// 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.skyframe;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Function;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableList.Builder;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.common.collect.Sets;
import com.google.devtools.build.lib.concurrent.AbstractQueueVisitor;
import com.google.devtools.build.lib.concurrent.ErrorClassifier;
import com.google.devtools.build.lib.concurrent.ExecutorParams;
import com.google.devtools.build.lib.concurrent.ForkJoinQuiescingExecutor;
import com.google.devtools.build.lib.concurrent.QuiescingExecutor;
import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
import com.google.devtools.build.lib.util.Pair;
import com.google.devtools.build.lib.util.Preconditions;
import com.google.devtools.build.skyframe.QueryableGraph.Reason;
import com.google.devtools.build.skyframe.ThinNodeEntry.MarkedDirtyResult;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.TimeUnit;
import javax.annotation.Nullable;
/**
* A visitor that is useful for invalidating transitive dependencies of Skyframe nodes.
*
* <p>Interruptibility: It is safe to interrupt the invalidation process at any time. Consider a
* graph and a set of modified nodes. Then the reverse transitive closure of the modified nodes is
* the set of dirty nodes. We provide interruptibility by making sure that the following invariant
* holds at any time:
*
* <p>If a node is dirty, but not removed (or marked as dirty) yet, then either it or any of its
* transitive dependencies must be in the {@link #pendingVisitations} set. Furthermore, reverse dep
* pointers must always point to existing nodes.
*
* <p>Thread-safety: This class should only be instantiated and called on a single thread, but
* internally it spawns many worker threads to process the graph. The thread-safety of the workers
* on the graph can be delicate, and is documented below. Moreover, no other modifications to the
* graph can take place while invalidation occurs.
*
* <p>This is intended only for use in alternative {@code MemoizingEvaluator} implementations.
*/
public abstract class InvalidatingNodeVisitor<TGraph extends QueryableGraph> {
// Default thread count is equal to the number of cores to exploit
// that level of hardware parallelism, since invalidation should be CPU-bound.
// We may consider increasing this in the future.
private static final int DEFAULT_THREAD_COUNT = Runtime.getRuntime().availableProcessors();
private static final int EXPECTED_PENDING_SET_SIZE = DEFAULT_THREAD_COUNT * 8;
private static final int EXPECTED_VISITED_SET_SIZE = 1024;
private static final ErrorClassifier errorClassifier =
new ErrorClassifier() {
@Override
protected ErrorClassification classifyException(Exception e) {
return e instanceof RuntimeException
? ErrorClassification.CRITICAL_AND_LOG
: ErrorClassification.NOT_CRITICAL;
}
};
protected final TGraph graph;
protected final DirtyTrackingProgressReceiver progressReceiver;
// Aliased to InvalidationState.pendingVisitations.
protected final Set<Pair<SkyKey, InvalidationType>> pendingVisitations;
protected final QuiescingExecutor executor;
protected InvalidatingNodeVisitor(
TGraph graph,
DirtyTrackingProgressReceiver progressReceiver,
InvalidationState state) {
this(
graph, progressReceiver, state, AbstractQueueVisitor.EXECUTOR_FACTORY);
}
protected InvalidatingNodeVisitor(
TGraph graph,
DirtyTrackingProgressReceiver progressReceiver,
InvalidationState state,
Function<ExecutorParams, ? extends ExecutorService> executorFactory) {
this.executor =
new AbstractQueueVisitor(
/*parallelism=*/ DEFAULT_THREAD_COUNT,
/*keepAliveTime=*/ 1,
/*units=*/ TimeUnit.SECONDS,
/*failFastOnException=*/ true,
"skyframe-invalidator",
executorFactory,
errorClassifier);
this.graph = Preconditions.checkNotNull(graph);
this.progressReceiver = Preconditions.checkNotNull(progressReceiver);
this.pendingVisitations = state.pendingValues;
}
protected InvalidatingNodeVisitor(
TGraph graph,
DirtyTrackingProgressReceiver progressReceiver,
InvalidationState state,
ForkJoinPool forkJoinPool) {
this.executor = ForkJoinQuiescingExecutor.newBuilder()
.withOwnershipOf(forkJoinPool)
.setErrorClassifier(errorClassifier)
.build();
this.graph = Preconditions.checkNotNull(graph);
this.progressReceiver = Preconditions.checkNotNull(progressReceiver);
this.pendingVisitations = state.pendingValues;
}
/** Initiates visitation and waits for completion. */
void run() throws InterruptedException {
// Make a copy to avoid concurrent modification confusing us as to which nodes were passed by
// the caller, and which are added by other threads during the run. Since no tasks have been
// started yet (the queueDirtying calls start them), this is thread-safe.
for (final Pair<SkyKey, InvalidationType> visitData :
ImmutableList.copyOf(pendingVisitations)) {
executor.execute(
new Runnable() {
@Override
public void run() {
visit(ImmutableList.of(visitData.first), visitData.second);
}
});
}
executor.awaitQuiescence(/*interruptWorkers=*/ true);
// Note: implementations that do not support interruption also do not update pendingVisitations.
