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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.skyframe;
import com.google.common.base.Preconditions;
import com.google.common.base.Predicate;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.common.collect.Sets;
import com.google.devtools.build.lib.actions.FileStateType;
import com.google.devtools.build.lib.actions.FileStateValue;
import com.google.devtools.build.lib.actions.FileValue;
import com.google.devtools.build.lib.pkgcache.PathPackageLocator;
import com.google.devtools.build.lib.util.Pair;
import com.google.devtools.build.lib.vfs.Path;
import com.google.devtools.build.lib.vfs.PathFragment;
import com.google.devtools.build.lib.vfs.RootedPath;
import com.google.devtools.build.skyframe.SkyFunction;
import com.google.devtools.build.skyframe.SkyFunctionException;
import com.google.devtools.build.skyframe.SkyFunctionException.Transience;
import com.google.devtools.build.skyframe.SkyKey;
import java.io.IOException;
import java.util.ArrayList;
import java.util.TreeSet;
import java.util.concurrent.atomic.AtomicReference;
import javax.annotation.Nullable;
/**
* A {@link SkyFunction} for {@link FileValue}s.
*
* <p>Most of the complexity in the implementation results from wanting incremental correctness in
* the presence of symlinks, esp. ancestor directory symlinks.
*/
public class FileFunction implements SkyFunction {
private final AtomicReference<PathPackageLocator> pkgLocator;
@Nullable private final NonexistentFileReceiver nonexistentFileReceiver;
/** Temporary interface to help track down why files are missing in some cases. */
public interface NonexistentFileReceiver {
void accept(
RootedPath rootedPath,
RootedPath realRootedPath,
RootedPath parentRootedPath,
FileValue parentFileValue);
}
public FileFunction(AtomicReference<PathPackageLocator> pkgLocator) {
this(pkgLocator, null);
}
FileFunction(
AtomicReference<PathPackageLocator> pkgLocator,
@Nullable NonexistentFileReceiver nonexistentFileReceiver) {
this.pkgLocator = pkgLocator;
this.nonexistentFileReceiver = nonexistentFileReceiver;
}
@Override
public FileValue compute(SkyKey skyKey, Environment env)
throws FileFunctionException, InterruptedException {
RootedPath rootedPath = (RootedPath) skyKey.argument();
// Suppose we have a path p. One of the goals of FileFunction is to resolve the "real path", if
// any, of p. The basic algorithm is to use the fully resolved path of p's parent directory to
// determine the fully resolved path of p. This is complicated when symlinks are involved, and
// is especially complicated when ancestor directory symlinks are involved.
//
// Since FileStateValues are the roots of invalidation, care has to be taken to ensuring we
// declare the proper FileStateValue deps. As a concrete example, let p = a/b and imagine (i) a
// is a direct symlink to c and also (ii) c/b is an existing file. Among other direct deps, we
// want to have a direct dep on FileStateValue(c/b), since that's the node that will be changed
// if the actual contents of a/b (aka c/b) changes. To rephrase: a dep on FileStateValue(a/b)
// won't do anything productive since that path will never be in the Skyframe diff.
//
// In the course of resolving the real path of p, there will be a logical chain of paths we
// consider. Going with the example from above, the full chain of paths we consider is
// [a/b, c/b].
ArrayList<RootedPath> logicalChain = new ArrayList<>();
// Same contents as 'logicalChain', except stored as an sorted TreeSet for efficiency reasons.
// See the usage in checkPathSeenDuringPartialResolutionInternal.
TreeSet<Path> sortedLogicalChain = Sets.newTreeSet();
// Fully resolve the path of the parent directory, but only if the current file is not the
// filesystem root (has no parent) or a package path root (treated opaquely and handled by
// skyframe's DiffAwareness interface).
//
// This entails resolving ancestor symlinks fully. Note that this is the first thing we do - if
// an ancestor is part of a symlink cycle, we want to detect that quickly as it gives a more
// informative error message than we'd get doing bogus filesystem operations.
