CODEWITHSUNDEEP
visual-c++
Tongkki
Tongkki

Reputation: 13

How to make WM_TIMER msg be called in ordered sequence in WinApi?

I'm doing winapi programming and i usually have a problems related to WM_TIMER msg: for example, when i put function that activates when WM_TIMER msg is called, like Update() function for example, this function is still called even though i killed timer. What's the main problem right now is that when i believe that i deleted the class that contain Update() function, this class still calls Update() function even though i killed timer and this class first, and because of this, i get memory error because this Update() function deals with attributes that are already deleted in previous delete function. Is there any solution to make WM_TIMER be called after certain task is done?

Upvotes: 0

Views: 274

Answers (1)

Simon Richter
Simon Richter

Reputation: 29586

The WM_TIMER message is actually a flag -- when some timer expires, the flag is set to generate a single WM_TIMER event if the message queue is empty and GetMessage is called.

This avoids clogging up the system with many WM_TIMER messages and collapses multiple expired timers into one, but has the disadvantage of delivering the WM_TIMER message after all other messages (WM_PAINT is treated similarly).

So what you are seeing is that the timer you have killed has already elapsed and the flag is set, but the message will not be delivered until your program is otherwise idle.

You want to keep a flag to memorize whether you are actually waiting for a timer event.

In an application with multiple timers in parallel you'd keep a list of active timers, and use the Windows timer mechanism to schedule the next timer to elapse, and in the handler, invoke all sub-handlers whose deadlines are past.

Upvotes: 1

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