| // 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())); |
| } |
| } |