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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.skyframe;
import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
import com.google.devtools.build.lib.util.Preconditions;
import javax.annotation.Nullable;
/**
* A node in the graph without the means to access its value. All operations on this class are
* thread-safe. Note, however, the warning on the return value of {@link #markDirty}.
*
* <p>This interface is public only for the benefit of alternative graph implementations outside of
* the package.
*/
public interface ThinNodeEntry {
/** Returns whether the entry has been built and is finished evaluating. */
@ThreadSafe
boolean isDone();
/**
* Returns true if the entry is marked dirty, meaning that at least one of its transitive
* dependencies is marked changed.
*/
@ThreadSafe
boolean isDirty();
/**
* Returns true if the entry is marked changed, meaning that it must be re-evaluated even if its
* dependencies' values have not changed.
*/
@ThreadSafe
boolean isChanged();
/**
* Marks this node dirty, or changed if {@code isChanged} is true. The node is put in the
* just-created state. It will be re-evaluated if necessary during the evaluation phase, but if it
* has not changed, it will not force a re-evaluation of its parents.
*
* <p>{@code markDirty(b)} must not be called on an undone node if {@code isChanged() == b}. It is
* the caller's responsibility to ensure that this does not happen. Calling {@code
* markDirty(false)} when {@code isChanged() == true} has no effect. The idea here is that the
* caller will only ever want to call {@code markDirty()} a second time if a transition from a
* dirty-unchanged state to a dirty-changed state is required.
*
* @return A {@link ThinNodeEntry.MarkedDirtyResult} if the node was previously clean, and {@code
* null} if it was already dirty. If it was already dirty, the caller should abort its
* handling of this node, since another thread is already dealing with it. Note the warning on
* {@link ThinNodeEntry.MarkedDirtyResult} regarding the collection it provides.
*/
@Nullable
@ThreadSafe
MarkedDirtyResult markDirty(boolean isChanged) throws InterruptedException;
/**
* Returned by {@link #markDirty} if that call changed the node from clean to dirty. Contains an
* iterable of the node's reverse deps for efficiency, because the single use case for {@link
* #markDirty} is during invalidation, and if such an invalidation call wins, the invalidator
* must immediately afterwards schedule the invalidation of the node's reverse deps.
*
* <p>Warning: {@link #getReverseDepsUnsafe()} may return a live view of the reverse deps
* collection of the marked-dirty node. The consumer of this data must be careful only to
* iterate over and consume its values while that collection is guaranteed not to change. This
* is true during invalidation, because reverse deps don't change during invalidation.
*/
class MarkedDirtyResult {
private final Iterable<SkyKey> reverseDepsUnsafe;
public MarkedDirtyResult(Iterable<SkyKey> reverseDepsUnsafe) {
this.reverseDepsUnsafe = Preconditions.checkNotNull(reverseDepsUnsafe);
}
public Iterable<SkyKey> getReverseDepsUnsafe() {
return reverseDepsUnsafe;
}
}
}
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