Preconditions.checkState(!getSupportInterruptions() || pendingVisitations.isEmpty(),
"All dirty nodes should have been processed: %s", pendingVisitations);
}
protected abstract boolean getSupportInterruptions();
@VisibleForTesting
CountDownLatch getInterruptionLatchForTestingOnly() {
return executor.getInterruptionLatchForTestingOnly();
}
/** Enqueues nodes for invalidation. Elements of {@code keys} may not exist in the graph. */
@ThreadSafe
abstract void visit(Iterable<SkyKey> keys, InvalidationType invalidationType);
@VisibleForTesting
enum InvalidationType {
/** The node is dirty and must be recomputed. */
CHANGED,
/** The node is dirty, but may be marked clean later during change pruning. */
DIRTIED,
/** The node is deleted. */
DELETED;
}
/**
* Invalidation state object that keeps track of which nodes need to be invalidated, but have not
* been dirtied/deleted yet. This supports interrupts - by only deleting a node from this set
* when all its parents have been invalidated, we ensure that no information is lost when an
* interrupt comes in.
*/
static class InvalidationState {
private final Set<Pair<SkyKey, InvalidationType>> pendingValues =
Collections.newSetFromMap(
new ConcurrentHashMap<Pair<SkyKey, InvalidationType>, Boolean>(
EXPECTED_PENDING_SET_SIZE, .75f, DEFAULT_THREAD_COUNT));
private final InvalidationType defaultUpdateType;
private InvalidationState(InvalidationType defaultUpdateType) {
this.defaultUpdateType = Preconditions.checkNotNull(defaultUpdateType);
}
void update(Iterable<SkyKey> diff) {
Iterables.addAll(pendingValues, Iterables.transform(diff,
new Function<SkyKey, Pair<SkyKey, InvalidationType>>() {
@Override
public Pair<SkyKey, InvalidationType> apply(SkyKey skyKey) {
return Pair.of(skyKey, defaultUpdateType);
}
}));
}
@VisibleForTesting
boolean isEmpty() {
return pendingValues.isEmpty();
}
@VisibleForTesting
Set<Pair<SkyKey, InvalidationType>> getInvalidationsForTesting() {
return ImmutableSet.copyOf(pendingValues);
}
}
public static class DirtyingInvalidationState extends InvalidationState {
public DirtyingInvalidationState() {
super(InvalidationType.CHANGED);
}
}
static class DeletingInvalidationState extends InvalidationState {
DeletingInvalidationState() {
super(InvalidationType.DELETED);
}
}
/** A node-deleting implementation. */
static class DeletingNodeVisitor extends InvalidatingNodeVisitor<InMemoryGraph> {
private final Set<SkyKey> visited = Sets.newConcurrentHashSet();
private final boolean traverseGraph;
DeletingNodeVisitor(
InMemoryGraph graph,
DirtyTrackingProgressReceiver progressReceiver,
InvalidationState state,
boolean traverseGraph) {
super(graph, progressReceiver, state);
this.traverseGraph = traverseGraph;
}
@Override
protected boolean getSupportInterruptions() {
return true;
}
@Override
public void visit(Iterable<SkyKey> keys, InvalidationType invalidationType) {
Preconditions.checkState(invalidationType == InvalidationType.DELETED, keys);
Builder<SkyKey> unvisitedKeysBuilder = ImmutableList.builder();
for (SkyKey key : keys) {
if (visited.add(key)) {
unvisitedKeysBuilder.add(key);
}
}
ImmutableList<SkyKey> unvisitedKeys = unvisitedKeysBuilder.build();
for (SkyKey key : unvisitedKeys) {
pendingVisitations.add(Pair.of(key, InvalidationType.DELETED));
}
final Map<SkyKey, ? extends NodeEntry> entries =
graph.getBatch(null, Reason.INVALIDATION, unvisitedKeys);
for (final SkyKey key : unvisitedKeys) {
executor.execute(
new Runnable() {
@Override
public void run() {
NodeEntry entry = entries.get(key);
Pair<SkyKey, InvalidationType> invalidationPair =
Pair.of(key, InvalidationType.DELETED);
if (entry == null) {
pendingVisitations.remove(invalidationPair);
return;
}
if (traverseGraph) {
// Propagate deletion upwards.
