muduo网络库学习笔记(三)TimerQueue定时器队列

muduo网络库学习笔记(三)TimerQueue定时器队列

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TimerQueue是EventLoop的组件之一，可以提供定时任务，和周期任务。

本章首先会简述关于timerfd系统定时函数的基本使用，和TimerQueue类的封装结构,最后给出TimerQueue::addTimer()接口的时序图与使用例子.

Linux中的时间函数

·time(2) / time_t（秒）
·ftime(3) / struct timeb（毫秒）
·gettimeofday(2) / struct timeval（微秒）
·clock_gettime(2) / struct timespec（纳秒）
还有gmtime / localtime / timegm / mktime / strftime / struct tm等与当
前时间无关的时间格式转换函数。
定时函数， 用于让程序等待一段时间或安排计划任务：·sleep(3)
·alarm(2)
·usleep(3)
·nanosleep(2)
·clock_nanosleep(2)
·getitimer(2) / setitimer(2)
·timer_create(2) / timer_settime(2) / timer_gettime(2) / timer_delete(2)
·timerfd_create(2) / timerfd_gettime(2) / timerfd_settime(2)

muduo中做的取舍如下
·（计时） 只使用gettimeofday(2)来获取当前时间。
·（定时） 只使用timerfd_*系列函数来处理定时任务。

gettimeofday(2)入选原因（这也是muduo::Timestamp class的主要设计考虑） ：
1． time(2)的精度太低， ftime(3)已被废弃； clock_gettime(2)精度最高， 但是其系统调用的开销比gettimeofday(2)大。
2． 在x86-64平台上， gettimeofday(2)不是系统调用， 而是在用户态实现的， 没有上下文切换和陷入内核的开销32。
3． gettimeofday(2)的分辨率（resolution） 是1微秒， 现在的实现确实能达到这个计时精度， 足以满足日常计时的需要。 muduo::Timestamp用一个int64_t来表示从Unix Epoch到现在的微秒数， 其范围可达上下30万年。

timerfd_*入选的原因：
1． sleep(3) / alarm(2) / usleep(3)在实现时有可能用了SIGALRM信号， 在多线程程序中处理信号是个相当麻烦的事情， 应当尽量避免， 再说， 如果主程序和程序库都使用SIGALRM， 就糟糕了。
2． nanosleep(2)和clock_nanosleep(2)是线程安全的， 但是在非阻塞网络编程中， 绝对不能用让线程挂起的方式来等待一段时间， 这样一来程序会失去响应。 正确的做法是注册一个时间回调函数。
3． getitimer(2)和timer_create(2)也是用信号来deliver超时，在多线程程序中也会有麻烦。timer_create(2)可以指定信号的接收方是进程还是线程， 算是一个进步， 不过信号处理函数（signal handler） 能做的事情实在很受限。
4．timerfd_create(2)把时间变成了一个文件描述符， 该“文件”在定时器超时的那一刻变得可读， 这样就能很方便地融入select(2)/poll(2)框架中， 用统一的方式来处理IO事件和超时事件， 这也正是Reactor模式的长处。
5． 传统的Reactor利用select(2)/poll(2)/epoll(4)的timeout来实现定时功能， 但poll(2)和epoll_wait(2)的定时精度只有毫秒，远低于timerfd_settime(2)的定时精度。

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timerfd简单使用介绍

本章使用到的两个系统函数:

#include 
int timerfd_create(int clockid, int flags);
int timerfd_settime(int fd, int flags, const struct itimerspec *new_value,struct itimerspec *old_value);

1、timerfd_create函数生成一个定时器,返回与之关联的文件描述,其中的clockid可以设成CLOCK_REALTIME和CLOCK_MONOTONIC
CLOCK_REALTIME:系统实时时间,随系统实时时间改变而改变,即从UTC1970-1-1 0:0:0开始计时,中间时刻如果系统时间被用户改成其他,则对应的时间相应改变
CLOCK_MONOTONIC:从系统启动这一刻起开始计时,不受系统时间被用户改变的影响

2、timerfd_settime用于启停定时器,new_value为超时时间,old_value为周期性定时时间，为0表示不进行周期性定时.

 struct timespec {
      time_t tv_sec;                /* Seconds */
      long   tv_nsec;               /* Nanoseconds */
  };

  struct itimerspec {
     struct timespec it_interval;  /* Interval for periodic timer */
     struct timespec it_value;     /* Initial expiration */
  };

timerfd示例

通过select 监听timerfd，可读时表明到达定时时间.

