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// Copyright 2019 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.devtools.build.lib.actions.ActionExecutionException;
import com.google.devtools.build.skyframe.SkyFunction;
import com.google.devtools.build.skyframe.SkyKey;
import com.google.devtools.build.skyframe.SkyValue;
import com.google.devtools.build.skyframe.ValueOrException2;
import java.io.IOException;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
/**
* A builder of values for {@link ArtifactNestedSetKey}.
*
* <p>When an Action is executed with ActionExecutionFunction, the actions's input {@code
* NestedSet<Artifact>} could be evaluated as an {@link ArtifactNestedSetKey}[1].
*
* <p>{@link ArtifactNestedSetFunction} then evaluates the {@link ArtifactNestedSetKey} by:
*
* <p>- Evaluating the directs elements as Artifacts. Commit the result into artifactToSkyValueMap.
*
* <p>- Evaluating the transitive elements as {@link ArtifactNestedSetKey}s.
*
* <p>ActionExecutionFunction can then access this map to get the Artifacts' values.
*
* <p>[1] Heuristic: If the size of the NestedSet exceeds a certain threshold, we evaluate it as an
* ArtifactNestedSetKey.
*/
class ArtifactNestedSetFunction implements SkyFunction {
/**
* A concurrent map from Artifacts' SkyKeys to their ValueOrException, for Artifacts that are part
* of NestedSets which were evaluated as {@link ArtifactNestedSetKey}.
*
* <p>Question: Why don't we clear artifactToSkyValueMap after each build?
*
* <p>The map maintains an invariant: if an ArtifactNestedSetKey exists on Skyframe, the SkyValues
* of its member Artifacts are available in artifactToSkyValueMap.
*
* <p>Example: Action A has as input NestedSet X, where X = (X1, X2), where X1 & X2 are 2
* transitive NestedSets.
*
* <p>Run 0: Establish dependency from A to X and from X to X1 & X2. Artifacts from X1 & X2 have
* entries in artifactToSkyValueMap.
*
* <p>Run 1 (incremental): Some changes were made to an Artifact in X1 such that X1, X and A's
* SkyKeys are marked as dirty. A's ActionLookupData has to be re-evaluated. This involves asking
* Skyframe to compute SkyValues for its inputs.
*
* <p>However, X2 is not dirty, so Skyframe won't re-run ArtifactNestedSetFunction#compute for X2,
* therefore not populating artifactToSkyValueMap with X2's member Artifacts. Hence if we clear
* artifactToSkyValueMap between build 0 and 1, X2's member artifacts' SkyValues would not be
* available in the map.
*
* <p>Keeping the map in between builds introduces a potential memory leak: if an Artifact is no
* longer valid, it would still exist in the map. TODO(leba): Address this memory leak if it
* causes serious regression.
*/
private final ConcurrentMap<SkyKey, ValueOrException2<IOException, ActionExecutionException>>
artifactToSkyValueMap;
private static ArtifactNestedSetFunction singleton = null;
private ArtifactNestedSetFunction() {
artifactToSkyValueMap = new ConcurrentHashMap<>();
}
@Override
public SkyValue compute(SkyKey skyKey, Environment env) throws InterruptedException {
ArtifactNestedSetKey artifactNestedSetKey = (ArtifactNestedSetKey) skyKey;
Map<SkyKey, ValueOrException2<IOException, ActionExecutionException>>
directArtifactsEvalResult =
env.getValuesOrThrow(
artifactNestedSetKey.directKeys(),
IOException.class,
ActionExecutionException.class);
if (env.valuesMissing()) {
return null;
}
// Evaluate all children.
env.getValues(artifactNestedSetKey.transitiveKeys());
if (env.valuesMissing()) {
return null;
}
// Only commit to the map when every value is present.
artifactToSkyValueMap.putAll(directArtifactsEvalResult);
return ArtifactNestedSetValue.createOrGetInstance();
}
public static ArtifactNestedSetFunction getInstance() {
if (singleton == null) {
singleton = new ArtifactNestedSetFunction();
}
return singleton;
}
Map<SkyKey, ValueOrException2<IOException, ActionExecutionException>> getArtifactToSkyValueMap() {
return artifactToSkyValueMap;
}
@Override
public String extractTag(SkyKey skyKey) {
return null;
}
}