| // Copyright 2017 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.query2.engine; |
| |
| import com.google.common.collect.ImmutableList; |
| import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe; |
| |
| /** |
| * A helper for deduping values that have already been seen at certain "depths". |
| * |
| * <p>This is similar to {@link Uniquifier}. |
| */ |
| @ThreadSafe |
| public interface MinDepthUniquifier<T> { |
| |
| /** |
| * Returns whether {@code newElement} hasn't been seen before at depth less than or equal to |
| * {@code depth} by {@link #uniqueAtDepthLessThanOrEqualTo(T, int)} or |
| * {@link #uniqueAtDepthLessThanOrEqualTo(Iterable, int)}. |
| * |
| * <p>Please note the difference between this method and |
| * {@link #uniqueAtDepthLessThanOrEqualTo(T, int)}! |
| * |
| * <p>This method is inherently racy wrt {@link #uniqueAtDepthLessThanOrEqualTo(T, int)} and |
| * {@link #uniqueAtDepthLessThanOrEqualTo(Iterable, int)}. Only use it if you know what you are |
| * doing. |
| */ |
| boolean uniqueAtDepthLessThanOrEqualToPure(T newElement, int depth); |
| |
| /** |
| * Returns whether {@code newElement} hasn't been seen before at depth less than or equal to |
| * {@code depth} by {@link #uniqueAtDepthLessThanOrEqualTo(T, int)} or |
| * {@link #uniqueAtDepthLessThanOrEqualTo(Iterable, int)}. |
| * |
| * <p> There's a natural benign check-then-act race in all concurrent uses of this interface. |
| * Imagine we have an element e, two depths d1 and d2 (with d2 < d1), and two threads T1 and T2. |
| * T1 may think it's about to be the first one to process e at a depth less than or equal to d1. |
| * But before T1 finishes processing e, T2 may think _it's_ about to be first one to process an |
| * element at a depth less than or equal to than d2. T1's work is probably wasted. |
| */ |
| boolean uniqueAtDepthLessThanOrEqualTo(T newElement, int depth); |
| |
| /** |
| * Batch version of {@link #uniqueAtDepthLessThanOrEqualTo(Object, int)}. |
| * |
| * <p>The same benign check-then-act race applies here too. |
| */ |
| ImmutableList<T> uniqueAtDepthLessThanOrEqualTo(Iterable<T> newElements, int depth); |
| } |
| |