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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 java.util.Collection;
/**
* NestedSetVisitor facilitates a transitive visitation over a NestedSet. 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.
*
* @param <E> the data type
*/
public final class NestedSetVisitor<E> {
/**
* For each element of the NestedSet the {@code Receiver} will receive one element during the
* visitation.
*/
public interface Receiver<E> {
void accept(E arg);
}
private final Receiver<E> callback;
private final VisitedState visited;
public NestedSetVisitor(Receiver<E> callback, VisitedState visited) {
this.callback = Preconditions.checkNotNull(callback);
this.visited = Preconditions.checkNotNull(visited);
}
/**
* Transitively visit a nested set.
*
* @param nestedSet the nested set to visit transitively.
*/
public void visit(NestedSet<E> nestedSet) throws InterruptedException {
// We can short-circuit empty nested set visitation here, avoiding load on the shared map
// VisitedState#seenNodes.
if (!nestedSet.isEmpty()) {
visitRaw(nestedSet.getChildrenInterruptibly());
}
}
/** Visit every entry in a collection. */
public void visit(Collection<E> collection) {
for (E e : collection) {
if (visited.add(e)) {
callback.accept(e);
}
}
}
@SuppressWarnings("unchecked")
private void visitRaw(Object node) {
if (visited.add(node)) {
if (node instanceof Object[]) {
for (Object child : (Object[]) node) {
visitRaw(child);
}
} else {
callback.accept((E) node);
}
}
}
/** Allows {@link NestedSetVisitor} to keep track of the seen nodes and transitive sets. */
public interface VisitedState {
/**
* Adds a node to the visited state, returning true if the node was not yet in the visited state
* and false if the node was already in the visited state.
*/
boolean add(Object node);
}
}