src/main/java/com/google/devtools/build/lib/runtime/CriticalPathComputer.java

// 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.runtime;

import com.google.common.base.Preconditions;
import com.google.common.collect.Comparators;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Maps;
import com.google.common.eventbus.AllowConcurrentEvents;
import com.google.common.eventbus.Subscribe;
import com.google.devtools.build.lib.actions.Action;
import com.google.devtools.build.lib.actions.ActionAnalysisMetadata;
import com.google.devtools.build.lib.actions.ActionCompletionEvent;
import com.google.devtools.build.lib.actions.ActionKeyContext;
import com.google.devtools.build.lib.actions.ActionMiddlemanEvent;
import com.google.devtools.build.lib.actions.ActionRewoundEvent;
import com.google.devtools.build.lib.actions.ActionStartedEvent;
import com.google.devtools.build.lib.actions.Actions;
import com.google.devtools.build.lib.actions.Artifact;
import com.google.devtools.build.lib.actions.CachedActionEvent;
import com.google.devtools.build.lib.actions.DiscoveredInputsEvent;
import com.google.devtools.build.lib.actions.SpawnExecutedEvent;
import com.google.devtools.build.lib.actions.SpawnMetrics;
import com.google.devtools.build.lib.actions.SpawnResult;
import com.google.devtools.build.lib.clock.Clock;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.BinaryOperator;
import java.util.stream.Stream;
import javax.annotation.concurrent.ThreadSafe;

/**
 * Computes the critical path in the action graph based on events published to the event bus.
 *
 * <p>After instantiation, this object needs to be registered on the event bus to work.
 */
@ThreadSafe
public class CriticalPathComputer {
  /** Number of top actions to record. */
  static final int SLOWEST_COMPONENTS_SIZE = 30;
  private static final int LARGEST_MEMORY_COMPONENTS_SIZE = 20;
  private static final int LARGEST_INPUT_SIZE_COMPONENTS_SIZE = 20;

  /** Selects and returns the longer of two components (the first may be {@code null}). */
  private static final BinaryOperator<CriticalPathComponent> SELECT_LONGER_COMPONENT =
      (a, b) ->
          a == null || a.getAggregatedElapsedTime().compareTo(b.getAggregatedElapsedTime()) < 0
              ? b
              : a;

  private final AtomicInteger idGenerator = new AtomicInteger();
  // outputArtifactToComponent is accessed from multiple event handlers.
  private final ConcurrentMap<Artifact, CriticalPathComponent> outputArtifactToComponent =
      Maps.newConcurrentMap();
  private final ActionKeyContext actionKeyContext;

  /** Maximum critical path found. */
  private final AtomicReference<CriticalPathComponent> maxCriticalPath;
  private final Clock clock;
  private final boolean checkCriticalPathInconsistencies;

  public CriticalPathComputer(
      ActionKeyContext actionKeyContext, Clock clock, boolean checkCriticalPathInconsistencies) {
    this.actionKeyContext = actionKeyContext;
    this.clock = clock;
    maxCriticalPath = new AtomicReference<>();
    this.checkCriticalPathInconsistencies = checkCriticalPathInconsistencies;
  }

  public CriticalPathComputer(ActionKeyContext actionKeyContext, Clock clock) {
    this(actionKeyContext, clock, /*checkCriticalPathInconsistencies=*/ true);
  }

  /**
   * Creates a critical path component for an action.
   *
   * @param action the action for the critical path component
   * @param relativeStartNanos time when the action started to run in nanos. Only meant to be used
   *     for computing time differences.
   */
  private CriticalPathComponent createComponent(Action action, long relativeStartNanos) {
    return new CriticalPathComponent(idGenerator.getAndIncrement(), action, relativeStartNanos);
  }

  /**
   * Return the critical path stats for the current command execution.
   *
   * <p>This method allows us to calculate lazily the aggregate statistics of the critical path,
   * avoiding the memory and cpu penalty for doing it for all the actions executed.
   */
  public AggregatedCriticalPath aggregate() {
    CriticalPathComponent criticalPath = getMaxCriticalPath();
    if (criticalPath == null) {
      return AggregatedCriticalPath.EMPTY;
    }

    ImmutableList.Builder<CriticalPathComponent> components = ImmutableList.builder();
    ImmutableList.Builder<SpawnMetrics> metrics = ImmutableList.builder();
    CriticalPathComponent child = criticalPath;

    while (child != null) {
      SpawnMetrics childSpawnMetrics = child.getSpawnMetrics();
      if (childSpawnMetrics != null) {
        metrics.add(childSpawnMetrics);
      }
      components.add(child);
      child = child.getChild();
    }

    return new AggregatedCriticalPath(
        criticalPath.getAggregatedElapsedTime(),
        SpawnMetrics.aggregateMetrics(metrics.build(), false),
        components.build());
  }

  public Map<Artifact, CriticalPathComponent> getCriticalPathComponentsMap() {
    return outputArtifactToComponent;
  }

