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// Copyright 2016 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.exec.apple;
import com.google.common.base.Joiner;
import com.google.common.base.Preconditions;
import com.google.common.base.Splitter;
import com.google.common.collect.ImmutableList;
import com.google.devtools.build.lib.vfs.FileSystemUtils;
import com.google.devtools.build.lib.vfs.Path;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.List;
import javax.annotation.Nullable;
/**
* General cache file manager for mapping one or more keys to host-related path information.
*
* <p> Cache management has some notable restrictions:
* <ul>
* <li>Each cache entry must have the same number of (string) keys, and one value.</li>
* <li>An entry, once written to the cache, must be stable between builds. Clearing the cache
* requires a full clean of the bazel output directory.</li>
* </ul>
*
* <p> Note that a single cache manager instance is not thread-safe, though multiple threads may
* hold cache manager instances for the same cache file. As a result, it is possible multiple
* threads may write the same entry to cache. This is fine, as retrieval from the cache will simply
* return the first found entry.
*/
final class CacheManager {
private final Path cacheFilePath;
private boolean cacheFileTouched;
/**
* @param outputRoot path to the bazel's output root
* @param cacheFilename name of the cache file
*/
CacheManager(Path outputRoot, String cacheFilename) {
cacheFilePath = outputRoot.getRelative(cacheFilename);
}
private void touchCacheFile() throws IOException {
if (!cacheFileTouched) {
FileSystemUtils.touchFile(cacheFilePath);
cacheFileTouched = true;
}
}
/**
* Returns the value associated with the given list of string keys from the cache,
* or null if the entry is not present in the cache. If there is more than one value for the
* given key, the first value is returned.
*/
@Nullable
public String getValue(String... keys) throws IOException {
Preconditions.checkArgument(keys.length > 0);
touchCacheFile();
List<String> keyList = ImmutableList.copyOf(keys);
Iterable<String> cacheContents =
FileSystemUtils.readLines(cacheFilePath, StandardCharsets.UTF_8);
for (String cacheLine : cacheContents) {
if (cacheLine.isEmpty()) {
continue;
}
List<String> cacheEntry = Splitter.on(':').splitToList(cacheLine);
List<String> cacheKeys = cacheEntry.subList(0, cacheEntry.size() - 1);
String cacheValue = cacheEntry.get(cacheEntry.size() - 1);
if (keyList.size() != cacheKeys.size()) {
throw new IllegalStateException(
String.format("cache file %s is malformed. Expected %s keys. line: '%s'",
cacheFilePath, keyList.size(), cacheLine));
}
if (keyList.equals(cacheKeys)) {
return cacheValue;
}
}
return null;
}
/**
* Write an entry to the cache. An entry consists of one or more keys and a single value.
* No validation is made regarding whether there are redundant or conflicting entries in the
* cache; it is thus the responsibility of the caller to ensure that any redundant entries
* (entries which have the same keys) also have the same value.
*/
public void writeEntry(List<String> keys, String value) throws IOException {
Preconditions.checkArgument(!keys.isEmpty());
touchCacheFile();
FileSystemUtils.appendLinesAs(cacheFilePath, StandardCharsets.UTF_8,
Joiner.on(":").join(ImmutableList.builder().addAll(keys).add(value).build()));
}
}
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