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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.skyframe;
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;
import com.google.devtools.build.lib.vfs.RootedPath;
import com.google.devtools.build.skyframe.SkyKey;
import com.google.devtools.build.skyframe.SkyValue;
/**
* A value for ensuring that a file symlink cycle is reported exactly once. This is achieved by
* forcing the same value key for two logically equivalent cycles (e.g. ['a' -> 'b' -> 'c' -> 'a']
* and ['b' -> 'c' -> 'a' -> 'b'], and letting Skyframe do its magic.
*/
class FileSymlinkCycleUniquenessValue implements SkyValue {
public static final FileSymlinkCycleUniquenessValue INSTANCE =
new FileSymlinkCycleUniquenessValue();
private FileSymlinkCycleUniquenessValue() {
}
static SkyKey key(ImmutableList<RootedPath> cycle) {
Preconditions.checkState(!cycle.isEmpty());
return new SkyKey(SkyFunctions.FILE_SYMLINK_CYCLE_UNIQUENESS, canonicalize(cycle));
}
private static ImmutableList<RootedPath> canonicalize(ImmutableList<RootedPath> cycle) {
int minPos = 0;
String minString = cycle.get(0).toString();
for (int i = 1; i < cycle.size(); i++) {
String candidateString = cycle.get(i).toString();
if (candidateString.compareTo(minString) < 0) {
minPos = i;
minString = candidateString;
}
}
ImmutableList.Builder<RootedPath> builder = ImmutableList.builder();
for (int i = 0; i < cycle.size(); i++) {
int pos = (minPos + i) % cycle.size();
builder.add(cycle.get(pos));
}
return builder.build();
}
}
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