// 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.skyframe;
import static com.google.devtools.build.skyframe.ParallelEvaluator.isDoneForBuild;
import static com.google.devtools.build.skyframe.ParallelEvaluator.maybeMarkRebuilding;
import com.google.common.base.Predicate;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.common.collect.Maps;
import com.google.common.collect.Sets;
import com.google.devtools.build.lib.profiler.AutoProfiler;
import com.google.devtools.build.lib.util.GroupedList;
import com.google.devtools.build.lib.util.Preconditions;
import com.google.devtools.build.skyframe.ParallelEvaluatorContext.EnqueueParentBehavior;
import com.google.devtools.build.skyframe.QueryableGraph.Reason;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Deque;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.logging.Logger;
import javax.annotation.Nullable;
/**
* Depth-first implementation of cycle detection after a {@link ParallelEvaluator} evaluation has
* completed with at least one root unfinished.
*/
class SimpleCycleDetector implements CycleDetector {
private static final Logger logger = Logger.getLogger(SimpleCycleDetector.class.getName());
@Override
public void checkForCycles(
Iterable<SkyKey> badRoots,
EvaluationResult.Builder<?> result,
ParallelEvaluatorContext evaluatorContext)
throws InterruptedException {
try (AutoProfiler p = AutoProfiler.logged("Checking for Skyframe cycles", logger, 10)) {
for (SkyKey root : badRoots) {
ErrorInfo errorInfo = checkForCycles(root, evaluatorContext);
if (errorInfo == null) {
// This node just wasn't finished when evaluation aborted -- there were no cycles below
// it.
Preconditions.checkState(!evaluatorContext.keepGoing(), "", root, badRoots);
continue;
}
Preconditions.checkState(
!Iterables.isEmpty(errorInfo.getCycleInfo()),
"%s was not evaluated, but was not part of a cycle",
root);
result.addError(root, errorInfo);
if (!evaluatorContext.keepGoing()) {
return;
}
}
}
}
/**
* Marker value that we push onto a stack before we push a node's children on. When the marker
* value is popped, we know that all the children are finished. We would use null instead, but
* ArrayDeque does not permit null elements.
*/
private static final SkyKey CHILDREN_FINISHED =
LegacySkyKey.create(SkyFunctionName.create("MARKER"), "MARKER");
/** The max number of cycles we will report to the user for a given root, to avoid OOMing. */
private static final int MAX_CYCLES = 20;
/**
* The algorithm for this cycle detector is as follows. We visit the graph depth-first, keeping
* track of the path we are currently on. We skip any DONE nodes (they are transitively
* error-free). If we come to a node already on the path, we immediately construct a cycle. If we
* are in the noKeepGoing case, we return ErrorInfo with that cycle to the caller. Otherwise, we
* continue. Once all of a node's children are done, we construct an error value for it, based on
* those children. Finally, when the original root's node is constructed, we return its ErrorInfo.
*/
private static ErrorInfo checkForCycles(SkyKey root, ParallelEvaluatorContext evaluatorContext)
throws InterruptedException {
// The number of cycles found. Do not keep on searching for more cycles after this many were
// found.
int cyclesFound = 0;
// The path through the graph currently being visited.
List<SkyKey> graphPath = new ArrayList<>();
// Set of nodes on the path, to avoid expensive searches through the path for cycles.
Set<SkyKey> pathSet = new HashSet<>();
// Maintain a stack explicitly instead of recursion to avoid stack overflows
// on extreme graphs (with long dependency chains).
Deque<SkyKey> toVisit = new ArrayDeque<>();
toVisit.push(root);
// The procedure for this check is as follows: we visit a node, push it onto the graph path,
// push a marker value onto the toVisit stack, and then push all of its children onto the
// toVisit stack. Thus, when the marker node comes to the top of the toVisit stack, we have
// visited the downward transitive closure of the value. At that point, all of its children must
// be finished, and so we can build the definitive error info for the node, popping it off the
// graph path.
while (!toVisit.isEmpty()) {
SkyKey key = toVisit.pop();
NodeEntry entry;
if (key == CHILDREN_FINISHED) {
// We have reached the marker node - that means all children of a node have been visited.
// Since all nodes have errors, we must have found errors in the children at this point.
key = graphPath.remove(graphPath.size() - 1);
entry =
Preconditions.checkNotNull(
evaluatorContext.getGraph().get(null, Reason.CYCLE_CHECKING, key), key);
pathSet.remove(key);
// Skip this node if it was first/last node of a cycle, and so has already been processed.
if (entry.isDone()) {
continue;
}
if (!evaluatorContext.keepGoing()) {
// in the --nokeep_going mode, we would have already returned if we'd found a cycle below
// this node. We haven't, so there are no cycles below this node; skip further evaluation
continue;
}
Set<SkyKey> removedDeps = ImmutableSet.of();
if (cyclesFound < MAX_CYCLES) {
// Value must be ready, because all of its children have finished, so we can build its
// error.