PartialResolutionResult resolveFromAncestorsResult =
resolveFromAncestors(rootedPath, sortedLogicalChain, logicalChain, env);
if (resolveFromAncestorsResult == null) {
return null;
}
RootedPath rootedPathFromAncestors = resolveFromAncestorsResult.rootedPath;
FileStateValue fileStateValueFromAncestors = resolveFromAncestorsResult.fileStateValue;
if (fileStateValueFromAncestors.getType() == FileStateType.NONEXISTENT) {
return FileValue.value(
ImmutableList.copyOf(logicalChain),
rootedPath,
FileStateValue.NONEXISTENT_FILE_STATE_NODE,
rootedPathFromAncestors,
fileStateValueFromAncestors);
}
RootedPath realRootedPath = rootedPathFromAncestors;
FileStateValue realFileStateValue = fileStateValueFromAncestors;
while (realFileStateValue.getType().isSymlink()) {
PartialResolutionResult getSymlinkTargetRootedPathResult =
getSymlinkTargetRootedPath(
realRootedPath,
realFileStateValue.getSymlinkTarget(),
sortedLogicalChain,
logicalChain,
env);
if (getSymlinkTargetRootedPathResult == null) {
return null;
}
realRootedPath = getSymlinkTargetRootedPathResult.rootedPath;
realFileStateValue = getSymlinkTargetRootedPathResult.fileStateValue;
}
return FileValue.value(
ImmutableList.copyOf(logicalChain),
rootedPath,
// TODO(b/123922036): This is a bug. Should be 'fileStateValueFromAncestors'.
fileStateValueFromAncestors,
realRootedPath,
realFileStateValue);
}
private static RootedPath getChild(RootedPath parentRootedPath, String baseName) {
return RootedPath.toRootedPath(
parentRootedPath.getRoot(), parentRootedPath.getRootRelativePath().getChild(baseName));
}
private RootedPath toRootedPath(Path path) {
return RootedPath.toRootedPathMaybeUnderRoot(path, pkgLocator.get().getPathEntries());
}
/**
* Returns the path and file state of {@code rootedPath}, accounting for ancestor symlinks, or
* {@code null} if there was a missing dep.
*/
@Nullable
private PartialResolutionResult resolveFromAncestors(
RootedPath rootedPath,
TreeSet<Path> sortedLogicalChain,
ArrayList<RootedPath> logicalChain,
Environment env)
throws InterruptedException, FileFunctionException {
RootedPath parentRootedPath = rootedPath.getParentDirectory();
return parentRootedPath != null
? resolveFromAncestorsWithParent(
rootedPath, parentRootedPath, sortedLogicalChain, logicalChain, env)
: resolveFromAncestorsNoParent(rootedPath, sortedLogicalChain, logicalChain, env);
}
@Nullable
private PartialResolutionResult resolveFromAncestorsWithParent(
RootedPath rootedPath,
RootedPath parentRootedPath,
TreeSet<Path> sortedLogicalChain,
ArrayList<RootedPath> logicalChain,
Environment env)
throws InterruptedException, FileFunctionException {
PathFragment relativePath = rootedPath.getRootRelativePath();
RootedPath rootedPathFromAncestors;
String baseName = relativePath.getBaseName();
FileValue parentFileValue = (FileValue) env.getValue(FileValue.key(parentRootedPath));
if (parentFileValue == null) {
return null;
}
rootedPathFromAncestors = getChild(parentFileValue.realRootedPath(), baseName);
if (!parentFileValue.exists() || !parentFileValue.isDirectory()) {
if (nonexistentFileReceiver != null) {
nonexistentFileReceiver.accept(
rootedPath, rootedPathFromAncestors, parentRootedPath, parentFileValue);
}
return new PartialResolutionResult(
rootedPathFromAncestors, FileStateValue.NONEXISTENT_FILE_STATE_NODE);
}
for (RootedPath parentPartialRootedPath : parentFileValue.logicalChainDuringResolution()) {
checkAndNotePathSeenDuringPartialResolution(
getChild(parentPartialRootedPath, baseName), sortedLogicalChain, logicalChain, env);
if (env.valuesMissing()) {
return null;
}
}