#include 
#include 
/* According to earlier standards */
#include 
#include 
#include 


int main()
{

  int timerfd = ::timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK |TFD_CLOEXEC);

  struct itimerspec howlong;
  bzero(&howlong, sizeof howlong);
  howlong.it_value.tv_sec = 3;
  timerfd_settime(timerfd, 0, &howlong, NULL);

  fd_set rdset;
  FD_ZERO(&rdset);
  FD_SET(timerfd, &rdset);

  struct timeval timeout;
  timeout.tv_sec = 1;
  timeout.tv_usec = 0;
  while(1)
  {
    if(select(timerfd + 1, &rdset, NULL, NULL, &timeout) == 0)
    {
      std::cout << "timeout\n";
      timeout.tv_sec = 1;
      timeout.tv_usec = 0;
      FD_SET(timerfd, &rdset);
        continue;
    }
    std::cout << " timer happend\n";
    break;
  }


  close(timerfd);

  return 0;
}

/* print
timeout
timeout
timer happend
*/

muduo中对timerfd的封装

int createTimerfd()
{
  int timerfd = ::timerfd_create(CLOCK_MONOTONIC,
                                 TFD_NONBLOCK | TFD_CLOEXEC);
  if (timerfd < 0)
  {
    std::cout << "Failed in timerfd_create" << std::endl;
    abort();
  }
  return timerfd;
}

struct timespec howMuchTimeFromNow(TimeStamp when)
{
  int64_t microseconds = when.microSecondsSinceEpoch()
                         - TimeStamp::now().microSecondsSinceEpoch();
  if (microseconds < 100)
  {
    microseconds = 100;
  }
  struct timespec ts;
  ts.tv_sec = static_cast(
      microseconds / TimeStamp::kMicroSecondsPerSecond);
  ts.tv_nsec = static_cast(
      (microseconds % TimeStamp::kMicroSecondsPerSecond) * 1000);
  return ts;
}

void readTimerfd(int timerfd, TimeStamp now)
{
  uint64_t howmany;
  ssize_t n = ::read(timerfd, &howmany, sizeof howmany);
  std::cout << "TimerQueue::handleRead() " << howmany << " at " << now.toString() << std::endl;
  if (n != sizeof howmany)
  {
    std::cout << "TimerQueue::handleRead() reads " << n << " bytes instead of 8" << std::endl;
  }
}

void resetTimerfd(int timerfd, TimeStamp expiration)
{
  // wake up loop by timerfd_settime()
  struct itimerspec newValue;
  struct itimerspec oldValue;
  bzero(&newValue, sizeof newValue);
  bzero(&oldValue, sizeof oldValue);
  newValue.it_value = howMuchTimeFromNow(expiration);
  int ret = ::timerfd_settime(timerfd, 0, &newValue, &oldValue);
  if (ret)
  {
    std::cout << "timerfd_settime()" << std::endl;
  }
}

TimerQueue的结构.

TimerQueue只提供了两个对外的接口
addTimer() 添加一个定时器超时执行回调函数cb. interval是周期性定时时间，本章不讲,置零不打开.
cancel() 取消一个定时器,本章也不细述,本章只介绍addTimer()接口.后面如果需要会补充本章.

TimerQueue定义如下

class TimerQueue
{
public:
  TimerQueue(EventLoop* loop);
  ~TimerQueue();

  // Schedules the callback to be run at given time,

  TimerId addTimer(const NetCallBacks::TimerCallBack& cb, TimeStamp when, double interval = 0.0);

  void cancel(TimerId timerId);

private:
  /*
    .....
  */
  EventLoop* p_loop;
  const int m_timerfd;
  Channel m_timerfdChannel;

  //Timer List sorted by expiration
  TimerList m_timers;
  ActiveTimerSet m_activeTimers;
};

虽然只提供了两个对外接口，但是私有成比较复杂,首先简介成员Timer.

