folly/folly/io/async/TimerFD.h

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * 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

#if defined(__linux__) && !defined(__ANDROID__)
#define FOLLY_HAVE_TIMERFD
#endif

#include <folly/io/async/EventBase.h>
#ifdef FOLLY_HAVE_TIMERFD
#include <folly/io/async/EventHandler.h>
#else
#include <folly/io/async/AsyncTimeout.h>
#endif
#include <chrono>

namespace folly {
#ifdef FOLLY_HAVE_TIMERFD
// timerfd wrapper
class TimerFD : public folly::EventHandler,
                public folly::EventReadCallback,
                public DelayedDestruction {
 public:
  explicit TimerFD(folly::EventBase* eventBase);
  ~TimerFD() override;

  virtual void onTimeout() noexcept = 0;
  void schedule(std::chrono::microseconds timeout);
  void cancel();

  // from folly::EventHandler
  void handlerReady(uint16_t events) noexcept override;

  // from folly::EventReadCallback
  folly::EventReadCallback::IoVec* allocateData() noexcept override {
    auto* ret = ioVecPtr_.release();
    return (ret ? ret : new IoVec(this));
  }

 protected:
  void close();

 private:
  struct IoVec : public folly::EventReadCallback::IoVec {
    IoVec() = delete;
    ~IoVec() override = default;
    explicit IoVec(TimerFD* eventFd) {
      arg_ = eventFd;
      freeFunc_ = IoVec::free;
      cbFunc_ = IoVec::cb;
      data_.iov_base = &timerData_;
      data_.iov_len = sizeof(timerData_);
    }

    static void free(EventReadCallback::IoVec* ioVec) { delete ioVec; }

    static void cb(EventReadCallback::IoVec* ioVec, int res) {
      reinterpret_cast<TimerFD*>(ioVec->arg_)
          ->eventReadCallback(reinterpret_cast<IoVec*>(ioVec), res);
    }

    uint64_t timerData_{0};
  };

  void eventReadCallback(IoVec* ioVec, int res);
  std::unique_ptr<IoVec> ioVecPtr_;

  TimerFD(folly::EventBase* eventBase, int fd);
  static int createTimerFd();

  // use 0 to stop the timer
  bool setTimer(std::chrono::microseconds useconds);

  int fd_{-1};
};
#else
// alternative implementation using a folly::AsyncTimeout
class TimerFD { … };
#endif
} // namespace folly