chromium/third_party/perfetto/include/perfetto/base/flat_set.h

/*
 * Copyright (C) 2019 The Android Open Source Project
 *
 * 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.
 */

#ifndef INCLUDE_PERFETTO_BASE_FLAT_SET_H_
#define INCLUDE_PERFETTO_BASE_FLAT_SET_H_

#include <algorithm>
#include <vector>

// A vector-based set::set-like container.
// It's more cache friendly than std::*set and performs for cases where:
// 1. A high number of dupes is expected (e.g. pid tracking in ftrace).
// 2. The working set is small (hundreds of elements).

// Performance characteristics (for uniformly random insertion order):
// - For smaller insertions (up to ~500), it outperforms both std::set<int> and
//   std::unordered_set<int> by ~3x.
// - Up until 4k insertions, it is always faster than std::set<int>.
// - unordered_set<int> is faster with more than 2k insertions.
// - unordered_set, however, it's less memory efficient and has more caveats
//   (see chromium's base/containers/README.md).
//
// See flat_set_benchmark.cc and the charts in go/perfetto-int-set-benchmark.

namespace perfetto {
namespace base {

template <typename T>
class FlatSet { … };

}  // namespace base
}  // namespace perfetto

#endif  // INCLUDE_PERFETTO_BASE_FLAT_SET_H_