Timer

Timer类作为TimerQueue的内部成员使用,封装一个定时器,addTimer()接口调用后生成一个Timer()，外头的回调函数和定时反应时间会封装再此Timer中.
Tiemr主要接口都是获取这些构造时配置的成员值
run() 调用回调函数.
expiration 定时器过期时间.
interval 周期性定时时间.
repeat 是否是周期性定时.
sequence 一个静态成员,用于记录Timer创建的个数. 为了保证它的线程安全性，使用AtomicInt64封装了一层原子操作.

TimerId 用于Cancel Timer的标志Id, 这两个类都不复杂，可自行参看muduo源码，也可翻我github上的SimpleMuduo单独类文件夹下的测试代码.

  Timer(const NetCallBacks::TimerCallBack& cb, TimeStamp when, double interval)
  :m_callBack(cb),
  m_expiration(when),
  m_interval(interval),
  m_repeat(interval > 0.0),
  m_sequence(s_numCreated.incrementAndGet())

TimerId TimerQueue::addTimer(const NetCallBacks::TimerCallBack& cb, TimeStamp when, double interval)
{
  Timer* timer = new Timer(cb, when, interval);
  //p_loop->runInLoop(std::bind(&TimerQueue::addTimerInLoop, this, timer));
  return TimerId(timer, timer->sequence());
}

Timer的容器.

  typedef std::pair Entry;
  typedef std::set TimerList;
  typedef std::pair ActiveTimer;
  typedef std::set ActiveTimerSet;

为了解决无法处理两个Timer到期时间相同的情况。使用了pair将时间戳和Timer的地址组成了一对.然后使用Set存储.
ActiveTimer 将Timer和sequence组成一对主要作用来索引迭代的.

TimerQueue私有接口介绍.

  void addTimerInLoop(Timer* timer);
  void cancelInLoop(TimerId timerId);
  //called when timerfd alarms
  void handleRead();
  //move out all expired timers and return they.
  std::vector getExpired(TimeStamp now);
  bool insert(Timer* timer);
  void reset(const std::vector& expired, TimeStamp now);

添加定时器

bool insert(Timer* timer); //插入一个定时器.

EventLoop添加了一个runInLoop接口： 在它的IO线程内执行某个用户
任务回调， 即EventLoop::runInLoop(const Functor& cb)， 其中Functor是
std::function。 如果用户在当前IO线程调用这个函数， 回调会
同步进行； 如果用户在其他线程调用runInLoop()， cb会被加入队列， IO
线程会被唤醒来调用这个Functor。

addTimer()使用了EventLoop的runInLoop接口(这个接口主要来保证线程安全性的，暂不讲)，来执行addTimerInLoop().addTimerInLoop()调用insert()插入定时器.
如果此定时器是最早触发的那一个则会调用resetTimerfd()->timerfd_settime()启动定时器.

addTimer()->addTimerInLoop()->insert()->resetTimerfd()->timerfd_settime()

更新定时器

添加逻辑就在上面了，下面给出处理逻辑.
三个接口.
void handleRead(); //定时器触发回调.获取已过期的事件并处理随后更新列表.
std::vector getExpired(TimeStamp now);//获取一组已过期的定时器,并从TimerList中删除.
void reset(const std::vector & expired, TimeStamp now);//如果是周期性任务则重新配置时间插入，随后调用resetTimerfd()更新下一定时任务.

handleRead()->getExpired()->Timer->run(cb)->reset()->resetTimerfd()->timerfd_settime()

时序图

TimerQueue源码

#ifndef _NET_TIMERQUEUE_HH
#define _NET_TIMERQUEUE_HH
#include "TimerId.hh"
#include "CallBacks.hh"
#include "TimeStamp.hh"
#include "Channel.hh"
#include 
#include 

class EventLoop;

class TimerQueue
{
public:
  TimerQueue(EventLoop* loop);
  ~TimerQueue();

  // Schedules the callback to be run at given time,

  TimerId addTimer(const NetCallBacks::TimerCallBack& cb, TimeStamp when, double interval = 0.0);

  void cancel(TimerId timerId);

private:
  typedef std::pair Entry;
  typedef std::set TimerList;
  typedef std::pair ActiveTimer;
  typedef std::set ActiveTimerSet;

  void addTimerInLoop(Timer* timer);
  void cancelInLoop(TimerId timerId);
  //called when timerfd alarms
  void handleRead();
  //move out all expired timers and return they.
  std::vector getExpired(TimeStamp now);
  bool insert(Timer* timer);
  void reset(const std::vector& expired, TimeStamp now);

