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// 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.collect.nestedset;
import com.google.common.base.Preconditions;
import com.google.common.collect.Sets;
import java.util.Set;
/**
* NestedSetVisitor facilitates a transitive visitation over a NestedSet, which must be in STABLE
* order. The callback may be called from multiple threads, and must be thread-safe.
*
* <p>The visitation is iterative: The caller may invoke a NestedSet within the top-level NestedSet
* in any order.
*
* <p>Currently this class is only used in Skyframe to facilitate iterative replay of transitive
* warnings/errors.
*
* @param <E> the data type
*/
// @ThreadSafety.ThreadSafe
public final class NestedSetVisitor<E> {
/**
* For each element of the NestedSet the {@code Reciver} will receive one element during the
* visitation.
*/
public interface Receiver<E> {
void accept(E arg);
}
private final Receiver<E> callback;
private final VisitedState<E> visited;
public NestedSetVisitor(Receiver<E> callback, VisitedState<E> visited) {
this.callback = Preconditions.checkNotNull(callback);
this.visited = Preconditions.checkNotNull(visited);
}
/**
* Transitively visit a nested set.
*
* @param nestedSet the nested set to visit transitively.
*
*/
@SuppressWarnings("unchecked")
public void visit(NestedSet<E> nestedSet) {
// This method suppresses the unchecked warning so that it can access the internal NestedSet
// raw structure.
Preconditions.checkArgument(nestedSet.getOrder() == Order.STABLE_ORDER);
if (!visited.add(nestedSet)) {
return;
}
for (NestedSet<E> subset : nestedSet.transitiveSets()) {
visit(subset);
}
for (Object member : nestedSet.directMembers()) {
if (visited.add((E) member)) {
callback.accept((E) member);
}
}
}
/** A class that allows us to keep track of the seen nodes and transitive sets. */
public static class VisitedState<E> {
private final Set<NestedSet<E>> seenSets = Sets.newConcurrentHashSet();
private final Set<E> seenNodes = Sets.newConcurrentHashSet();
public void clear() {
seenSets.clear();
seenNodes.clear();
}
private boolean add(E node) {
return seenNodes.add(node);
}
private boolean add(NestedSet<E> set) {
return !set.isEmpty() && seenSets.add(set);
}
}
}
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