blob: 08e15127cc41bdead5e375085d9b1c7232f9b506 [file] [log] [blame]
// 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.actions;
import com.google.devtools.build.lib.util.Fingerprint;
import com.google.devtools.build.lib.vfs.FileStatus;
import java.io.IOException;
import java.util.Objects;
/**
* In case we can't get a fast digest from the filesystem, we store this metadata as a proxy to the
* file contents. Currently it is two timestamps and a "node id". On Linux we use both ctime and
* mtime and inode number. We might want to add the device number in the future.
*
* <p>For a Linux example of why mtime alone is insufficient, note that 'mv' preserves mtime. So if
* files 'a' and 'b' initially have the same timestamp, then we would think 'b' is unchanged after
* the user executes `mv a b` between two builds.
*
* <p>On Linux we also need mtime for hardlinking sandbox, since updating the inode reference
* counter preserves mtime, but updates ctime. isModified() call can be used to compare two
* FileContentsProxys of hardlinked files.
*/
public final class FileContentsProxy {
private final long ctime;
private final long mtime;
private final long nodeId;
public FileContentsProxy(long ctime, long mtime, long nodeId) {
this.ctime = ctime;
this.mtime = mtime;
this.nodeId = nodeId;
}
public static FileContentsProxy create(FileStatus stat) throws IOException {
// Note: there are file systems that return mtime for this call instead of ctime, such as the
// WindowsFileSystem.
return new FileContentsProxy(
stat.getLastChangeTime(), stat.getLastModifiedTime(), stat.getNodeId());
}
@Override
public boolean equals(Object other) {
if (other == this) {
return true;
}
if (!(other instanceof FileContentsProxy)) {
return false;
}
FileContentsProxy that = (FileContentsProxy) other;
return ctime == that.ctime && mtime == that.mtime && nodeId == that.nodeId;
}
/**
* Can be used when hardlink reference counter changes should not be considered a file
* modification. Is only comparing mtime and not ctime and is therefore not detecting changed
* metadata like permission.
*/
@SuppressWarnings("ReferenceEquality")
public boolean isModified(FileContentsProxy other) {
if (other == this) {
return false;
}
// true if nodeId are different or inode has a new mtime
return nodeId != other.nodeId || mtime != other.mtime;
}
@Override
public int hashCode() {
return Objects.hash(ctime, mtime, nodeId);
}
void addToFingerprint(Fingerprint fp) {
fp.addLong(ctime);
fp.addLong(mtime);
fp.addLong(nodeId);
}
@Override
public String toString() {
return prettyPrint();
}
public String prettyPrint() {
return String.format("ctime of %d and mtime of %d and nodeId of %d", ctime, mtime, nodeId);
}
}