FileStateValue fileStateValueFromAncestors =
(FileStateValue) env.getValue(FileStateValue.key(rootedPathFromAncestors));
if (fileStateValueFromAncestors == null) {
return null;
}
return new PartialResolutionResult(rootedPathFromAncestors, fileStateValueFromAncestors);
}
@Nullable
private PartialResolutionResult resolveFromAncestorsNoParent(
RootedPath rootedPath,
TreeSet<Path> sortedLogicalChain,
ArrayList<RootedPath> logicalChain,
Environment env)
throws InterruptedException, FileFunctionException {
checkAndNotePathSeenDuringPartialResolution(rootedPath, sortedLogicalChain, logicalChain, env);
if (env.valuesMissing()) {
return null;
}
FileStateValue realFileStateValue =
(FileStateValue) env.getValue(FileStateValue.key(rootedPath));
if (realFileStateValue == null) {
return null;
}
return new PartialResolutionResult(rootedPath, realFileStateValue);
}
private static final class PartialResolutionResult {
private final RootedPath rootedPath;
private final FileStateValue fileStateValue;
private PartialResolutionResult(RootedPath rootedPath, FileStateValue fileStateValue) {
this.rootedPath = rootedPath;
this.fileStateValue = fileStateValue;
}
}
/**
* Returns the symlink target and file state of {@code rootedPath}'s symlink to {@code
* symlinkTarget}, accounting for ancestor symlinks, or {@code null} if there was a missing dep.
*/
@Nullable
private PartialResolutionResult getSymlinkTargetRootedPath(
RootedPath rootedPath,
PathFragment symlinkTarget,
TreeSet<Path> sortedLogicalChain,
ArrayList<RootedPath> logicalChain,
Environment env)
throws FileFunctionException, InterruptedException {
Path path = rootedPath.asPath();
Path symlinkTargetPath;
if (symlinkTarget.isAbsolute()) {
symlinkTargetPath = path.getRelative(symlinkTarget);
} else {
Path parentPath = path.getParentDirectory();
symlinkTargetPath =
parentPath != null
? parentPath.getRelative(symlinkTarget)
: path.getRelative(symlinkTarget);
}
RootedPath symlinkTargetRootedPath = toRootedPath(symlinkTargetPath);
checkPathSeenDuringPartialResolution(
symlinkTargetRootedPath, sortedLogicalChain, logicalChain, env);
if (env.valuesMissing()) {
return null;
}
// The symlink target could have a different parent directory, which itself could be a directory
// symlink (or have an ancestor directory symlink)!
return resolveFromAncestors(symlinkTargetRootedPath, sortedLogicalChain, logicalChain, env);
}
private void checkAndNotePathSeenDuringPartialResolution(
RootedPath rootedPath,
TreeSet<Path> sortedLogicalChain,
ArrayList<RootedPath> logicalChain,
Environment env)
throws FileFunctionException, InterruptedException {
Path path = rootedPath.asPath();
checkPathSeenDuringPartialResolutionInternal(
rootedPath, path, sortedLogicalChain, logicalChain, env);
sortedLogicalChain.add(path);
logicalChain.add(rootedPath);
}
private void checkPathSeenDuringPartialResolution(
RootedPath rootedPath,
TreeSet<Path> sortedLogicalChain,
ArrayList<RootedPath> logicalChain,
Environment env)
throws FileFunctionException, InterruptedException {
checkPathSeenDuringPartialResolutionInternal(
rootedPath, rootedPath.asPath(), sortedLogicalChain, logicalChain, env);
}
private void checkPathSeenDuringPartialResolutionInternal(
RootedPath rootedPath,
Path path,
TreeSet<Path> sortedLogicalChain,
ArrayList<RootedPath> logicalChain,
Environment env)
throws FileFunctionException, InterruptedException {
// We are about to perform another step of partial real path resolution. 'logicalChain' is the
// chain of paths we've considered so far, and 'rootedPath' / 'path' is the proposed next path
// we consider.
