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Re: c64/How to predict when garbage collection occurs.. [message #210289 is a reply to message #210288]

Sun, 15 September 2013 05:34

Dombo
Messages: 210
Registered: December 2011

Karma:

Senior Member

Op 15-Sep-13 4:43, Anton Treuenfels schreef:
>
> Anton:
> Do you think you could.. somehow.. come-up with a (Holier than Gawd)
> code snippet, just to see, exactly, how you would approach this scenario??
>
> ---------------------------
>
> Uh, I'm not sure I'd try approaching the problem from the direction of
> an IRQ in any case. I'm not quite sure if you're trying to monitor the
> situation from BASIC via a flag set by an IRQ, or trying to do a
> complete garbage collection within an IRQ handler, or both.
>
> In the first case you'd have to poll the flag from within BASIC,
> presumably using PEEK. If you can do that regularly enough to matter
> then you could also get effectively the same result by PEEKing the
> locations of interest and subtracting their values directly without
> needing to fiddle with an IRQ. As a numerical operation doing so would
> not trigger a garbage collection unless you decided to perform one as a
> result.
>
> In the second case, no matter how much you managed to speed up the
> process it would still be too long for a single interrupt.
>
> In the third case (ha! you didn't know about that one, did you?!) it's
> all moot unless you have a faster garbage collector to use instead of
> the built-in one. Have you?
>
> I did write a replacement once. It worked, but perhaps the only elegant
> thing about it was that I tied it to the FRE() function so it was fairly
> transparent to the system. Other than that it was quite an ugly hack.

Another issue with doing the garbage collection from an IRQ handler is
reentrancy.

I doubt the BASIC interpreter, and the garbage collection routine in
particular, is written with reentrancy in mind. Imagine the BASIC
interpreter loading some pointers to string data, gets interrupted by
the IRQ handler which shuffles the location string data. Once the IRQ
handler has done its thing the BASIC interpreter continues were it was
interrupted, at which point the pointers it loaded before the interrupt
occurred are no longer valid. The effect would be that at seemingly
random times your BASIC program would act weird or locks up the computer.

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[Message index]

		c64/How to predict when garbage collection occurs.. By: Mary Lea Beinhower on Fri, 13 September 2013 20:02
		Re: c64/How to predict when garbage collection occurs.. By: Anton Treuenfels on Fri, 13 September 2013 22:53
		Re: c64/How to predict when garbage collection occurs.. By: Christian Brandt on Sat, 14 September 2013 08:15
		Re: c64/How to predict when garbage collection occurs.. By: epc8 on Tue, 22 October 2013 01:59
		Re: c64/How to predict when garbage collection occurs.. By: Mary Lea Beinhower on Sat, 14 September 2013 15:18
		Re: c64/How to predict when garbage collection occurs.. By: Anton Treuenfels on Sat, 14 September 2013 22:43
		Re: c64/How to predict when garbage collection occurs.. By: Dombo on Sun, 15 September 2013 05:34
		Re: c64/How to predict when garbage collection occurs.. By: Anonymous on Sun, 15 September 2013 06:45
		Re: c64/How to predict when garbage collection occurs.. By: Anton Treuenfels on Mon, 16 September 2013 00:28

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