Preconditions.checkState(entry.isReady(), "%s not ready. ValueEntry: %s", key, entry);
} else if (!entry.isReady()) {
removedDeps =
removeIncompleteChildrenForCycle(
key, entry, Iterables.concat(entry.getTemporaryDirectDeps()), evaluatorContext);
}
maybeMarkRebuilding(entry);
GroupedList<SkyKey> directDeps = entry.getTemporaryDirectDeps();
// Find out which children have errors. Similar logic to that in Evaluate#run().
List<ErrorInfo> errorDeps =
getChildrenErrorsForCycle(key, Iterables.concat(directDeps), evaluatorContext);
Preconditions.checkState(
!errorDeps.isEmpty(),
"Node %s was not successfully evaluated, but had no child errors. NodeEntry: %s",
key,
entry);
SkyFunctionEnvironment env =
new SkyFunctionEnvironment(
key,
directDeps,
Sets.difference(entry.getAllRemainingDirtyDirectDeps(), removedDeps),
evaluatorContext);
env.setError(
entry, ErrorInfo.fromChildErrors(key, errorDeps), /*isDirectlyTransient=*/ false);
env.commit(entry, EnqueueParentBehavior.SIGNAL);
} else {
entry = evaluatorContext.getGraph().get(null, Reason.CYCLE_CHECKING, key);
}
Preconditions.checkNotNull(entry, key);
// Nothing to be done for this node if it already has an entry.
if (entry.isDone()) {
continue;
}
if (cyclesFound == MAX_CYCLES) {
// Do not keep on searching for cycles indefinitely, to avoid excessive runtime/OOMs.
continue;
}
if (pathSet.contains(key)) {
int cycleStart = graphPath.indexOf(key);
// Found a cycle!
cyclesFound++;
Iterable<SkyKey> cycle = graphPath.subList(cycleStart, graphPath.size());
logger.info("Found cycle : " + cycle + " from " + graphPath);
// Put this node into a consistent state for building if it is dirty.
if (entry.isDirty() && entry.getDirtyState() == NodeEntry.DirtyState.CHECK_DEPENDENCIES) {
// In the check deps state, entry has exactly one child not done yet. Note that this node
// must be part of the path to the cycle we have found (since done nodes cannot be in
// cycles, and this is the only missing one). Thus, it will not be removed below in
// removeDescendantsOfCycleValue, so it is safe here to signal that it is done.
entry.signalDep();
maybeMarkRebuilding(entry);
}
if (evaluatorContext.keepGoing()) {
// Any children of this node that we haven't already visited are not worth visiting,
// since this node is about to be done. Thus, the only child worth visiting is the one in
// this cycle, the cycleChild (which may == key if this cycle is a self-edge).
SkyKey cycleChild = selectCycleChild(key, graphPath, cycleStart);
Set<SkyKey> removedDeps =
removeDescendantsOfCycleValue(
key, entry, cycleChild, toVisit, graphPath.size() - cycleStart, evaluatorContext);
ValueWithMetadata dummyValue = ValueWithMetadata.wrapWithMetadata(new SkyValue() {});
SkyFunctionEnvironment env =
new SkyFunctionEnvironment(
key,
entry.getTemporaryDirectDeps(),
ImmutableMap.of(cycleChild, dummyValue),
Sets.difference(entry.getAllRemainingDirtyDirectDeps(), removedDeps),
evaluatorContext);
// Construct error info for this node. Get errors from children, which are all done
// except possibly for the cycleChild.
List<ErrorInfo> allErrors =
getChildrenErrorsForCycleChecking(
Iterables.concat(entry.getTemporaryDirectDeps()),
/*unfinishedChild=*/ cycleChild,
evaluatorContext);
CycleInfo cycleInfo = new CycleInfo(cycle);
// Add in this cycle.
allErrors.add(ErrorInfo.fromCycle(cycleInfo));
env.setError(entry, ErrorInfo.fromChildErrors(key, allErrors), /*isTransient=*/ false);
env.commit(entry, EnqueueParentBehavior.SIGNAL);
continue;
} else {
// We need to return right away in the noKeepGoing case, so construct the cycle (with the
// path) and return.
Preconditions.checkState(
graphPath.get(0).equals(root),
"%s not reached from %s. ValueEntry: %s",
key,
root,
entry);
return ErrorInfo.fromCycle(new CycleInfo(graphPath.subList(0, cycleStart), cycle));
}
}
// This node is not yet known to be in a cycle. So process its children.
