// 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". * *
This is similar to {@link Uniquifier}.
*/
@ThreadSafe
public interface MinDepthUniquifier 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.
*/
ImmutableList