| // 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); |
| } |
| } |