visit(entry.getAllReverseDepsForNodeBeingDeleted(), InvalidationType.DELETED);
// Unregister this node as an rdep from its direct deps, since reverse dep
// edges cannot point to non-existent nodes. To know whether the child has this
// node as an "in-progress" rdep to be signaled, or just as a known rdep, we
// look at the deps that this node declared during its last (presumably
// interrupted) evaluation. If a dep is in this set, then it was notified to
// signal this node, and so the rdep will be an in-progress rdep, if the dep
// itself isn't done. Otherwise it will be a normal rdep. That information is
// used to remove this node as an rdep from the correct list of rdeps in the
// child -- because of our compact storage of rdeps, checking which list
// contains this parent could be expensive.
Set<SkyKey> signalingDeps =
entry.isDone()
? ImmutableSet.<SkyKey>of()
: entry.getTemporaryDirectDeps().toSet();
Iterable<SkyKey> directDeps;
try {
directDeps =
entry.isDone()
? entry.getDirectDeps()
: entry.getAllDirectDepsForIncompleteNode();
} catch (InterruptedException e) {
throw new IllegalStateException(
"Deletion cannot happen on a graph that may have blocking operations: "
+ key
+ ", "
+ entry,
e);
}
Map<SkyKey, ? extends NodeEntry> depMap =
graph.getBatch(key, Reason.INVALIDATION, directDeps);
for (Map.Entry<SkyKey, ? extends NodeEntry> directDepEntry : depMap.entrySet()) {
NodeEntry dep = directDepEntry.getValue();
if (dep != null) {
if (dep.isDone() || !signalingDeps.contains(directDepEntry.getKey())) {
try {
dep.removeReverseDep(key);
} catch (InterruptedException e) {
throw new IllegalStateException(
"Deletion cannot happen on a graph that may have blocking "
+ "operations: "
+ key
+ ", "
+ entry,
e);
}
} else {
// This step is not strictly necessary, since all in-progress nodes are
// deleted during graph cleaning, which happens in a single
// DeletingNodeVisitor visitation, aka the one right now. We leave this
// here in case the logic changes.
dep.removeInProgressReverseDep(key);
}
}
}
}
// Allow custom key-specific logic to update dirtiness status.
progressReceiver.invalidated(
key, EvaluationProgressReceiver.InvalidationState.DELETED);
// Actually remove the node.
graph.remove(key);
// Remove the node from the set as the last operation.
pendingVisitations.remove(invalidationPair);
}
});
}
}
}
/** A node-dirtying implementation. */
static class DirtyingNodeVisitor extends InvalidatingNodeVisitor<QueryableGraph> {
private final Set<SkyKey> changed =
Collections.newSetFromMap(
new ConcurrentHashMap<SkyKey, Boolean>(
EXPECTED_VISITED_SET_SIZE, .75f, DEFAULT_THREAD_COUNT));
private final Set<SkyKey> dirtied =
Collections.newSetFromMap(
new ConcurrentHashMap<SkyKey, Boolean>(
EXPECTED_VISITED_SET_SIZE, .75f, DEFAULT_THREAD_COUNT));
private final boolean supportInterruptions;
protected DirtyingNodeVisitor(
QueryableGraph graph,
DirtyTrackingProgressReceiver progressReceiver,
InvalidationState state,
Function<ExecutorParams, ? extends ExecutorService> executorFactory) {
super(graph, progressReceiver, state, executorFactory);
this.supportInterruptions = true;
}
/**
* Use cases that do not require support for interruptibility can avoid unnecessary work by
* passing {@code false} for {@param supportInterruptions}.
*/
protected DirtyingNodeVisitor(
QueryableGraph graph,
DirtyTrackingProgressReceiver progressReceiver,
InvalidationState state,
ForkJoinPool forkJoinPool,
boolean supportInterruptions) {
super(graph, progressReceiver, state, forkJoinPool);
this.supportInterruptions = supportInterruptions;
}
@Override
protected boolean getSupportInterruptions() {
return supportInterruptions;
}
@Override
void visit(Iterable<SkyKey> keys, InvalidationType invalidationType) {
Preconditions.checkState(invalidationType != InvalidationType.DELETED, keys);
visit(keys, invalidationType, null);
}
/**
* Queues a task to dirty the nodes named by {@param keys}. May be called from multiple threads.