//
// Before we proceed with 'rootedPath', we need to ensure there won't be a problem. There are
// three sorts of issues, all stemming from symlinks:
// (i) Symlink cycle:
// p -> p1 -> p2 -> p1
// (ii) Unbounded expansion caused by a symlink to a descendant of a member of the chain:
// p -> a/b -> c/d -> a/b/e
// (iii) Unbounded expansion caused by a symlink to an ancestor of a member of the chain:
// p -> a/b -> c/d -> a
//
// We can detect all three of these symlink issues via inspection of the proposed new element.
// Here is our incremental algorithm:
// If 'path' is in 'sortedLogicalChain' then we have a found a cycle (i).
// If 'path' is a descendant of any path p in 'sortedLogicalChain' then we have unbounded
// expansion (ii).
// If 'path' is an ancestor of any path p in 'sortedLogicalChain' then we have unbounded
// expansion (iii).
// We can check for these cases efficiently (read: sublinear time) by finding the extremal
// candidate p for (ii) and (iii).
SkyKey uniquenessKey = null;
FileSymlinkException fse = null;
Path seenFloorPath = sortedLogicalChain.floor(path);
Path seenCeilingPath = sortedLogicalChain.ceiling(path);
if (sortedLogicalChain.contains(path)) {
// 'rootedPath' is [transitively] a symlink to a previous element in the symlink chain (i).
Pair<ImmutableList<RootedPath>, ImmutableList<RootedPath>> pathAndChain =
CycleUtils.splitIntoPathAndChain(isPathPredicate(path), logicalChain);
FileSymlinkCycleException fsce =
new FileSymlinkCycleException(pathAndChain.getFirst(), pathAndChain.getSecond());
uniquenessKey = FileSymlinkCycleUniquenessFunction.key(fsce.getCycle());
fse = fsce;
} else if (seenFloorPath != null && path.startsWith(seenFloorPath)) {
// 'rootedPath' is [transitively] a symlink to a descendant of a previous element in the
// symlink chain (ii).
Pair<ImmutableList<RootedPath>, ImmutableList<RootedPath>> pathAndChain =
CycleUtils.splitIntoPathAndChain(
isPathPredicate(seenFloorPath),
ImmutableList.copyOf(Iterables.concat(logicalChain, ImmutableList.of(rootedPath))));
uniquenessKey = FileSymlinkInfiniteExpansionUniquenessFunction.key(pathAndChain.getSecond());
fse = new FileSymlinkInfiniteExpansionException(
pathAndChain.getFirst(), pathAndChain.getSecond());
} else if (seenCeilingPath != null && seenCeilingPath.startsWith(path)) {
// 'rootedPath' is [transitively] a symlink to an ancestor of a previous element in the
// symlink chain (iii).
Pair<ImmutableList<RootedPath>, ImmutableList<RootedPath>> pathAndChain =
CycleUtils.splitIntoPathAndChain(
isPathPredicate(seenCeilingPath),
ImmutableList.copyOf(Iterables.concat(logicalChain, ImmutableList.of(rootedPath))));
uniquenessKey = FileSymlinkInfiniteExpansionUniquenessFunction.key(pathAndChain.getSecond());
fse =
new FileSymlinkInfiniteExpansionException(
pathAndChain.getFirst(), pathAndChain.getSecond());
}
if (uniquenessKey != null) {
// Note that this dependency is merely to ensure that each unique symlink error gets
// reported exactly once.
env.getValue(uniquenessKey);
if (env.valuesMissing()) {
return;
}
throw new FileFunctionException(
Preconditions.checkNotNull(fse, rootedPath), Transience.PERSISTENT);
}
}
private static final Predicate<RootedPath> isPathPredicate(final Path path) {
return new Predicate<RootedPath>() {
@Override
public boolean apply(RootedPath rootedPath) {
return rootedPath.asPath().equals(path);
}
};
}
@Nullable
@Override
public String extractTag(SkyKey skyKey) {
return null;
}
/**
* Used to declare all the exception types that can be wrapped in the exception thrown by
* {@link FileFunction#compute}.
*/
private static final class FileFunctionException extends SkyFunctionException {
public FileFunctionException(IOException e, Transience transience) {
super(e, transience);
}
}
}