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// Copyright 2014 Google Inc. 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.actions.cache;
import com.google.common.base.Preconditions;
import com.google.common.io.BaseEncoding;
import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
import java.util.Arrays;
import java.util.Date;
/**
* A class to represent file metadata.
* ActionCacheChecker may assume that, for a given file, equal
* metadata at different moments implies equal file-contents,
* where metadata equality is computed using Metadata.equals().
* <p>
* NB! Several other parts of Blaze are relying on the fact that metadata
* uses mtime and not ctime. If metadata is ever changed
* to use ctime, all uses of Metadata must be carefully examined.
*/
@Immutable @ThreadSafe
public final class Metadata {
public final long mtime;
public final byte[] digest;
// Convenience object for use with volatile files that we do not want checked
// (e.g. the build-changelist.txt)
public static final Metadata CONSTANT_METADATA = new Metadata(-1);
public Metadata(long mtime) {
this.mtime = mtime;
this.digest = null;
}
public Metadata(byte[] digest) {
this.mtime = 0L;
this.digest = Preconditions.checkNotNull(digest);
}
@Override
public int hashCode() {
int hash = 0;
if (digest != null) {
// We are already dealing with the digest so we can just use portion of it
// as a hash code.
hash += digest[0] + (digest[1] << 8) + (digest[2] << 16) + (digest[3] << 24);
} else {
// Inlined hashCode for Long, so we don't
// have to construct an Object, just to compute
// a 32-bit hash out of a 64 bit value.
hash = (int) (mtime ^ (mtime >>> 32));
}
return hash;
}
@Override
public boolean equals(Object that) {
if (this == that) {
return true;
}
if (!(that instanceof Metadata)) {
return false;
}
// Do a strict comparison - both digest and mtime should match
return Arrays.equals(this.digest, ((Metadata) that).digest)
&& this.mtime == ((Metadata) that).mtime;
}
@Override
public String toString() {
if (digest != null) {
return "MD5 " + BaseEncoding.base16().lowerCase().encode(digest);
} else if (mtime > 0) {
return "timestamp " + new Date(mtime);
}
return "no metadata";
}
}
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