  EventLoop* p_loop;
  const int m_timerfd;
  Channel m_timerfdChannel;

  //Timer List sorted by expiration
  TimerList m_timers;
  ActiveTimerSet m_activeTimers;

  bool m_callingExpiredTimers; /*atomic*/
  ActiveTimerSet m_cancelingTimers;

};

#endif

//TimerQueeu.cpp

#include 
#include 
#include 
#include 

#include "Logger.hh"
#include "EventLoop.hh"
#include "Timer.hh"
#include "TimerQueue.hh"

namespace TimerFd
{

int createTimerfd()
{
  int timerfd = ::timerfd_create(CLOCK_MONOTONIC,
                                 TFD_NONBLOCK | TFD_CLOEXEC);
  if (timerfd < 0)
  {
    LOG_SYSFATAL << "Failed in timerfd_create";
  }
  return timerfd;
}

struct timespec howMuchTimeFromNow(TimeStamp when)
{
  int64_t microseconds = when.microSecondsSinceEpoch()
                         - TimeStamp::now().microSecondsSinceEpoch();
  if (microseconds < 100)
  {
    microseconds = 100;
  }
  struct timespec ts;
  ts.tv_sec = static_cast(
      microseconds / TimeStamp::kMicroSecondsPerSecond);
  ts.tv_nsec = static_cast(
      (microseconds % TimeStamp::kMicroSecondsPerSecond) * 1000);
  return ts;
}

void readTimerfd(int timerfd, TimeStamp now)
{
  uint64_t howmany;
  ssize_t n = ::read(timerfd, &howmany, sizeof howmany);
  LOG_TRACE << "TimerQueue::handleRead() " << howmany << " at " << now.toString();
  if (n != sizeof howmany)
  {
    LOG_ERROR << "TimerQueue::handleRead() reads " << n << " bytes instead of 8";
  }
}

void resetTimerfd(int timerfd, TimeStamp expiration)
{
  // wake up loop by timerfd_settime()
  LOG_TRACE << "resetTimerfd()";
  struct itimerspec newValue;
  struct itimerspec oldValue;
  bzero(&newValue, sizeof newValue);
  bzero(&oldValue, sizeof oldValue);
  newValue.it_value = howMuchTimeFromNow(expiration);
  int ret = ::timerfd_settime(timerfd, 0, &newValue, &oldValue);
  if (ret)
  {
    LOG_SYSERR << "timerfd_settime()";
  }
}

};

using namespace TimerFd;

TimerQueue::TimerQueue(EventLoop* loop)
  :p_loop(loop),
   m_timerfd(createTimerfd()),
   m_timerfdChannel(p_loop, m_timerfd),
   m_timers(),
   m_callingExpiredTimers(false)
{
  m_timerfdChannel.setReadCallBack(std::bind(&TimerQueue::handleRead, this));
  m_timerfdChannel.enableReading();
}

TimerQueue::~TimerQueue()
{
  m_timerfdChannel.disableAll();
  m_timerfdChannel.remove();
  ::close(m_timerfd);
  for (TimerList::iterator it = m_timers.begin();
      it != m_timers.end(); ++it)
  {
    delete it->second;
  }
}

std::vector TimerQueue::getExpired(TimeStamp now)
{
  std::vector expired;
  Entry sentry = std::make_pair(now, reinterpret_castUINTPTR_MAX);
  TimerList::iterator it = m_timers.lower_bound(sentry);
  assert(it == m_timers.end() || now < it->first);
  std::copy(m_timers.begin(), it, back_inserter(expired));
  m_timers.erase(m_timers.begin(), it);

  for(std::vector::iterator it = expired.begin();
      it != expired.end(); ++it)
  {
    ActiveTimer timer(it->second, it->second->sequence());
    size_t n = m_activeTimers.erase(timer);
    assert(n == 1); (void)n;
  }

