| /* |
| * 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 <i>optionally</i> provide access to the cause of the failure. |
| * |
| * <p>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}. |
| * |
| * <p>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 <i>optionally</i> |
| * 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: |
| * |
| * <ul> |
| * <li>{@code isDone()} must return {@code true} |
| * <li>{@code isCancelled()} must return {@code false} |
| * <li>{@code get()} must not block, and it must throw an {@code ExecutionException} with the |
| * return value of this method as its cause |
| * </ul> |
| * |
| * <p>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(); |
| } |