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Delphi events and processing

Posted on 2001-06-22
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Last Modified: 2010-04-06
What is the outcome when there are 2 different events calling the same procedure? will the procedure be pre-empted or will delphi create another instance of that procedure?

given:
 * 2 timers - TimerA and TimerB both enabled at the same time with the same time interval
 * 1 common procedure - Procedure Process_Data(code: string); (doing some lengthy processing)
    if code=A then process with parameter A
    if code=B then process with parameter B

sequence of events:
 * enable TimerA and TimerB
 * OnTimer of TimerA - call Process_Data('A');
   OnTimer of TimerB - call Process_Data('B');

how is the procedure going to proceed? will there be time-slicing? and if so, what are the priorities?
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Question by:ttanyag
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Madshi earned 100 total points
ID: 6217588
Windows timers work via messages. That means, as long as you don't handle messages, no timer is fired. That again means, if the first timer is fired, your callback function is called. If you don't do any message handling in this function, the second timer has to wait (even if the time is over), until your callback function is run through. Only then (hopefully someone else now handles messages, e.g. Application.Run does) the second timer is finally fired.

Delphi doesn't copy a procedure "instance" or code. If you create 2 timers that share the same callback function, then the same function is called. However, if you use Delphi's TTimer object (instead of pure win32 API), you can use "Self" to differ between the different parent timers.

Time slicing only applies to threads. Timers are no threads. One after the other is the mode, except if you're handling messages in the timer callback function, then the second timer may be fired, while the first is not fully handled yet. But then the first timer is "paused" as long as the 2nd is not finished.

Regards, Madshi.
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