  /** Changes the phase of the action */
  @Subscribe
  @AllowConcurrentEvents
  public void nextCriticalPathPhase(SpawnExecutedEvent.ChangePhase phase) {
    CriticalPathComponent stats =
        outputArtifactToComponent.get(phase.getAction().getPrimaryOutput());
    if (stats != null) {
      stats.changePhase();
    }
  }

  /** Adds spawn metrics to the action stats. */
  @Subscribe
  @AllowConcurrentEvents
  public void spawnExecuted(SpawnExecutedEvent event) {
    ActionAnalysisMetadata action = event.getActionMetadata();
    Artifact primaryOutput = action.getPrimaryOutput();
    if (primaryOutput == null) {
      // Despite the documentation to the contrary, the SpawnIncludeScanner creates an
      // ActionExecutionMetadata instance that returns a null primary output. That said, this
      // class is incorrect wrt. multiple Spawns in a single action. See b/111583707.
      return;
    }
    CriticalPathComponent stats =
        Preconditions.checkNotNull(outputArtifactToComponent.get(primaryOutput));

    SpawnResult spawnResult = event.getSpawnResult();
    stats.addSpawnResult(
        spawnResult.getMetrics(), spawnResult.getRunnerName(), spawnResult.wasRemote());
  }

  /** Returns the list of components using the most memory. */
  public List<CriticalPathComponent> getLargestMemoryComponents() {
    return uniqueActions()
        .collect(
            Comparators.greatest(
                LARGEST_MEMORY_COMPONENTS_SIZE,
                Comparator.comparingLong((c) -> c.getSpawnMetrics().memoryEstimate())));
  }

  /** Returns the list of components with the largest input sizes. */
  public List<CriticalPathComponent> getLargestInputSizeComponents() {
    return uniqueActions()
        .collect(
            Comparators.greatest(
                LARGEST_INPUT_SIZE_COMPONENTS_SIZE,
                Comparator.comparingLong((c) -> c.getSpawnMetrics().inputBytes())));
  }

  /** Returns the list of slowest components. */
  public List<CriticalPathComponent> getSlowestComponents() {
    return uniqueActions()
        .collect(
            Comparators.greatest(
                SLOWEST_COMPONENTS_SIZE,
                Comparator.comparingLong(CriticalPathComponent::getElapsedTimeNanos)));
  }

  private Stream<CriticalPathComponent> uniqueActions() {
    return outputArtifactToComponent.entrySet().stream()
        .filter((e) -> e.getValue().isPrimaryOutput(e.getKey()))
        .map((e) -> e.getValue());
  }

  /** Creates a CriticalPathComponent and adds the duration of input discovery and changes phase. */
  @Subscribe
  @AllowConcurrentEvents
  public void discoverInputs(DiscoveredInputsEvent event) {
    CriticalPathComponent stats =
        tryAddComponent(createComponent(event.getAction(), event.getStartTimeNanos()));
    stats.addSpawnResult(event.getMetrics(), null, /* wasRemote=*/ false);
    stats.changePhase();
  }

  /**
   * Record an action that has started to run. If the CriticalPathComponent has not been created,
   * initialize it and then start running.
   *
   * @param event information about the started action
   */
  @Subscribe
  @AllowConcurrentEvents
  public void actionStarted(ActionStartedEvent event) {
    Action action = event.getAction();
    tryAddComponent(createComponent(action, event.getNanoTimeStart())).startRunning();
  }

  /**
   * Record a middleman action execution. Even if middleman are almost instant, we record them
   * because they depend on other actions and we need them for constructing the critical path.
   *
   * <p>For some rules with incorrect configuration transitions we might get notified several times
   * for the same middleman. This should only happen if the actions are shared.
   */
  @Subscribe
  @AllowConcurrentEvents
  public void middlemanAction(ActionMiddlemanEvent event) {
    Action action = event.getAction();
    CriticalPathComponent component =
        tryAddComponent(createComponent(action, event.getNanoTimeStart()));
    finalizeActionStat(event.getNanoTimeStart(), action, component);
  }

