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// Copyright 2018 The Bazel Authors. All rights reserved.
//
// 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.devtools.build.lib.skyframe.serialization;
import com.google.common.base.Preconditions;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.protobuf.ByteString;
import javax.annotation.Nullable;
/**
* A container class that holds an {@link #object} of type {@link T} and a possibly null {@link
* ListenableFuture}. If the {@link ListenableFuture} returned by {@link #getFutureToBlockWritesOn}
* is non-null, then, if {@link #object} is the serialized representation of some Bazel object, then
* it should not be written anywhere until the {@link ListenableFuture} in {@link
* #getFutureToBlockWritesOn} completes successfully.
*
* @param <T> Some serialized representation of an object, for instance a {@code byte[]} or a {@link
* ByteString}.
*/
public abstract class SerializationResult<T> {
private final T object;
private SerializationResult(T object) {
this.object = object;
}
/**
* Returns a new {@link SerializationResult} with the same future (if any) and {@code newObj}
* replacing the current {@link #getObject}.
*/
public abstract <S> SerializationResult<S> with(S newObj);
/**
* Returns a {@link ListenableFuture} that, if not null, must complete successfully before {@link
* #getObject} can be written remotely.
*/
@Nullable
public abstract ListenableFuture<Void> getFutureToBlockWritesOn();
/** Returns the stored object that should not be written remotely before the future completes. */
public T getObject() {
return object;
}
static <T> SerializationResult<T> create(
T object, @Nullable ListenableFuture<Void> futureToBlockWritesOn) {
return futureToBlockWritesOn != null
? new ObjectWithFuture<>(object, futureToBlockWritesOn)
: createWithoutFuture(object);
}
/** Creates an {@link SerializationResult} with a null future (no waiting necessary. */
public static <T> SerializationResult<T> createWithoutFuture(T object) {
return new ObjectWithoutFuture<>(object);
}
private static class ObjectWithoutFuture<T> extends SerializationResult<T> {
ObjectWithoutFuture(T obj) {
super(obj);
}
@Override
public <S> SerializationResult<S> with(S newObj) {
return new ObjectWithoutFuture<>(newObj);
}
@Override
public ListenableFuture<Void> getFutureToBlockWritesOn() {
return null;
}
}
private static class ObjectWithFuture<T> extends SerializationResult<T> {
private final ListenableFuture<Void> futureToBlockWritesOn;
ObjectWithFuture(T obj, @Nullable ListenableFuture<Void> futureToBlockWritesOn) {
super(obj);
this.futureToBlockWritesOn = Preconditions.checkNotNull(futureToBlockWritesOn, obj);
}
@Override
public <S> SerializationResult<S> with(S newObj) {
return new ObjectWithFuture<>(newObj, futureToBlockWritesOn);
}
@Override
public ListenableFuture<Void> getFutureToBlockWritesOn() {
return futureToBlockWritesOn;
}
}
}
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