We have a (very) Legacy application written in VB6 (15 years old?).
The application contains a timer with 300ms interval. The Sub called when the timer ticks executes a batch of code that talks to some SQL servers, prints some labels and so on.
When everything is working OK, this Sub executes in 5ms to 10ms - i.e. before the next timer interval occurs - but it also wastes 290ms before the next tick.
We have a need to make this application a little faster, and one option is to change the interval to 1ms - before we do so, I would just like to confirm whether the timer will abort the interval (aka - completely ignore the tick) if the previous interval is still executing - or will it start building a stack of calls to the sub resulting in a hang after a while? (i am of course assuming all ticks get executed in the same thread as the gui – thus we’ll need to use DoEvents after every tick to ensure the UI doesn’t hang.)
I’ve tried looking into this, but finding reliable information on the old VB6 timers is proving tricky.
We do have this scheduled in to be re-written in .net using threading & background worker threads - this is just a short term fix that we're looking into.
If the timer is a GUI component, (ie. not a thread pool timer), and fired by WM_TIMER 'messages', then the 'OnTimer' events cannot 'stack up'. WM_TIMER is not actually queued to the Windows message queue, it is synthesized when the main thread returns to the message queue AND the timer interval has expired.