CMultimediaTimer
CMultimediaTimer
implements a simple periodic timer using the Windows Multimedia Timer API.
N.B.: A Multimedia timer is actually a seperate high priority thread so all the normal multithreading issues apply. As with worker threads, MFC objects should not be called directly from a timer callback due to the Handle Map hoodoo stored in the CWinThread
local storage.
CMultimediaTimer
is not GUI specific as I use it to handle periodic activity in console applications.
To start a timer:
- Derive a loop handler class from
CMultimediaTimerCallback
overiding the OnLoop()
pure virtual
method - Create a
CMultimediaTimer
passing an instance of the derived loop handling class as the constructor parameter - Call the
Start()
method with the loop period in milliseconds as the first parameter.
Usage example:
MyLoopHandlerClass handler;
CMultimediaTimer timer(handler);
timer.Start(20,1);
Classes
CMultimediaTimerCallback
is the callback interface that must be overidden to support loop handling.
We separate loop handling from the main timer
class to prevent calls from within OnLoop()
accidentally calling CMultimediaTimer
methods which could cause a race condition.
class CMultimediaTimerCallback
{
public:
CMultimediaTimerCallback(){}
virtual ~CMultimediaTimerCallback(){}
public:
virtual bool OnLoop()=0;
virtual void OnStarted(){}
virtual void OnStopped(){}
};
CMultimediaTimer
is the timer
class.
To use, simply derive a class from CMultimediaTimer
and override OnLoop()
. Next, call the Start
method with the period in milliseconds as the first parameter.
class CMultimediaTimer
{
public:
CMultimediaTimer(CMultimediaTimerCallback& callback);
virtual ~CMultimediaTimer();
bool Start(UINT nPeriodMs,
MMRESULT& nError,
UINT nResolutionMs = cDefaultTimerResolution);
bool Start(UINT nPeriodMs,UINT nResolutionMs = cDefaultTimerResolution)
{MMRESULT nErr; return Start(nPeriodMs,nErr,nResolutionMs);}
void Stop();
bool Active()const {return m_TimerId != 0;}
UINT GetPeriodMs()const {return m_TimerPeriod;}
UINT GetResolutionMs()const{return m_TimerResolution;}
private:
bool CheckMarker()const;
void ResetPeriodResolution();
void DoLoop();
private:
CMultimediaTimerCallback& m_Callback;
UINT m_TimerPeriod;
UINT m_TimerResolution;
UINT m_TimerId;
bool m_EndTimer;
FLCriticalSection m_StopCriticalSection;
private:
DWORD m_Marker;
friend void CALLBACK mmTimerProc(UINT,UINT,DWORD,DWORD,DWORD);
};
Happy looping!
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