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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.skyframe;
import static com.google.common.base.Preconditions.checkNotNull;
/**
* For use when the {@link #argument} of the {@link SkyKey} cannot be a {@link SkyKey} itself,
* either because it is a type like List or because it is already a different {@link SkyKey}.
* Provides convenient boilerplate.
*
* <p>An argument's hash code might not be stable across JVM instances if it transitively depends on
* an object that uses the default identity-based {@link Object#hashCode} or {@link
* System#identityHashCode}. For this reason, the {@link #hashCode} field is {@code transient}.
* Subclasses should manage serialization (i.e. using {@code AutoCodec}) to ensure that {@link
* #AbstractSkyKey(Object)} is invoked on deserialization to freshly compute the hash code.
*/
public abstract class AbstractSkyKey<T> implements SkyKey {
// Visible for serialization.
protected final T arg;
/**
* Caches the hash code for this object. It might be expensive to compute.
*
* <p>The hash code is computed eagerly because it is expected that instances are interned,
* meaning that {@link #hashCode()} will be called immediately for every instance.
*/
private final transient int hashCode;
protected AbstractSkyKey(T arg) {
this.arg = checkNotNull(arg);
this.hashCode = 31 * functionName().hashCode() + arg.hashCode();
}
@Override
public final int hashCode() {
return hashCode;
}
@Override
public final T argument() {
return arg;
}
@Override
public final boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null || getClass() != obj.getClass()) {
return false;
}
AbstractSkyKey<?> that = (AbstractSkyKey<?>) obj;
return hashCode == that.hashCode
&& functionName().equals(that.functionName())
&& arg.equals(that.arg);
}
@Override
public String toString() {
return functionName() + ":" + arg;
}
}