chromium/third_party/abseil-cpp/absl/profiling/internal/periodic_sampler.h

// Copyright 2019 The Abseil Authors.
//
// 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
//
//      https://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 ABSL_PROFILING_INTERNAL_PERIODIC_SAMPLER_H_
#define ABSL_PROFILING_INTERNAL_PERIODIC_SAMPLER_H_

#include <stdint.h>

#include <atomic>

#include "absl/base/optimization.h"
#include "absl/profiling/internal/exponential_biased.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace profiling_internal {

// PeriodicSamplerBase provides the basic period sampler implementation.
//
// This is the base class for the templated PeriodicSampler class, which holds
// a global std::atomic value identified by a user defined tag, such that
// each specific PeriodSampler implementation holds its own global period.
//
// PeriodicSamplerBase is thread-compatible except where stated otherwise.
class PeriodicSamplerBase { … };

inline bool PeriodicSamplerBase::SubtleMaybeSample() noexcept { … }

inline bool PeriodicSamplerBase::Sample() noexcept { … }

// PeriodicSampler is a concreted periodic sampler implementation.
// The user provided Tag identifies the implementation, and is required to
// isolate the global state of this instance from other instances.
//
// Typical use case:
//
//   struct HashTablezTag {};
//   thread_local PeriodicSampler<HashTablezTag, 100> sampler;
//
//   void HashTableSamplingLogic(...) {
//     if (sampler.Sample()) {
//       HashTableSlowSamplePath(...);
//     }
//   }
//
template <typename Tag, int default_period = 0>
class PeriodicSampler final : public PeriodicSamplerBase { … };

template <typename Tag, int default_period>
std::atomic<int> PeriodicSampler<Tag, default_period>::period_(default_period);

}  // namespace profiling_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_PROFILING_INTERNAL_PERIODIC_SAMPLER_H_