  assert(m_timers.size() == m_activeTimers.size());

  return expired;
}


TimerId TimerQueue::addTimer(const NetCallBacks::TimerCallBack& cb, TimeStamp when, double interval)
{
  Timer* timer = new Timer(cb, when, interval);
  p_loop->runInLoop(std::bind(&TimerQueue::addTimerInLoop, this, timer));
  return TimerId(timer, timer->sequence());
}

void TimerQueue::addTimerInLoop(Timer* timer)
{
  p_loop->assertInLoopThread();
  bool earliestChanged = insert(timer);

  if (earliestChanged)
  {
    resetTimerfd(m_timerfd, timer->expiration());
  }
}

void TimerQueue::cancel(TimerId timerId)
{
  p_loop->runInLoop(std::bind(&TimerQueue::cancelInLoop, this, timerId));
}

void TimerQueue::cancelInLoop(TimerId timerId)
{
  p_loop->assertInLoopThread();
  assert(m_timers.size() ==  m_activeTimers.size());
  ActiveTimer timer(timerId.m_timer, timerId.m_sequence);
  ActiveTimerSet::iterator it = m_activeTimers.find(timer);
  if(it != m_activeTimers.end())
  {
    size_t n = m_timers.erase(Entry(it->first->expiration(), it->first));
    assert(n == 1);
    delete it->first;
  }
  else if (m_callingExpiredTimers)
  {
    m_cancelingTimers.insert(timer);
  }
  assert(m_timers.size() == m_activeTimers.size());
}

bool TimerQueue::insert(Timer* timer)
{
  p_loop->assertInLoopThread();
  assert(m_timers.size() == m_activeTimers.size());
  bool earliestChanged = false;
  TimeStamp when = timer->expiration();
  TimerList::iterator it = m_timers.begin();
  if (it == m_timers.end() || when < it->first)
  {
    earliestChanged = true;
  }
  {
    std::pair result
      = m_timers.insert(Entry(when, timer));
    assert(result.second); (void)result;
  }
  {
    std::pair result
      = m_activeTimers.insert(ActiveTimer(timer, timer->sequence()));
    assert(result.second); (void)result;
  }

  LOG_TRACE << "TimerQueue::insert() " << "m_timers.size() : "
  << m_timers.size() << " m_activeTimers.size() : " << m_activeTimers.size();

  assert(m_timers.size() == m_activeTimers.size());
  return earliestChanged;
}


void TimerQueue::handleRead()
{
  p_loop->assertInLoopThread();
  TimeStamp now(TimeStamp::now());
  readTimerfd(m_timerfd, now);

  std::vector expired = getExpired(now);

  LOG_TRACE << "Expired Timer size " << expired.size() << "  ";

  m_callingExpiredTimers = true;
  m_cancelingTimers.clear();

  for(std::vector::iterator it = expired.begin();
      it != expired.end(); ++it )
  {
    it->second->run();
  }

  m_callingExpiredTimers = false;

  reset(expired, now);
}


void TimerQueue::reset(const std::vector& expired, TimeStamp now)
{
  TimeStamp nextExpire;

  for(std::vector::const_iterator it = expired.begin();
      it != expired.end(); ++it)
  {
    ActiveTimer timer(it->second, it->second->sequence());
    if(it->second->repeat()
      && m_cancelingTimers.find(timer) == m_cancelingTimers.end())
    {//如果是周期定时器则重新设定时间插入. 否则delete.
      it->second->restart(now);
      insert(it->second);
    }
    else
    {// FIXME move to a free list no delete please
      delete it->second;
    }
  }

  if (!m_timers.empty())
  {
    nextExpire = m_timers.begin()->second->expiration();
  }

  if (nextExpire.valid())
  {
    resetTimerfd(m_timerfd, nextExpire);
  }
}

TimerQueue使用示例

测试TimerQueue的addTimer接口.

