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Topic: Strange crash (Read 913 times) |
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sveinioslo
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Re: Strange crash
« Reply #2 on: Dec 13th, 2012, 1:33pm » |
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> List Variables utility runs in a different, asynchronous, thread it can sometimes pick up data from the heap which is transiently invalid <
So, would this be related to invalid cache or critical section or ...?
This got me started on the assembler, i had been waiting for a reason to dig into the assembler stuff.
More than 20 years since i did anything in assembler.
I was thinking i would like to write a custom LVu with selectable variables + more.
I started to read about critical section (MSDN), but that was a bit too much new info at once.
So i started another 'first x86' project instead.
Been thinking about this issue the past weeks.
If this is a critical section issue:
When i write the custom LVu in assembler:
While running in/from ide, no issues.
While running in/from ide in a PROC and started from timerlib, no issues, timerlib takes care of critical section.
While running in/from ide and called directly from a modified timerlib, take care, if/when error in code, no way of stopping it ??
While running as a separat .exe ??
There were some info about how to enter critical section from an external process.
But i guess it takes some time before i reach that level.
If it's not critical section issue, then ??.
Hope you have time for some info regarding this, i'll do my best to google the things i don't understand.
Svein
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admin
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Re: Strange crash
« Reply #3 on: Dec 13th, 2012, 9:28pm » |
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on Dec 13th, 2012, 1:33pm, sveinioslo wrote:| So, would this be related to invalid cache or critical section or ...? |
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Neither really: it's because a string is represented by a 6-byte descriptor (a 4-byte pointer plus a 2-byte length) and there are no CPU instructions which perform 'atomic' operations on 6-byte blocks. Therefore any communication of a BBC BASIC string between one thread and another will inevitably involve two operations, and there's therefore a possibility that they won't be 'coherent' (in other words the 4-byte address and the 2-byte length won't belong to the same string).
Quote:| I was thinking i would like to write a custom LVu with selectable variables + more. |
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There is already a 'custom' List Variables utility by Malcolm Marten ('List Variables Alternative'), described at the bottom of this Wiki page; I don't know whether that might be a better starting point:
http://bb4w.wikispaces.com/Tools+and+Utilities
Quote:| I started to read about critical section (MSDN), but that was a bit too much new info at once. |
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A Critical Section would certainly be one solution, but that requires both ends to cooperate, and of course you have no way of modifying the BB4W interpreter to use a Critical Section 'at its end'. Indeed such a modification wouldn't be sensible, since it would impair the performance of the interpreter - which is a price too high to pay to fix a minor problem with a debugging tool.
Naturally I'll fix the List Variables crash if and when I release another version of BB4W, but I've no idea when that might be.
Richard.
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sveinioslo
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Re: Strange crash
« Reply #4 on: Dec 14th, 2012, 12:25am » |
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> 6-byte descriptor (a 4-byte pointer plus a 2-byte length) and there are no CPU instructions which perform 'atomic' operations on 6-byte blocks <
Aah!, didn't think of that, very theoretical, yes.
> Naturally I'll fix the List Variables crash if and when <
I'm probably the only one running tests like that.
Now that i know, i'm fine with it as it is.
> List Variables utility by Malcolm Marten <
Haven't tried it, but from the description, it is very far from what i have in mind. It is something i have wanted to do, but not without assembler.
I could upload the running demo skeleton gui design idea, if you are curious.
Svein
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