ThreadedRepeatingFunctionRunner.h

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/*
 * Copyright 2014-present Facebook, Inc.
 *
 * 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.
 */

#pragma once

#include <folly/Function.h>
#include <condition_variable>
#include <thread>
#include <vector>

namespace folly {

class ThreadedRepeatingFunctionRunner final {
 public:
  // Returns how long to wait before the next repetition. Must not throw.
  using RepeatingFn = folly::Function<std::chrono::milliseconds() noexcept>;

  ThreadedRepeatingFunctionRunner();
  ~ThreadedRepeatingFunctionRunner();

  void stop();

  void add(
      std::string name,
      RepeatingFn f,
      std::chrono::milliseconds initialSleep = std::chrono::milliseconds(0));

  size_t size() const {
    return threads_.size();
  }

 private:
  // Returns true if this is the first stop().
  bool stopImpl();

  // Sleep for a duration, or until stop() is called.
  bool waitFor(std::chrono::milliseconds duration) noexcept;

  // Noexcept allows us to get a good backtrace on crashes -- otherwise,
  // std::terminate would get called **outside** of the thread function.
  void executeInLoop(
      RepeatingFn,
      std::chrono::milliseconds initialSleep) noexcept;

  std::mutex stopMutex_;
  bool stopping_{false}; // protected by stopMutex_
  std::condition_variable stopCv_;

  std::vector<std::thread> threads_;
};

} // namespace folly