muduo網路庫學習筆記(三)TimerQueue定時器佇列
阿新 • • 發佈：2018-11-11
目錄
muduo網路庫學習筆記(三)TimerQueue定時器佇列
本章整理muduo中的TimerQueue，會簡述關於timerfd系統定時函式的基本使用，和TimerQueue類的封裝結構,最後給出TimerQueue::addTimer()介面的時序圖.
Linux中的時間函式
·time(2) / time_t（秒）
·ftime(3) / struct timeb（毫秒）
·gettimeofday(2) / struct timeval（微秒）
·clock_gettime(2) / struct timespec（納秒）
還有gmtime / localtime / timegm / mktime / strftime / struct tm等與當
前時間無關的時間格式轉換函式。
定時函式， 用於讓程式等待一段時間或安排計劃任務：·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中做的取捨如下
·（計時） 只使用gettimeofday(2)來獲取當前時間。
·（定時） 只使用timerfd_*系列函式來處理定時任務。
gettimeofday(2)入選原因（這也是muduo::Timestamp class的主要設計考慮） ：
1． time(2)的精度太低， ftime(3)已被廢棄； clock_gettime(2)精度最高， 但是其系統呼叫的開銷比gettimeofday(2)大。
2． 在x86-64平臺上， gettimeofday(2)不是系統呼叫， 而是在使用者態實現的， 沒有上下文切換和陷入核心的開銷32。
3． gettimeofday(2)的解析度（resolution） 是1微秒， 現在的實現確實能達到這個計時精度， 足以滿足日常計時的需要。 muduo::Timestamp用一個int64_t來表示從Unix Epoch到現在的微秒數， 其範圍可達上下30萬年。
timerfd_*入選的原因：
1． sleep(3) / alarm(2) / usleep(3)在實現時有可能用了SIGALRM訊號， 在多執行緒程式中處理訊號是個相當麻煩的事情， 應當儘量避免， 再說， 如果主程式和程式庫都使用SIGALRM， 就糟糕了。
2． nanosleep(2)和clock_nanosleep(2)是執行緒安全的， 但是在非阻塞網路程式設計中， 絕對不能用讓執行緒掛起的方式來等待一段時間， 這樣一來程式會失去響應。 正確的做法是註冊一個時間回撥函式。
3． getitimer(2)和timer_create(2)也是用訊號來deliver超時，在多執行緒程式中也會有麻煩。timer_create(2)可以指定訊號的接收方是程序還是執行緒， 算是一個進步， 不過訊號處理函式（signal handler） 能做的事情實在很受限。
4．timerfd_create(2)把時間變成了一個檔案描述符， 該“檔案”在定時器超時的那一刻變得可讀， 這樣就能很方便地融入select(2)/poll(2)框架中， 用統一的方式來處理IO事件和超時事件， 這也正是Reactor模式的長處。
5． 傳統的Reactor利用select(2)/poll(2)/epoll(4)的timeout來實現定時功能， 但poll(2)和epoll_wait(2)的定時精度只有毫秒，遠低於timerfd_settime(2)的定時精度。
timerfd簡單使用介紹
本章使用到的兩個系統函式:
#include <sys/timerfd.h>
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函式生成一個定時器,返回與之關聯的檔案描述,其中的clockid可以設成CLOCK_REALTIME和CLOCK_MONOTONIC
CLOCK_REALTIME:系統實時時間,隨系統實時時間改變而改變,即從UTC1970-1-1 0:0:0開始計時,中間時刻如果系統時間被使用者改成其他,則對應的時間相應改變
CLOCK_MONOTONIC:從系統啟動這一刻起開始計時,不受系統時間被使用者改變的影響
2、timerfd_settime用於啟停定時器,new_value為超時時間,old_value為週期性定時時間，為0表示不進行週期性定時.
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
通過select 監聽timerfd，可讀時表明到達定時時間.
#include <sys/timerfd.h>
#include <sys/select.h>
/* According to earlier standards */
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
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中對timerfd的封裝
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<time_t>(
microseconds / TimeStamp::kMicroSecondsPerSecond);
ts.tv_nsec = static_cast<long>(
(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的結構.
TimerQueue只提供了兩個對外的介面
addTimer()新增一個定時器超時執行回撥函式cb. interval是週期性定時時間，本章不講,置零不開啟.
cancel() 取消一個定時器,本章也不細述,本章只介紹addTimer()介面.後面如果需要會補充本章.
TimerQueue定義如下
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;
};雖然只提供了兩個對外介面，但是私有成比較複雜,首先簡介成員Timer.
Timer
Timer類作為TimerQueue的內部成員使用,封裝一個定時器,addTimer()介面呼叫後生成一個Timer()，外頭的回撥函式和定時反應時間會封裝再此Timer中.
