How to Use Timers in Windows

Question

What are the various ways that a timer can be set up using the Windows API. What are the pros and cons of each method?

I'm using MS DevStudio's C++.

Answer 1

Usually, look at the API you are going to use, for example MFC, Qt or GTK; they all have timer classes.

If you're not going to use a GUI API, I personally like boost::timer (www.boost.org)

Answer 2

There are two timer related functions on the Windows system: SetTimer and KillTimer (I know, the names are odd - CreateTimer and DestroyTimer would be more sensible, as in CreateWindow and DestroyWindow, but that is what is available).

SetTimer can function in one of two modes: the timer event can trigger a user defined callback or it can post a message to a window. The format of this function is:

timer_id = SetTimer (window, event_id, interval, callback);

To use a callback:

timer_id = SetTimer (NULL, NULL, interval_in_milliseconds, callback);

To get a WM_TIMER message to a window:

timer_id = SetTimer (window, event_id, interval_in_milliseconds, NULL);

In both cases, the calling thread needs to have a message queue as both variants issue a WM_TIMER message, the default handler calls the callback function.

Depending on the OS you're using the value of interval has upper and lower bounds. See the API documentation for more details.

To release the timer after you're finished with it do the following if you provided a window handle:

KillTimer (window, event_id); // event_id is important!

and if you used a callback:

KillTimer (NULL, timer_id);

A single window can have many timers associated with it, use a different event_id for each timer. Reusing an event_id stops the first instance of the timer without posting the WM_TIMER message.

Pros: fairly easy to use. Cons: latency between interval end and processing of WM_TIMER message, resolution is large, requires a message processing loop.

Answer 3

Another method for handling timers is to use waitable timer objects. These don't require any message processing, don't use WM_TIMER or callbacks. As such, they're a bit more complex. Understanding the Windows event system will be helpful.

There are three types of timer objects: manual-reset, synchronisation and periodic; and there are four functions for handling the timer objects: CreateWaitableTimer, SetWaitableTimer, CancelWaitableTimer and CloseHandle (there is a fifth, OpenWaitableTimer but that is unlikely to useful to many people). There are also a set of functions required for notification of when a timer expires: WaitForSingleObject, MsgWaitForSingleObject, WaitForMultipleObjects and MsgWaitForMultipleObjects being the most useful.

The usual method for using these timers is:

CreateWaitableTimer (...)
SetWaitableTimer (...)
WaitForSingleObject (...)
CloseHandle (...)

Compare this to SetTimer - the only way to know if a timer has expired is to poll it, either in a loop or with an infinte timeout (i.e. suspend the thread until the timer elapses).

Pros: very flexible, no need to have a message queue. Cons: hard to use

Answer 4

For high resolution timers, use queryperformancecounter