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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.Deserializer;
import com.google.devtools.build.lib.skyframe.serialization.ObjectCodecRegistry.CodecDescriptor;
import com.google.protobuf.CodedInputStream;
import java.io.IOException;
import javax.annotation.CheckReturnValue;
/**
* Stateful class for providing additional context to a single deserialization "session". This class
* is thread-safe so long as {@link #deserializer} is null. If it is not null, this class is not
* thread-safe and should only be accessed on a single thread for deserializing one serialized
* object (that may contain other serialized objects inside it).
*/
public class DeserializationContext {
private final ObjectCodecRegistry registry;
private final ImmutableMap<Class<?>, Object> dependencies;
private final Memoizer.Deserializer deserializer;
private DeserializationContext(
ObjectCodecRegistry registry,
ImmutableMap<Class<?>, Object> dependencies,
Deserializer deserializer) {
this.registry = registry;
this.dependencies = dependencies;
this.deserializer = deserializer;
}
@VisibleForTesting
public DeserializationContext(
ObjectCodecRegistry registry, ImmutableMap<Class<?>, Object> dependencies) {
this(registry, dependencies, /*deserializer=*/ null);
}
@VisibleForTesting
public DeserializationContext(ImmutableMap<Class<?>, Object> dependencies) {
this(AutoRegistry.get(), dependencies);
}
// TODO(shahan): consider making codedIn a member of this class.
@SuppressWarnings({"TypeParameterUnusedInFormals", "unchecked"})
public <T> T deserialize(CodedInputStream codedIn) throws IOException, SerializationException {
int tag = codedIn.readSInt32();
if (tag == 0) {
return null;
}
if (tag < 0) {
// Subtract 1 to undo transformation from SerializationContext to avoid null.
return (T) deserializer.getMemoized(-tag - 1);
}
T constant = (T) registry.maybeGetConstantByTag(tag);
if (constant != null) {
return constant;
}
CodecDescriptor codecDescriptor = registry.getCodecDescriptorByTag(tag);
if (deserializer == null) {
return (T) codecDescriptor.deserialize(this, codedIn);
} else {
return deserializer.deserialize(this, (ObjectCodec<T>) codecDescriptor.getCodec(), codedIn);
}
}
/**
* Register an initial value for the currently deserializing value, for use by child objects that
* may have references to it.
*
* <p>This is a noop when memoization is disabled.
*/
public <T> void registerInitialValue(T initialValue) {
if (deserializer == null) {
return;
}
deserializer.registerInitialValue(initialValue);
}
@SuppressWarnings("unchecked")
public <T> T getDependency(Class<T> type) {
Preconditions.checkNotNull(type);
return (T) dependencies.get(type);
}
/**
* Returns a {@link DeserializationContext} that will memoize values it encounters (using
* reference equality), the inverse of the memoization performed by a {@link SerializationContext}
* returned by {@link SerializationContext#getMemoizingContext}. The context returned here should
* be used instead of the original: memoization may only occur when using the returned context.
*
* <p>This method is idempotent: calling it on an already memoizing context will return the same
* context.
*/
@CheckReturnValue
public DeserializationContext getMemoizingContext() {
if (deserializer != null) {
return this;
}
return getNewMemoizingContext();
}
/**
* Returns a memoizing {@link DeserializationContext}, as getMemoizingContext above. Unlike
* getMemoizingContext, this method is not idempotent - the returned context will always be fresh.
*/
public DeserializationContext getNewMemoizingContext() {
return new DeserializationContext(this.registry, this.dependencies, new Deserializer());
}
public DeserializationContext getNewNonMemoizingContext() {
return new DeserializationContext(this.registry, this.dependencies, null);
}
}
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