Iterable<SkyKey> children = Iterables.concat(entry.getTemporaryDirectDeps());
if (Iterables.isEmpty(children)) {
continue;
}
// Prefetch all children, in case our graph performs better with a primed cache. No need to
// recurse into done nodes. The fields of done nodes aren't necessary, since we'll filter them
// out.
// TODO(janakr): If graph implementations start using these hints for not-done nodes, we may
// have to change this.
Map<SkyKey, ? extends NodeEntry> childrenNodes =
evaluatorContext.getGraph().getBatch(key, Reason.EXISTENCE_CHECKING, children);
Preconditions.checkState(childrenNodes.size() == Iterables.size(children), childrenNodes);
children =
Maps.filterValues(
childrenNodes,
new Predicate<NodeEntry>() {
@Override
public boolean apply(NodeEntry nodeEntry) {
return !nodeEntry.isDone();
}
})
.keySet();
// This marker flag will tell us when all this node's children have been processed.
toVisit.push(CHILDREN_FINISHED);
// This node is now part of the path through the graph.
graphPath.add(key);
pathSet.add(key);
for (SkyKey nextValue : children) {
toVisit.push(nextValue);
}
}
return evaluatorContext.keepGoing()
? getAndCheckDoneForCycle(root, evaluatorContext).getErrorInfo()
: null;
}
/**
* Returns the child of this node that is in the cycle that was just found. If the cycle is a
* self-edge, returns the node itself.
*/
private static SkyKey selectCycleChild(SkyKey key, List<SkyKey> graphPath, int cycleStart) {
return cycleStart + 1 == graphPath.size() ? key : graphPath.get(cycleStart + 1);
}
/**
* Get all the errors of child nodes. There must be at least one cycle amongst them.
*
* @param children child nodes to query for errors.
* @return List of ErrorInfos from all children that had errors.
*/
private static List<ErrorInfo> getChildrenErrorsForCycle(
SkyKey parent, Iterable<SkyKey> children, ParallelEvaluatorContext evaluatorContext)
throws InterruptedException {
List<ErrorInfo> allErrors = new ArrayList<>();
boolean foundCycle = false;
for (NodeEntry childNode :
getAndCheckDoneBatchForCycle(parent, children, evaluatorContext).values()) {
ErrorInfo errorInfo = childNode.getErrorInfo();
if (errorInfo != null) {
foundCycle |= !Iterables.isEmpty(errorInfo.getCycleInfo());
allErrors.add(errorInfo);
}
}
Preconditions.checkState(foundCycle, "", children, allErrors);
return allErrors;
}
/**
* Get all the errors of child nodes.
*
* @param children child nodes to query for errors.
* @param unfinishedChild child which is allowed to not be done.
* @return List of ErrorInfos from all children that had errors.
*/
private static List<ErrorInfo> getChildrenErrorsForCycleChecking(
Iterable<SkyKey> children, SkyKey unfinishedChild, ParallelEvaluatorContext evaluatorContext)
throws InterruptedException {
List<ErrorInfo> allErrors = new ArrayList<>();
Set<? extends Map.Entry<SkyKey, ? extends NodeEntry>> childEntries =
evaluatorContext.getBatchValues(null, Reason.CYCLE_CHECKING, children).entrySet();
for (Map.Entry<SkyKey, ? extends NodeEntry> childMapEntry : childEntries) {
SkyKey childKey = childMapEntry.getKey();
NodeEntry childNodeEntry = childMapEntry.getValue();
ErrorInfo errorInfo =
getErrorMaybe(
childKey, childNodeEntry, /*allowUnfinished=*/ childKey.equals(unfinishedChild));
if (errorInfo != null) {
allErrors.add(errorInfo);
}
}
return allErrors;
}
@Nullable
private static ErrorInfo getErrorMaybe(
SkyKey key, NodeEntry childNodeEntry, boolean allowUnfinished) throws InterruptedException {
Preconditions.checkNotNull(childNodeEntry, key);
if (!allowUnfinished) {
return checkDone(key, childNodeEntry).getErrorInfo();
}
return childNodeEntry.isDone() ? childNodeEntry.getErrorInfo() : null;
}
/**
* Removes direct children of key from toVisit and from the entry itself, and makes the entry
* ready if necessary. We must do this because it would not make sense to try to build the
* children after building the entry. It would violate the invariant that a parent can only be
* built after its children are built; See bug "Precondition error while evaluating a Skyframe
* graph with a cycle".
*
* @param key SkyKey of node in a cycle.
* @param entry NodeEntry of node in a cycle.
* @param cycleChild direct child of key in the cycle, or key itself if the cycle is a self-edge.