#include 
#include 
#include 
#include 
#include 
#include "EventLoop.hh"
#include "Channel.hh"
#include "Poller.hh"
#include "Logger.hh"
#include "Timer.hh"
#include "TimeStamp.hh"
#include "TimerQueue.hh"

EventLoop* g_loop;

void print() { LOG_DEBUG << "test print()";  }

void test()
{

  LOG_DEBUG << "[test] : test timerQue";

}


int main()
{
  EventLoop loop;
  g_loop = &loop;

  TimerQueue timerQue(&loop);
  timerQue.addTimer(test, times::addTime(TimeStamp::now(), 3.0));
  timerQue.addTimer(test, times::addTime(TimeStamp::now(), 3.0));
  timerQue.addTimer(test, times::addTime(TimeStamp::now(), 5.0));

  loop.loop();

  return 0;
}

./test.out 
2018-11-11 15:49:22.493990 [TRACE] [Poller.cpp:64] [updateChannel] fd= 3 events3
2018-11-11 15:49:22.494042 [TRACE] [EventLoop.cpp:34] [EventLoop] EventLoop Create 0x7FFFBD3C39B0 in thread 3262
2018-11-11 15:49:22.494047 [TRACE] [Poller.cpp:64] [updateChannel] fd= 5 events3
2018-11-11 15:49:22.494055 [TRACE] [TimerQueue.cpp:172] [insert] TimerQueue::insert() m_timers.size() : 1 m_activeTimers.size() : 1
2018-11-11 15:49:22.494058 [TRACE] [TimerQueue.cpp:55] [resetTimerfd] resetTimerfd()
2018-11-11 15:49:22.494066 [TRACE] [TimerQueue.cpp:172] [insert] TimerQueue::insert() m_timers.size() : 2 m_activeTimers.size() : 2
2018-11-11 15:49:22.494070 [TRACE] [TimerQueue.cpp:172] [insert] TimerQueue::insert() m_timers.size() : 3 m_activeTimers.size() : 3
2018-11-11 15:49:22.494073 [TRACE] [EventLoop.cpp:59] [loop] EventLoop 0x7FFFBD3C39B0 start loopig
2018-11-11 15:49:22.494075 [TRACE] [Poller.cpp:20] [poll] Poller::poll()
2018-11-11 15:49:23.495462 [TRACE] [Poller.cpp:28] [poll]  nothing happended
2018-11-11 15:49:23.495488 [TRACE] [Poller.cpp:20] [poll] Poller::poll()
2018-11-11 15:49:24.496618 [TRACE] [Poller.cpp:28] [poll]  nothing happended
2018-11-11 15:49:24.496640 [TRACE] [Poller.cpp:20] [poll] Poller::poll()
2018-11-11 15:49:25.494222 [TRACE] [Poller.cpp:24] [poll] 1 events happended
2018-11-11 15:49:25.494253 [TRACE] [TimerQueue.cpp:45] [readTimerfd] TimerQueue::handleRead() 1 at 1541922565.494251
2018-11-11 15:49:25.494316 [TRACE] [TimerQueue.cpp:188] [handleRead] Expired Timer size 2  

2018-11-11 15:49:25.494320 [DEBUG] [main.cpp:50] [test] [test] : test timerQue
2018-11-11 15:49:25.494322 [DEBUG] [main.cpp:50] [test] [test] : test timerQue

2018-11-11 15:49:25.494325 [TRACE] [TimerQueue.cpp:55] [resetTimerfd] resetTimerfd()
2018-11-11 15:49:25.494332 [TRACE] [Poller.cpp:20] [poll] Poller::poll()
2018-11-11 15:49:26.496293 [TRACE] [Poller.cpp:28] [poll]  nothing happended
2018-11-11 15:49:26.496318 [TRACE] [Poller.cpp:20] [poll] Poller::poll()
2018-11-11 15:49:27.494291 [TRACE] [Poller.cpp:24] [poll] 1 events happended
2018-11-11 15:49:27.494319 [TRACE] [TimerQueue.cpp:45] [readTimerfd] TimerQueue::handleRead() 1 at 1541922567.494317
2018-11-11 15:49:27.494328 [TRACE] [TimerQueue.cpp:188] [handleRead] Expired Timer size 1  

2018-11-11 15:49:27.494331 [DEBUG] [main.cpp:50] [test] [test] : test timerQue

2018-11-11 15:49:27.494334 [TRACE] [Poller.cpp:20] [poll] Poller::poll()
2018-11-11 15:49:28.495665 [TRACE] [Poller.cpp:28] [poll]  nothing happended