Tiemr主要介面都是獲取這些構造時配置的成員值
run() 呼叫回撥函式.
expiration 定時器過期時間.
interval 週期性定時時間.
repeat 是否是週期性定時.
sequence 一個靜態成員,用於記錄Timer建立的個數. 為了保證它的執行緒安全性，使用AtomicInt64封裝了一層原子操作.
TimerId 用於Cancel Timer的標誌Id, 這兩個類都不復雜，可自行參看muduo原始碼，也可翻我github上的SimpleMuduo單獨類資料夾下的測試程式碼.
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<TimeStamp, Timer*> Entry;
typedef std::set<Entry> TimerList;
typedef std::pair<Timer*, int64_t> ActiveTimer;
typedef std::set<ActiveTimer> ActiveTimerSet;為了解決無法處理兩個Timer到期時間相同的情況。使用了pair將時間戳和Timer的地址組成了一對.然後使用Set儲存.
ActiveTimer 將Timer和sequence組成一對主要作用來索引迭代的.
TimerQueue私有介面介紹.
void addTimerInLoop(Timer* timer);
void cancelInLoop(TimerId timerId);
//called when timerfd alarms
void handleRead();
//move out all expired timers and return they.
std::vector<Entry> getExpired(TimeStamp now);
bool insert(Timer* timer);
void reset(const std::vector<Entry>& expired, TimeStamp now);
新增定時器
bool insert(Timer* timer); //插入一個定時器.
EventLoop添加了一個runInLoop介面： 在它的IO執行緒內執行某個使用者
任務回撥， 即EventLoop::runInLoop(const Functor& cb)， 其中Functor是
std::function<void()>。 如果使用者在當前IO執行緒呼叫這個函式， 回撥會
同步進行； 如果使用者在其他執行緒呼叫runInLoop()， cb會被加入佇列， IO
執行緒會被喚醒來呼叫這個Functor。
addTimer()使用了EventLoop的runInLoop介面(這個介面主要來保證執行緒安全性的，暫不講)，來執行addTimerInLoop().addTimerInLoop()呼叫insert()插入定時器.
如果此定時器是最早觸發的那一個則會呼叫resetTimerfd()->timerfd_settime()啟動定時器.
addTimer()->addTimerInLoop()->insert()->resetTimerfd()->timerfd_settime()
更新定時器
新增邏輯就在上面了，下面給出處理邏輯.
三個介面.
void handleRead(); //定時器觸發回撥.獲取已過期的事件並處理隨後更新列表.
std::vector
handleRead()->getExpired()->Timer->run(cb)->reset()->resetTimerfd()->timerfd_settime()
時序圖
TimerQueue原始碼
#ifndef _NET_TIMERQUEUE_HH
#define _NET_TIMERQUEUE_HH
#include "TimerId.hh"
#include "CallBacks.hh"
#include "TimeStamp.hh"
#include "Channel.hh"
#include <set>
#include <vector>
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<TimeStamp, Timer*> Entry;
typedef std::set<Entry> TimerList;
typedef std::pair<Timer*, int64_t> ActiveTimer;
typedef std::set<ActiveTimer> 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<Entry> getExpired(TimeStamp now);
bool insert(Timer* timer);
void reset(const std::vector<Entry>& 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 <stdint.h>
#include <assert.h>
#include <sys/timerfd.h>
#include <unistd.h>
#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<time_t>(
microseconds / TimeStamp::kMicroSecondsPerSecond);
ts.tv_nsec = static_cast<long>(
(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::Entry> TimerQueue::getExpired(TimeStamp now)
{
std::vector<Entry> expired;
Entry sentry = std::make_pair(now, reinterpret_cast<Timer*>UINTPTR_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<Entry>::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<TimerList::iterator, bool> result
= m_timers.insert(Entry(when, timer));
assert(result.second); (void)result;
}
{
std::pair<ActiveTimerSet::iterator, bool> 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<Entry> expired = getExpired(now);
LOG_TRACE << "Expired Timer size " << expired.size() << " ";
m_callingExpiredTimers = true;
m_cancelingTimers.clear();
for(std::vector<Entry>::iterator it = expired.begin();
it != expired.end(); ++it )
{
it->second->run();
}
m_callingExpiredTimers = false;
reset(expired, now);
}
void TimerQueue::reset(const std::vector<Entry>& expired, TimeStamp now)
{
TimeStamp nextExpire;
for(std::vector<Entry>::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())
{//如果是週期定時器則重新設定時間插入. 否則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
測試TimerQueue的addTimer介面.
#include <errno.h>
#include <thread>
#include <strings.h>
#include <poll.h>
#include <functional>
#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