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// Copyright 2014 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;
import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;
import com.google.devtools.build.lib.actions.ActionInput;
import com.google.devtools.build.lib.actions.Artifact;
import com.google.devtools.build.lib.actions.DigestOfDirectoryException;
import com.google.devtools.build.lib.actions.FileArtifactValue;
import com.google.devtools.build.lib.actions.MetadataProvider;
import com.google.devtools.build.lib.vfs.FileSystem;
import com.google.devtools.build.lib.vfs.Path;
import java.io.IOException;
import java.util.concurrent.ExecutionException;
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 cached mapping from filename to metadata that may be populated only once.
*/
@ThreadSafe
public class SingleBuildFileCache implements MetadataProvider {
private final Path execRoot;
public SingleBuildFileCache(String cwd, FileSystem fs) {
this.execRoot = fs.getPath(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 Cache<String, ActionInputMetadata> pathToMetadata =
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();
@Override
public FileArtifactValue getMetadata(ActionInput input) throws IOException {
try {
return pathToMetadata
.get(
input.getExecPathString(),
() -> {
Path path =
(input instanceof Artifact)
? ((Artifact) input).getPath()
: execRoot.getRelative(input.getExecPath());
try {
FileArtifactValue metadata = FileArtifactValue.create(path);
if (metadata.getType().isDirectory()) {
throw new DigestOfDirectoryException(
"Input is a directory: " + input.getExecPathString());
}
return new ActionInputMetadata(input, metadata);
} catch (IOException e) {
return new ActionInputMetadata(input, e);
}
})
.getMetadata();
} catch (ExecutionException e) {
throw new IllegalStateException("Unexpected cache loading error", e); // Should never happen.
}
}
@Override
@Nullable
public ActionInput getInput(String execPath) {
ActionInputMetadata metadata = pathToMetadata.getIfPresent(execPath);
if (metadata == null) {
return null;
}
return metadata.getInput();
}
/** Container class for caching I/O around ActionInputs. */
private static class ActionInputMetadata {
private final ActionInput input;
private final FileArtifactValue metadata;
private final IOException exceptionOnAccess;
/** Constructor for a successful lookup. */
ActionInputMetadata(ActionInput input, FileArtifactValue metadata) {
this.input = input;
this.metadata = metadata;
this.exceptionOnAccess = null;
}
/** Constructor for a failed lookup, size will be 0. */
ActionInputMetadata(ActionInput input, IOException exceptionOnAccess) {
this.input = input;
this.exceptionOnAccess = exceptionOnAccess;
this.metadata = null;
}
FileArtifactValue getMetadata() throws IOException {
maybeRaiseException();
return metadata;
}
ActionInput getInput() {
return input;
}
private void maybeRaiseException() throws IOException {
if (exceptionOnAccess != null) {
throw exceptionOnAccess;
}
}
}
}
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