定时器timer是多线程编程中经常设计到的工具类

定时器的原理其实很简单：

• 创建一个新线程
• 在那个线程里等待
• 等待指定时长后做任务

这里用C++11实现了一个简单易用的定时器，包含两种模式：

• 周期性定时任务执行
• 单次延时任务执行

timer.hpp

#ifndef _TIMER_H_
#define _TIMER_H_

#include <functional>
#include <chrono>
#include <thread>
#include <atomic>
#include <memory>
#include <mutex>
#include <condition_variable>

class Timer
{
public:
 Timer(): _expired(true), _try_to_expire(false)
 {}

 Timer(const Timer& timer)
 {
 _expired = timer._expired.load();
 _try_to_expire = timer._try_to_expire.load();
 }

 ~Timer()
 {
 stop();
 }

 void start(int interval, std::function<void()> task)
 {
 // is started, do not start again
 if (_expired == false)
  return;

 // start async timer, launch thread and wait in that thread
 _expired = false;
 std::thread([this, interval, task]() {
  while (!_try_to_expire)
  {
  // sleep every interval and do the task again and again until times up
  std::this_thread::sleep_for(std::chrono::milliseconds(interval));
  task();
  }

  {
  // timer be stopped, update the condition variable expired and wake main thread
  std::lock_guard<std::mutex> locker(_mutex);
  _expired = true;
  _expired_cond.notify_one();
  }
 }).detach();
 }

 void startOnce(int delay, std::function<void()> task)
 {
 std::thread([delay, task]() {
  std::this_thread::sleep_for(std::chrono::milliseconds(delay));
  task();
 }).detach();
 }

 void stop()
 {
 // do not stop again
 if (_expired)
  return;

 if (_try_to_expire)
  return;

 // wait until timer 
 _try_to_expire = true; // change this bool value to make timer while loop stop
 {
  std::unique_lock<std::mutex> locker(_mutex);
  _expired_cond.wait(locker, [this] {return _expired == true; });

  // reset the timer
  if (_expired == true)
  _try_to_expire = false;
 }
 }

private:
 std::atomic<bool> _expired; // timer stopped status
 std::atomic<bool> _try_to_expire; // timer is in stop process
 std::mutex _mutex;
 std::condition_variable _expired_cond;
};

#endif // !_TIMER_H_

main.cpp

#include <iostream>
#include "timer.hpp"

void func1()
{
 std::cout << "trigger func1" << std::endl;
}

void func2(int x)
{
 std::cout << "trigger func2, x: " << x << std::endl;
}

int main(int argc, char* argv[])
{
 Timer timer;

 // execute task every timer interval
 std::cout << "--- start period timer ----" << std::endl;
 timer.start(1000, std::bind(func2, 3));
 std::this_thread::sleep_for(std::chrono::milliseconds(5000));
 timer.stop();
 std::cout << "--- stop period timer ----" << std::endl;

  // execute task once after delay
 std::cout << "--- start one shot timer ----" << std::endl;
 timer.startOnce(1000, func1);
 std::cout << "--- stop one shot timer ----" << std::endl;

 getchar();
 return 0;
}

运行结果

--- start period timer ----
trigger func2, x: 3
trigger func2, x: 3
trigger func2, x: 3
trigger func2, x: 3
trigger func2, x: 3
--- stop period timer ----
--- start one shot timer ----
--- stop one shot timer ----
trigger func1