BackdownStrategy.h

/*
 * Copyright (C) 2020-2022 HERE Europe B.V.
 *
 * 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.
 *
 * SPDX-License-Identifier: Apache-2.0
 * License-Filename: LICENSE
 */
 
#pragma once
 
#include <algorithm>
#include <chrono>
#include <random>
 
#include <olp/core/CoreApi.h>
 
namespace olp {
namespace client {
 
struct CORE_API ExponentialBackdownStrategy {
 public:
  std::chrono::milliseconds operator()(
      std::chrono::milliseconds initial_backdown_period, size_t retry_count) {
    const auto exponential_wait_time =
        initial_backdown_period.count() * (size_t{1} << retry_count);
 
    static thread_local std::mt19937 kGenerator(std::random_device{}());
    std::uniform_int_distribution<std::chrono::milliseconds::rep> dist(
        0, exponential_wait_time);
    return std::chrono::milliseconds(dist(kGenerator));
  }
};
 
struct CORE_API EqualJitterBackdownStrategy {
 public:
  explicit EqualJitterBackdownStrategy(
      std::chrono::milliseconds cap = std::chrono::seconds(1))
      : cap_{cap} {}
 
  std::chrono::milliseconds operator()(
      std::chrono::milliseconds initial_backdown_period, size_t retry_count) {
    // make sure we don't overflow
    constexpr size_t max_retry_count = 30u;
    retry_count = std::min<size_t>(retry_count, max_retry_count);
    const int64_t exponential_wait_time =
        initial_backdown_period.count() * (1ull << retry_count);
    static thread_local std::mt19937 kGenerator(std::random_device{}());
    const auto temp = std::min<int64_t>(cap_.count(), exponential_wait_time);
    std::uniform_int_distribution<int64_t> dist(0, temp / 2);
    const auto sleep = temp / 2 + dist(kGenerator);
    return std::chrono::milliseconds(sleep);
  }
 
 private:
  std::chrono::milliseconds cap_;
};
 
}  // namespace client
}  // namespace olp