* It is possible that the same node is enqueued many times. However, we require that a node
* is only actually marked dirty/changed once, with two exceptions:
*
* (1) If a node is marked dirty, it can subsequently be marked changed. This can occur if, for
* instance, FileValue workspace/foo/foo.cc is marked dirty because FileValue workspace/foo is
* marked changed (and every FileValue depends on its parent). Then FileValue
* workspace/foo/foo.cc is itself changed (this can even happen on the same build).
*
* (2) If a node is going to be marked both dirty and changed, as, for example, in the previous
* case if both workspace/foo/foo.cc and workspace/foo have been changed in the same build, the
* thread marking workspace/foo/foo.cc dirty may race with the one marking it changed, and so
* try to mark it dirty after it has already been marked changed. In that case, the
* {@link NodeEntry} ignores the second marking.
*
* The invariant that we do not process a (SkyKey, InvalidationType) pair twice is enforced by
* the {@link #changed} and {@link #dirtied} sets.
*
* The "invariant" is also enforced across builds by checking to see if the entry is already
* marked changed, or if it is already marked dirty and we are just going to mark it dirty
* again.
*
* If either of the above tests shows that we have already started a task to mark this entry
* dirty/changed, or that it is already marked dirty/changed, we do not continue this task.
*/
@ThreadSafe
private void visit(
Iterable<SkyKey> keys,
final InvalidationType invalidationType,
@Nullable SkyKey enqueueingKeyForExistenceCheck) {
final boolean isChanged = (invalidationType == InvalidationType.CHANGED);
Set<SkyKey> setToCheck = isChanged ? changed : dirtied;
int size = Iterables.size(keys);
ArrayList<SkyKey> keysToGet = new ArrayList<>(size);
for (SkyKey key : keys) {
if (setToCheck.add(key)) {
keysToGet.add(key);
}
}
if (supportInterruptions) {
for (SkyKey key : keysToGet) {
pendingVisitations.add(Pair.of(key, invalidationType));
}
}
final Map<SkyKey, ? extends ThinNodeEntry> entries;
try {
entries = graph.getBatch(null, Reason.INVALIDATION, keysToGet);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
// This can only happen if the main thread has been interrupted, and so the
// AbstractQueueVisitor is shutting down. We haven't yet removed the pending visitations, so
// we can resume next time.
return;
}
if (enqueueingKeyForExistenceCheck != null && entries.size() != keysToGet.size()) {
Set<SkyKey> missingKeys = Sets.difference(ImmutableSet.copyOf(keysToGet), entries.keySet());
throw new IllegalStateException(
String.format(
"key(s) %s not in the graph, but enqueued for dirtying by %s",
Iterables.limit(missingKeys, 10), enqueueingKeyForExistenceCheck));
}
for (final SkyKey key : keysToGet) {
executor.execute(
new Runnable() {
@Override
public void run() {
ThinNodeEntry entry = entries.get(key);
if (entry == null) {
if (supportInterruptions) {
pendingVisitations.remove(Pair.of(key, invalidationType));
}
return;
}
if (entry.isChanged() || (!isChanged && entry.isDirty())) {
// If this node is already marked changed, or we are only marking this node
// dirty, and it already is, move along.
if (supportInterruptions) {
pendingVisitations.remove(Pair.of(key, invalidationType));
}
return;
}
// It is not safe to interrupt the logic from this point until the end of the
// method.
// Any exception thrown should be unrecoverable.
// This entry remains in the graph in this dirty state until it is re-evaluated.
MarkedDirtyResult markedDirtyResult = null;
try {
markedDirtyResult = entry.markDirty(isChanged);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
// This can only happen if the main thread has been interrupted, and so the
// AbstractQueueVisitor is shutting down. We haven't yet removed the pending
// visitation, so we can resume next time.
return;
}
if (markedDirtyResult == null) {
// Another thread has already dirtied this node. Don't do anything in this thread.
if (supportInterruptions) {
pendingVisitations.remove(Pair.of(key, invalidationType));
}
return;
}
// Propagate dirtiness upwards and mark this node dirty/changed. Reverse deps should
// only be marked dirty (because only a dependency of theirs has changed).
visit(markedDirtyResult.getReverseDepsUnsafe(), InvalidationType.DIRTIED, key);
progressReceiver.invalidated(key,
EvaluationProgressReceiver.InvalidationState.DIRTY);
// Remove the node from the set as the last operation.
if (supportInterruptions) {
pendingVisitations.remove(Pair.of(key, invalidationType));
}
}
});
}
}
}
}