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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 <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();
}
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