /** Constructor for use by subclasses. */
  protected InternalFutureFailureAccess() {}

  /**
   * Usually returns {@code null} but, if this {@code Future} has failed, may optionally
   * return the cause of the failure. "Failure" means specifically "completed with an exception"; it
   * does not include "was cancelled." To be explicit: If this method returns a non-null value,
   * then:
   *
   * 

   *   {@code isDone()} must return {@code true}
   *   
{@code isCancelled()} must return {@code false}
   *   
{@code get()} must not block, and it must throw an {@code ExecutionException} with the
   *       return value of this method as its cause
   * 
   *
   * This method is {@code protected} so that classes like {@code
   * com.google.common.util.concurrent.SettableFuture} do not expose it to their users as an
   * instance method. In the unlikely event that you need to call this method, call {@link
   * InternalFutures#tryInternalFastPathGetFailure(InternalFutureFailureAccess)}.
   */
  protected abstract Throwable tryInternalFastPathGetFailure();
}