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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.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableMap;
import com.google.devtools.build.lib.skyframe.serialization.Memoizer.Serializer;
import com.google.devtools.build.lib.skyframe.serialization.SerializationException.NoCodecException;
import com.google.protobuf.CodedOutputStream;
import java.io.IOException;
import javax.annotation.CheckReturnValue;
import javax.annotation.Nullable;
/**
* Stateful class for providing additional context to a single serialization "session". This class
* is thread-safe so long as {@link #serializer} is null. If it is not null, this class is not
* thread-safe and should only be accessed on a single thread for serializing one object (that may
* involve serializing other objects contained in it).
*/
public class SerializationContext {
private final ObjectCodecRegistry registry;
private final ImmutableMap<Class<?>, Object> dependencies;
@Nullable private final Memoizer.Serializer serializer;
private SerializationContext(
ObjectCodecRegistry registry,
ImmutableMap<Class<?>, Object> dependencies,
@Nullable Serializer serializer) {
this.registry = registry;
this.dependencies = dependencies;
this.serializer = serializer;
}
@VisibleForTesting
public SerializationContext(
ObjectCodecRegistry registry, ImmutableMap<Class<?>, Object> dependencies) {
this(registry, dependencies, /*serializer=*/ null);
}
@VisibleForTesting
public SerializationContext(ImmutableMap<Class<?>, Object> dependencies) {
this(AutoRegistry.get(), dependencies);
}
// TODO(shahan): consider making codedOut a member of this class.
public void serialize(Object object, CodedOutputStream codedOut)
throws IOException, SerializationException {
ObjectCodecRegistry.CodecDescriptor descriptor =
recordAndGetDescriptorIfNotConstantMemoizedOrNull(object, codedOut);
if (descriptor != null) {
if (serializer == null) {
descriptor.serialize(this, object, codedOut);
} else {
@SuppressWarnings("unchecked")
ObjectCodec<Object> castCodec = (ObjectCodec<Object>) descriptor.getCodec();
serializer.serialize(this, object, castCodec, codedOut);
}
}
}
@SuppressWarnings("unchecked")
public <T> T getDependency(Class<T> type) {
Preconditions.checkNotNull(type);
return (T) dependencies.get(type);
}
/**
* Returns a {@link SerializationContext} that will memoize values it encounters (using reference
* equality) in a new memoization table. The returned context should be used instead of the
* original: memoization may only occur when using the returned context. Calls must be in pairs
* with {@link DeserializationContext#getMemoizingContext} in the corresponding deserialization
* code.
*
* <p>This method is idempotent: calling it on an already memoizing context will return the same
* context.
*/
@CheckReturnValue
SerializationContext getMemoizingContext() {
if (serializer != null) {
return this;
}
return getNewMemoizingContext();
}
/**
* Returns a memoizing {@link SerializationContext}, as getMemoizingContext above. Unlike
* getMemoizingContext, this method is not idempotent - the returned context will always be fresh.
*/
public SerializationContext getNewMemoizingContext() {
return new SerializationContext(this.registry, this.dependencies, new Memoizer.Serializer());
}
private boolean writeNullOrConstant(@Nullable Object object, CodedOutputStream codedOut)
throws IOException {
if (object == null) {
codedOut.writeSInt32NoTag(0);
return true;
}
Integer tag = registry.maybeGetTagForConstant(object);
if (tag != null) {
codedOut.writeSInt32NoTag(tag);
return true;
}
return false;
}
@Nullable
private ObjectCodecRegistry.CodecDescriptor recordAndGetDescriptorIfNotConstantMemoizedOrNull(
@Nullable Object object, CodedOutputStream codedOut) throws IOException, NoCodecException {
if (writeNullOrConstant(object, codedOut)) {
return null;
}
if (serializer != null) {
Integer memoizedIndex = serializer.getMemoizedIndex(object);
if (memoizedIndex != null) {
// Subtract 1 so it will be negative and not collide with null.
codedOut.writeSInt32NoTag(-memoizedIndex - 1);
return null;
}
}
ObjectCodecRegistry.CodecDescriptor descriptor = registry.getCodecDescriptorForObject(object);
codedOut.writeSInt32NoTag(descriptor.getTag());
return descriptor;
}
}
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