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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.analysis.config;
import com.google.common.collect.ImmutableSortedSet;
import com.google.common.collect.Interner;
import com.google.devtools.build.lib.concurrent.BlazeInterners;
import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
import com.google.devtools.build.lib.util.Fingerprint;
import java.util.Arrays;
import javax.annotation.Nullable;
/**
* A wrapper class for an {@code ImmutableSortedSet<Class<? extends BuildConfiguration.Fragment>>}
* object. Interning these objects allows us to do cheap reference equality checks when these sets
* are in frequently used keys. For good measure, we also compute a fingerprint.
*/
@AutoCodec
public class FragmentClassSet {
private final ImmutableSortedSet<Class<? extends BuildConfiguration.Fragment>> fragments;
// Lazily initialized.
@Nullable private volatile byte[] fingerprint;
private volatile int hashCode;
private FragmentClassSet(
ImmutableSortedSet<Class<? extends BuildConfiguration.Fragment>> fragments) {
this.fragments = fragments;
}
private static final Interner<FragmentClassSet> interner = BlazeInterners.newWeakInterner();
@AutoCodec.Instantiator
public static FragmentClassSet of(
ImmutableSortedSet<Class<? extends BuildConfiguration.Fragment>> fragments) {
return interner.intern(new FragmentClassSet(fragments));
}
public ImmutableSortedSet<Class<? extends BuildConfiguration.Fragment>> fragmentClasses() {
return fragments;
}
/**
* Lazily initialize {@link #fingerprint} and {@link #hashCode}. Keeps computation off critical
* path of build, while still avoiding expensive computation for equality and hash code each time.
*
* <p>We check for nullity of {@link #fingerprint} to see if this method has already been called.
* Using {@link #hashCode} after this method is called is safe because it is set here before
* {@link #fingerprint} is set, so if {@link #fingerprint} is non-null then {@link #hashCode} is
* definitely set.
*/
private void maybeInitializeFingerprintAndHashCode() {
if (fingerprint != null) {
return;
}
synchronized (this) {
if (fingerprint != null) {
return;
}
Fingerprint fingerprint = new Fingerprint();
for (Class<? extends BuildConfiguration.Fragment> fragment : fragments) {
fingerprint.addString(fragment.getName());
}
byte[] computedFingerprint = fingerprint.digestAndReset();
hashCode = Arrays.hashCode(computedFingerprint);
this.fingerprint = computedFingerprint;
}
}
@Override
public boolean equals(Object other) {
if (this == other) {
return true;
} else if (!(other instanceof FragmentClassSet)) {
return false;
} else {
maybeInitializeFingerprintAndHashCode();
FragmentClassSet that = (FragmentClassSet) other;
that.maybeInitializeFingerprintAndHashCode();
return Arrays.equals(this.fingerprint, that.fingerprint);
}
}
@Override
public int hashCode() {
maybeInitializeFingerprintAndHashCode();
return hashCode;
}
}
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