* @param toVisit list of remaining nodes to visit by the cycle-checker.
* @param cycleLength the length of the cycle found.
*/
private static Set<SkyKey> removeDescendantsOfCycleValue(
SkyKey key,
NodeEntry entry,
@Nullable SkyKey cycleChild,
Iterable<SkyKey> toVisit,
int cycleLength,
ParallelEvaluatorContext evaluatorContext)
throws InterruptedException {
GroupedList<SkyKey> directDeps = entry.getTemporaryDirectDeps();
Set<SkyKey> unvisitedDeps = Sets.newHashSetWithExpectedSize(directDeps.numElements());
Iterables.addAll(unvisitedDeps, Iterables.concat(directDeps));
unvisitedDeps.remove(cycleChild);
// Remove any children from this node that are not part of the cycle we just found. They are
// irrelevant to the node as it stands, and if they are deleted from the graph because they are
// not built by the end of cycle-checking, we would have dangling references.
Set<SkyKey> removedDeps =
removeIncompleteChildrenForCycle(key, entry, unvisitedDeps, evaluatorContext);
if (!entry.isReady()) {
// The entry has at most one undone dep now, its cycleChild. Signal to make entry ready. Note
// that the entry can conceivably be ready if its cycleChild already found a different cycle
// and was built.
entry.signalDep();
}
maybeMarkRebuilding(entry);
Preconditions.checkState(entry.isReady(), "%s %s %s", key, cycleChild, entry);
Iterator<SkyKey> it = toVisit.iterator();
while (it.hasNext()) {
SkyKey descendant = it.next();
if (descendant == CHILDREN_FINISHED) {
// Marker value, delineating the end of a group of children that were enqueued.
cycleLength--;
if (cycleLength == 0) {
// We have seen #cycleLength-1 marker values, and have arrived at the one for this value,
// so we are done.
return removedDeps;
}
continue; // Don't remove marker values.
}
if (cycleLength == 1) {
// Remove the direct children remaining to visit of the cycle node.
Preconditions.checkState(
unvisitedDeps.contains(descendant),
"%s %s %s %s %s",
key,
descendant,
cycleChild,
unvisitedDeps,
entry);
it.remove();
}
}
throw new IllegalStateException(
String.format(
"There were not %d groups of children in %s when trying to remove children of %s other "
+ "than %s",
cycleLength, toVisit, key, cycleChild));
}
private static Set<SkyKey> removeIncompleteChildrenForCycle(
SkyKey key,
NodeEntry entry,
Iterable<SkyKey> children,
ParallelEvaluatorContext evaluatorContext)
throws InterruptedException {
Set<SkyKey> unfinishedDeps = new HashSet<>();
for (SkyKey child : children) {
if (removeIncompleteChildForCycle(key, child, evaluatorContext)) {
unfinishedDeps.add(child);
}
}
entry.removeUnfinishedDeps(unfinishedDeps);
return unfinishedDeps;
}
private static NodeEntry checkDone(SkyKey key, NodeEntry entry) {
Preconditions.checkNotNull(entry, key);
Preconditions.checkState(entry.isDone(), "%s %s", key, entry);
return entry;
}
private static NodeEntry getAndCheckDoneForCycle(
SkyKey key, ParallelEvaluatorContext evaluatorContext) throws InterruptedException {
return checkDone(key, evaluatorContext.getGraph().get(null, Reason.CYCLE_CHECKING, key));
}
private static Map<SkyKey, ? extends NodeEntry> getAndCheckDoneBatchForCycle(
SkyKey parent, Iterable<SkyKey> keys, ParallelEvaluatorContext evaluatorContext)
throws InterruptedException {
Map<SkyKey, ? extends NodeEntry> nodes =
evaluatorContext.getBatchValues(parent, Reason.CYCLE_CHECKING, keys);
for (Map.Entry<SkyKey, ? extends NodeEntry> nodeEntryMapEntry : nodes.entrySet()) {
checkDone(nodeEntryMapEntry.getKey(), nodeEntryMapEntry.getValue());
}
return nodes;
}
/**
* If child is not done, removes {@param inProgressParent} from {@param child}'s reverse deps.
* Returns whether child should be removed from inProgressParent's entry's direct deps.
*/
private static boolean removeIncompleteChildForCycle(
SkyKey inProgressParent, SkyKey child, ParallelEvaluatorContext evaluatorContext)
throws InterruptedException {
NodeEntry childEntry =
evaluatorContext.getGraph().get(inProgressParent, Reason.CYCLE_CHECKING, child);
if (!isDoneForBuild(childEntry)) {
childEntry.removeInProgressReverseDep(inProgressParent);
return true;
}
return false;
}
}