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// Copyright 2017 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.collect.nestedset;
import com.google.devtools.build.lib.util.Fingerprint;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
/** Computes fingerprints for nested sets, reusing sub-computations from children. */
public abstract class NestedSetFingerprintCache<T> {
private static final byte[] EMPTY_SET_BYTES = new byte[] {};
private Map<Object, byte[]> fingerprints = createMap();
public void addNestedSetToFingerprint(Fingerprint fingerprint, NestedSet<T> nestedSet) {
fingerprint.addInt(nestedSet.getOrder().ordinal());
Object children = nestedSet.rawChildren();
byte[] bytes = getBytes(children);
fingerprint.addBytes(bytes);
}
public void clear() {
fingerprints = createMap();
}
private byte[] getBytes(Object children) {
byte[] bytes = fingerprints.get(children);
if (bytes == null) {
if (children instanceof Object[]) {
Fingerprint fingerprint = new Fingerprint();
for (Object child : (Object[]) children) {
if (child instanceof Object[]) {
fingerprint.addBytes(getBytes(child));
} else {
addItemFingerprint(fingerprint, cast(child));
}
}
bytes = fingerprint.digestAndReset();
// There is no point memoizing anything except the multi-item case,
// since the single-item case gets inlined into its parents anyway,
// and the empty set is a singleton
fingerprints.put(children, bytes);
} else if (children != NestedSet.EMPTY_CHILDREN) {
// Single item
Fingerprint fingerprint = new Fingerprint();
addItemFingerprint(fingerprint, cast(children));
bytes = fingerprint.digestAndReset();
} else {
// Empty nested set
bytes = EMPTY_SET_BYTES;
}
}
return bytes;
}
@SuppressWarnings("unchecked")
private T cast(Object item) {
return (T) item;
}
private static Map<Object, byte[]> createMap() {
return new ConcurrentHashMap<>();
}
protected abstract void addItemFingerprint(Fingerprint fingerprint, T item);
}
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