1 files changed, 143 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/exec/SingleBuildFileCache.java b/src/main/java/com/google/devtools/build/lib/exec/SingleBuildFileCache.java
new file mode 100644
index 0000000000..8ec1e51583
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/exec/SingleBuildFileCache.java
@@ -0,0 +1,143 @@
+// 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.exec;
+
+import static java.nio.charset.StandardCharsets.US_ASCII;
+
+import com.google.common.base.Preconditions;
+import com.google.common.cache.CacheBuilder;
+import com.google.common.cache.CacheLoader;
+import com.google.common.cache.LoadingCache;
+import com.google.common.collect.Maps;
+import com.google.common.io.BaseEncoding;
+import com.google.devtools.build.lib.actions.ActionInput;
+import com.google.devtools.build.lib.actions.ActionInputFileCache;
+import com.google.devtools.build.lib.actions.DigestOfDirectoryException;
+import com.google.devtools.build.lib.util.Pair;
+import com.google.devtools.build.lib.vfs.FileSystem;
+import com.google.devtools.build.lib.vfs.Path;
+import com.google.protobuf.ByteString;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.Map;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.ThreadSafe;
+
+/**
+ * An in-memory cache to ensure we do I/O for source files only once during a single build.
+ *
+ * <p>Simply maintains a two-way cached mapping from digest <--> filename that may be populated
+ * only once.
+ */
+@ThreadSafe
+public class SingleBuildFileCache implements ActionInputFileCache {
+
+  private final String cwd;
+  private final FileSystem fs;
+
+  public SingleBuildFileCache(String cwd, FileSystem fs) {
+    this.fs = Preconditions.checkNotNull(fs);
+    this.cwd = Preconditions.checkNotNull(cwd);
+  }
+
+  // If we can't get the digest, we store the exception. This avoids extra file IO for files
+  // that are allowed to be missing, as we first check a likely non-existent content file
+  // first.  Further we won't need to unwrap the exception in getDigest().
+  private final LoadingCache<ActionInput, Pair<ByteString, IOException>> pathToDigest =
+      CacheBuilder.newBuilder()
+      // We default to 10 disk read threads, but we don't expect them all to edit the map
+      // simultaneously.
+      .concurrencyLevel(8)
+      // Even small-ish builds, as of 11/21/2011 typically have over 10k artifacts, so it's
+      // unlikely that this default will adversely affect memory in most cases.
+      .initialCapacity(10000)
+      .build(new CacheLoader<ActionInput, Pair<ByteString, IOException>>() {
+        @Override
+        public Pair<ByteString, IOException> load(ActionInput input) {
+          Path path = null;
+          try {
+            path = fs.getPath(fullPath(input));
+            BaseEncoding hex = BaseEncoding.base16().lowerCase();
+            ByteString digest = ByteString.copyFrom(
+                hex.encode(path.getMD5Digest())
+                   .getBytes(US_ASCII));
+            pathToBytes.put(input, path.getFileSize());
+            // Inject reverse mapping. Doing this unconditionally in getDigest() showed up
+            // as a hotspot in CPU profiling.
+            digestToPath.put(digest, input);
+            return Pair.of(digest, null);
+          } catch (IOException e) {
+            if (path != null && path.isDirectory()) {
+              pathToBytes.put(input, 0L);
+              return Pair.<ByteString, IOException>of(null, new DigestOfDirectoryException(
+                  "Input is a directory: " + input.getExecPathString()));
+            }
+
+            // Put value into size map to avoid trying to read file again later.
+            pathToBytes.put(input, 0L);
+            return Pair.of(null, e);
+          }
+        }
+      });
+
+  private final Map<ByteString, ActionInput> digestToPath = Maps.newConcurrentMap();
+
+  private final Map<ActionInput, Long> pathToBytes = Maps.newConcurrentMap();
+
+  @Nullable
+  @Override
+  public File getFileFromDigest(ByteString digest) {
+    ActionInput relPath = digestToPath.get(digest);
+    return relPath == null ? null : new File(fullPath(relPath));
+  }
+
+  @Override
+  public long getSizeInBytes(ActionInput input) throws IOException {
+    // TODO(bazel-team): this only works if pathToDigest has already been called.
+    Long sz = pathToBytes.get(input);
+    if (sz != null) {
+      return sz;
+    }
+    Path path = fs.getPath(fullPath(input));
+    sz = path.getFileSize();
+    pathToBytes.put(input, sz);
+    return sz;
+  }
+
+  @Override
+  public ByteString getDigest(ActionInput input) throws IOException {
+    Pair<ByteString, IOException> result = pathToDigest.getUnchecked(input);
+    if (result.second != null) {
+      throw result.second;
+    }
+    return result.first;
+  }
+
+  @Override
+  public boolean contentsAvailableLocally(ByteString digest) {
+    return digestToPath.containsKey(digest);
+  }
+
+  /**
+   * Creates a File object that refers to fileName, if fileName is an absolute path. Otherwise,
+   * returns a File object that refers to the fileName appended to the (absolute) current working
+   * directory.
+   */
+  private String fullPath(ActionInput input) {
+    String relPath = input.getExecPathString();
+    return relPath.startsWith("/") ? relPath : new File(cwd, relPath).getPath();
+  }
+}