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// Copyright 2015 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.Optional;
import com.google.common.base.Preconditions;
import com.google.devtools.build.lib.util.io.TimestampGranularityMonitor;
import com.google.devtools.build.skyframe.SkyKey;
import com.google.devtools.build.skyframe.SkyValue;
import javax.annotation.Nullable;
/**
* Given a {@link SkyKey} and the previous {@link SkyValue} it had, returns whether this value is
* up to date.
*/
public abstract class SkyValueDirtinessChecker {
/**
* Returns
* <ul>
* <li>{@code null}, if the checker can't handle {@code key}.
* <li>{@code Optional.<SkyValue>absent()} if the checker can handle {@code key} but was unable
* to create a new value.
* <li>{@code Optional.<SkyValue>of(v)} if the checker can handle {@code key} and the new value
* should be {@code v}.
* </ul>
*/
@Nullable
public abstract Optional<SkyValue> maybeCreateNewValue(SkyKey key,
TimestampGranularityMonitor tsgm);
/**
* Returns the result of checking whether this key's value is up to date, or null if this
* dirtiness checker does not apply to this key. If non-null, this answer is assumed to be
* definitive.
*/
@Nullable
public DirtyResult maybeCheck(SkyKey key, @Nullable SkyValue oldValue,
TimestampGranularityMonitor tsgm) {
Optional<SkyValue> newValueMaybe = maybeCreateNewValue(key, tsgm);
if (newValueMaybe == null) {
return null;
}
if (!newValueMaybe.isPresent()) {
return DirtyResult.dirty(oldValue);
}
SkyValue newValue = Preconditions.checkNotNull(newValueMaybe.get(), key);
return newValue.equals(oldValue)
? DirtyResult.notDirty(oldValue)
: DirtyResult.dirtyWithNewValue(oldValue, newValue);
}
/** An encapsulation of the result of checking to see if a value is up to date. */
public static class DirtyResult {
/**
* Creates a DirtyResult indicating that the external value is the same as the value in the
* graph.
*/
public static DirtyResult notDirty(SkyValue oldValue) {
return new DirtyResult(/*dirty=*/false, oldValue, /*newValue=*/null);
}
/**
* Creates a DirtyResult indicating that external value is different from the value in the
* graph, but this new value is not known.
*/
public static DirtyResult dirty(@Nullable SkyValue oldValue) {
return new DirtyResult(/*dirty=*/true, oldValue, /*newValue=*/null);
}
/**
* Creates a DirtyResult indicating that the external value is {@code newValue}, which is
* different from the value in the graph,
*/
public static DirtyResult dirtyWithNewValue(@Nullable SkyValue oldValue, SkyValue newValue) {
return new DirtyResult(/*dirty=*/true, oldValue, newValue);
}
private final boolean isDirty;
@Nullable private final SkyValue oldValue;
@Nullable private final SkyValue newValue;
private DirtyResult(boolean isDirty, @Nullable SkyValue oldValue,
@Nullable SkyValue newValue) {
this.isDirty = isDirty;
this.oldValue = oldValue;
this.newValue = newValue;
}
boolean isDirty() {
return isDirty;
}
@Nullable
SkyValue getOldValue() {
return oldValue;
}
/**
* If {@code isDirty()}, then either returns the new value for the value or {@code null} if
* the new value wasn't computed. In the case where the value is dirty and a new value is
* available, then the new value can be injected into the skyframe graph. Otherwise, the value
* should simply be invalidated.
*/
@Nullable
SkyValue getNewValue() {
Preconditions.checkState(isDirty(), newValue);
return newValue;
}
}
}
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