Re: [cc65] Re: signals

Jonathan Graham Harston wrote:

>>Message-ID: <4299ACB3.5040203@brahms.demon.co.uk>
>>    
>>
> 
>dominic beesley <dominic@brahms.demon.co.uk> wrote:
>  
>
>>I guess really the main worry is that I'm in the middle of
>>updating one of the file structures. I'm trying to work out if an
>>Escape is ever delivered in the middle of an OS operation. In
>>    
>>
> 
>Yes, Escapes can happen at *any* time when IRQs are enabled. The
>foreground program should check for an escape state at safe points
>in the program, eg between BASIC statements, at the end or start
>of loops, after a received keypress.
>  
>
>>which case it gets very messy. Otherwise I'll just try and make
>>sure that the cleanup code uses some kind of semaphore to protect
>>other file ops (and possibly delays the Escape handling until
>>after it has happened).
>>    
>>
> 
>Don't abort on Escape! It's so much easier. Just let Escape set
>its flag in the background. Let the foreground check for it.
> 
>It's no good saying you'll close all open files (or files opened
>by the program) on an escape-induced abort. What if you abort
>halfway through a file delete? The directory may have been written
>to disk before the free space map has been written. Even worse,
>only one sector of the directory may have been written, destroying
>the catalogue!
> 
>  
>
What if the user presses break, what if I _dont_ set up an Escape handler
and the user presses Escape. What if a program is in a long loop (doing
file stuff) and the user presses Escape and nothing happens? they'll press
Break and make just as much of a mess.

I _wont_ escape during a file delete, file delete can only occur due to 
a call
to an OS function, which are protected from Escape. In which situation
the exit will be delayed until the os function returns.

>>so it means hanging off the interrupt vector somewhere. Also
>>there is no way of returning from BRK so I'm setting something
>>    
>>
> 
>There is, it's called setting up an error handler. In machine code
>you do it by setting BRKV to point to you error handler. In BASIC
>you do it by using ON ERROR.
> 
>  
>
I was merely trying to put it into no OS specific terms that Uz et al would
get as they are non BBC types

It looks as if there are two camps on this, those that dont want any form of
out-of-band signals sue to escape and those that do. I think I may put 
all this
stuff in the BBC library but have it compile-time switchable some how 
(either
when compiling the end program or when compiling the library).

Cheers

Dom
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