  /**
   * Try to add the component to the map of critical path components. If there is an existing
   * component for its primary output it uses that to update the rest of the outputs.
   *
   * @return The component to be used for updating the time stats.
   */
  @SuppressWarnings("ReferenceEquality")
  private CriticalPathComponent tryAddComponent(CriticalPathComponent newComponent) {
    Action newAction = newComponent.getAction();
    Artifact primaryOutput = newAction.getPrimaryOutput();
    CriticalPathComponent storedComponent =
        outputArtifactToComponent.putIfAbsent(primaryOutput, newComponent);
    if (storedComponent != null) {
      Action oldAction = storedComponent.getAction();
      // TODO(b/120663721) Replace this fragile reference equality check with something principled.
      if (oldAction != newAction && !Actions.canBeShared(actionKeyContext, newAction, oldAction)) {
        throw new IllegalStateException(
            "Duplicate output artifact found for unsharable actions."
                + "This can happen if a previous event registered the action.\n"
                + "Old action: "
                + oldAction
                + "\n\nNew action: "
                + newAction
                + "\n\nArtifact: "
                + primaryOutput
                + "\n");
      }
    } else {
      storedComponent = newComponent;
    }
    // Try to insert the existing component for the rest of the outputs even if we failed to be
    // the ones inserting the component so that at the end of this method we guarantee that all the
    // outputs have a component.
    for (Artifact output : newAction.getOutputs()) {
      if (output == primaryOutput) {
        continue;
      }
      CriticalPathComponent old = outputArtifactToComponent.putIfAbsent(output, storedComponent);
      // If two actions run concurrently maybe we find a component by primary output but we are
      // the first updating the rest of the outputs.
      Preconditions.checkState(
          old == null || old == storedComponent, "Inconsistent state for %s", newAction);
    }
    return storedComponent;
  }

  /**
   * Record an action that was not executed because it was in the (disk) cache. This is needed so
   * that we can calculate correctly the dependencies tree if we have some cached actions in the
   * middle of the critical path.
   */
  @Subscribe
  @AllowConcurrentEvents
  public void actionCached(CachedActionEvent event) {
    Action action = event.getAction();
    CriticalPathComponent component =
        tryAddComponent(createComponent(action, event.getNanoTimeStart()));
    finalizeActionStat(event.getNanoTimeStart(), action, component);
  }

  /**
   * Records the elapsed time stats for the action. For each input artifact, it finds the real
   * dependent artifacts and records the critical path stats.
   */
  @Subscribe
  @AllowConcurrentEvents
  public void actionComplete(ActionCompletionEvent event) {
    Action action = event.getAction();
    CriticalPathComponent component =
        Preconditions.checkNotNull(
            outputArtifactToComponent.get(action.getPrimaryOutput()), action);
    finalizeActionStat(event.getRelativeActionStartTime(), action, component);
  }

  /**
   * Record that the failed rewound action is no longer running. The action may or may not start
   * again later.
   */
  @Subscribe
  @AllowConcurrentEvents
  public void actionRewound(ActionRewoundEvent event) {
    Action action = event.getFailedRewoundAction();
    CriticalPathComponent component =
        Preconditions.checkNotNull(outputArtifactToComponent.get(action.getPrimaryOutput()));
    component.finishActionExecution(event.getRelativeActionStartTime(), clock.nanoTime());
  }

  /** Maximum critical path component found during the build. */
  protected CriticalPathComponent getMaxCriticalPath() {
    return maxCriticalPath.get();
  }

  private void finalizeActionStat(
      long startTimeNanos, Action action, CriticalPathComponent component) {
    long finishTimeNanos = clock.nanoTime();
    for (Artifact input : action.getInputs().toList()) {
      addArtifactDependency(component, input, finishTimeNanos);
    }
    component.finishActionExecution(startTimeNanos, finishTimeNanos);
    maxCriticalPath.accumulateAndGet(component, SELECT_LONGER_COMPONENT);
  }

  /** If "input" is a generated artifact, link its critical path to the one we're building. */
  private void addArtifactDependency(
      CriticalPathComponent actionStats, Artifact input, long componentFinishNanos) {
    CriticalPathComponent depComponent = outputArtifactToComponent.get(input);
    if (depComponent != null) {
      if (depComponent.isRunning()) {
        checkCriticalPathInconsistency(
            (Artifact.DerivedArtifact) input, depComponent.getAction(), actionStats);
        return;
      }
      actionStats.addDepInfo(depComponent, componentFinishNanos);
    }
  }

  private void checkCriticalPathInconsistency(
      Artifact.DerivedArtifact input, Action dependencyAction, CriticalPathComponent actionStats) {
    if (!checkCriticalPathInconsistencies) {
      return;
    }
    // Rare case that an action depending on a previously-cached shared action sees a different
    // shared action that is in the midst of being an action cache hit.
    for (Artifact actionOutput : dependencyAction.getOutputs()) {
      if (input.equals(actionOutput)
          && input
              .getGeneratingActionKey()
              .equals(((Artifact.DerivedArtifact) actionOutput).getGeneratingActionKey())) {
        // This (currently running) dependency action is the same action that produced the input for
        // the finished actionStats CriticalPathComponent. This should be impossible.
        throw new IllegalStateException(
            String.format(
                "Cannot add critical path stats when the dependency action is not finished. "
                    + "%s. %s. %s.",
                input, actionStats.prettyPrintAction(), dependencyAction));
      }
    }
  }
}