src/main/java/com/google/devtools/build/lib/remote/MemcacheActionCache.java

// 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.remote;

import com.google.common.hash.HashCode;
import com.google.devtools.build.lib.actions.ActionInput;
import com.google.devtools.build.lib.actions.ActionInputFileCache;
import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
import com.google.devtools.build.lib.remote.RemoteProtocol.CacheEntry;
import com.google.devtools.build.lib.remote.RemoteProtocol.FileEntry;
import com.google.devtools.build.lib.util.Preconditions;
import com.google.devtools.build.lib.vfs.Path;
import com.google.protobuf.ByteString;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Collection;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.Semaphore;

/**
 * A RemoteActionCache implementation that uses memcache as a distributed storage
 * for files and action output. The memcache is accessed by the {@link ConcurrentMap}
 * interface.
 *
 * The thread satefy is guaranteed by the underlying memcache client.
 */
@ThreadSafe
final class MemcacheActionCache implements RemoteActionCache {
  private final Path execRoot;
  private final ConcurrentMap<String, byte[]> cache;
  private static final int MAX_MEMORY_KBYTES = 512 * 1024;
  private final Semaphore uploadMemoryAvailable = new Semaphore(MAX_MEMORY_KBYTES, true);

  /**
   * Construct an action cache using JCache API.
   */
  MemcacheActionCache(
      Path execRoot, RemoteOptions options, ConcurrentMap<String, byte[]> cache) {
    this.execRoot = execRoot;
    this.cache = cache;
  }

  @Override
  public String putFileIfNotExist(Path file) throws IOException {
    String contentKey = HashCode.fromBytes(file.getMD5Digest()).toString();
    if (containsFile(contentKey)) {
      return contentKey;
    }
    putFile(contentKey, file);
    return contentKey;
  }

  @Override
  public String putFileIfNotExist(ActionInputFileCache cache, ActionInput file) throws IOException {
    // PerActionFileCache already converted this to a lowercase ascii string.. it's not consistent!
    String contentKey = new String(cache.getDigest(file).toByteArray());
    if (containsFile(contentKey)) {
      return contentKey;
    }
    putFile(contentKey, execRoot.getRelative(file.getExecPathString()));
    return contentKey;
  }

  private void putFile(String key, Path file) throws IOException {
    int fileSizeKBytes = (int) (file.getFileSize() / 1024);
    Preconditions.checkArgument(fileSizeKBytes < MAX_MEMORY_KBYTES);
    try {
      uploadMemoryAvailable.acquire(fileSizeKBytes);
      // TODO(alpha): I should put the file content as chunks to avoid reading the entire
      // file into memory.
      try (InputStream stream = file.getInputStream()) {
        cache.put(
            key,
            CacheEntry.newBuilder()
                .setFileContent(ByteString.readFrom(stream))
                .build()
                .toByteArray());
      }
    } catch (InterruptedException e) {
      throw new IOException("Failed to put file to memory cache.", e);
    } finally {
      uploadMemoryAvailable.release(fileSizeKBytes);
    }
  }

  @Override
  public void writeFile(String key, Path dest, boolean executable)
      throws IOException, CacheNotFoundException {
    byte[] data = cache.get(key);
    if (data == null) {
      throw new CacheNotFoundException("File content cannot be found with key: " + key);
    }
    try (OutputStream stream = dest.getOutputStream()) {
      CacheEntry.parseFrom(data).getFileContent().writeTo(stream);
      dest.setExecutable(executable);
    }
  }

  private boolean containsFile(String key) {
    return cache.containsKey(key);
  }

  @Override
  public void writeActionOutput(String key, Path execRoot)
      throws IOException, CacheNotFoundException {
    byte[] data = cache.get(key);
    if (data == null) {
      throw new CacheNotFoundException("Action output cannot be found with key: " + key);
    }
    CacheEntry cacheEntry = CacheEntry.parseFrom(data);
    for (FileEntry file : cacheEntry.getFilesList()) {
      writeFile(file.getContentKey(), execRoot.getRelative(file.getPath()), file.getExecutable());
    }
  }

  @Override
  public void putActionOutput(String key, Collection<? extends ActionInput> outputs)
      throws IOException {
    CacheEntry.Builder actionOutput = CacheEntry.newBuilder();
    for (ActionInput output : outputs) {
      Path file = execRoot.getRelative(output.getExecPathString());
      addToActionOutput(file, output.getExecPathString(), actionOutput);
    }
    cache.put(key, actionOutput.build().toByteArray());
  }

  @Override
  public void putActionOutput(String key, Path execRoot, Collection<Path> files)
      throws IOException {
    CacheEntry.Builder actionOutput = CacheEntry.newBuilder();
    for (Path file : files) {
      addToActionOutput(file, file.relativeTo(execRoot).getPathString(), actionOutput);
    }
    cache.put(key, actionOutput.build().toByteArray());
  }

  /**
   * Add the file to action output cache entry. Put the file to cache if necessary.
   */
  private void addToActionOutput(Path file, String execPathString, CacheEntry.Builder actionOutput)
      throws IOException {
    if (file.isDirectory()) {
      // TODO(alpha): Implement this for directory.
      throw new UnsupportedOperationException("Storing a directory is not yet supported.");
    }
    // First put the file content to cache.
    String contentKey = putFileIfNotExist(file);
    // Add to protobuf.
    actionOutput
        .addFilesBuilder()
        .setPath(execPathString)
        .setContentKey(contentKey)
        .setExecutable(file.isExecutable());
  }
}