"Critical" API in a DOS window

[Mark Hunter]

I've read about the API call CriticalSection, that
you can use to stop Windows from task switching as
follows:

'code start
! MOV AX,&H1681 'CriticalSection API call
! INT &H2F

'code ..........

'code finish:
! MOV AX,&H1682 'release the Critical Task Block
! INT &H2F

I've also read that this call can be used only for
short periods of time.

I've written an animation program that displays movies
smoothly in pure DOS mode. It uses a millisecond timer.
In a DOS window, I can detect a slight random hesitation
in the movie. I'd like to use the Critical API call to
make the movie smooth in a DOS window.

Questions:

1. How long is it safe to use this Critical API call?
That is, the maximum time between &H1681 and &H1682 ?

2. After using it for that time, how long must you
wait until you can use it again?

I'd like to make the call at program start, then release
it at program finish -- which might be an hour later.

Failing that, I'd like to call and release it repeatedly
and very rapidly.

Mark

[Lance Edmonds]

I use this technique with PBFax for minutes at a time quite successfully. However, it must be noted that it does not "completely disable" Windows - it just switches most of it off. The longest I've let this run is about 5 minutes.

There are no apparent restrictions on duration and frequency of use, but since the PC may need to do other tasks, I would not want this type of code to run on a Server!

As for running it for an hour or more?! Please let us know if you have any problems!

------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Tom Hanlin]

CriticalSection is intended for use with small sections of code that perform
tasks that must not be interrupted in process-- say, updating a jump table
or interrupt vector. Ideally, a critical section should be employed for very
small blocks of code. You wouldn't normally employ a critical block for even
a significant fraction of a second. I would be very hesitant to use it for
longer periods without having a much better understanding of how it is
implemented than I do.

There is not likely to be any point to going in and out of critical sections
in your application. Any processes that have been starved for time will end
up taking their due when you exit the critical section.

It seems that Lance has had some success with using critical sections over
prolonged periods, so you may find it practical to use one over the course
of your entire program's execution. Be advised that this is taking the
intended use of the function way beyond its design, though, so there may be
unwanted side-effects.


------------------
Tom Hanlin
PowerBASIC Staff

[Mark Hunter]

[withdrawn]

[This message has been edited by Mark Hunter (edited April 28, 2006).]