[gccsdk] Threading + Alt-Break = Trashed Computer

Rien Mertens rien.mertens at hccnet.nl
Sat Jul 12 13:26:31 PDT 2008

In message <febad0bd4f.Jo at hobbes.bass-software.com>
          John Tytgat <John.Tytgat at aaug.net> wrote:

> In message <66f698bd4f.Rien at rien/mertens.hccnet.nl>
>           Rien Mertens <rien.mertens at hccnet.nl> wrote:
>> I my opinion this might very well be related to the newer RISC OS
>> versions; my RiscPC with RO4.02 does a better job to recover from an
>> error with ALT_Break than my A9Home with RO4.42, which is much less
>> successful in recovering with ALT_Break. It often fails and results in
>> a a stiffed machine without the keyboard or mouse usable anymore,
>> b or a machine that can only be reset with the choice CTRL-Break or
>> red button..
> What we know so far is that this watchdog bug can only be triggered when you
> kill a task which is not the current task, i.e. when you have to click one
> or more times on 'Next' after pressing <Alt><Break>.  And whether or not this
> really leads to system instability afterwards depends on the task itself you
> killed, i.e. whether it really needs to have its Exit handler called or
> not.
> So it would be interesting if you could test both OS versions concerning
> stability but each time killing the first task avoiding this bug at all.
> We enabled the Pre/Post filter code in UnixLib only one year ago
> (08 July 2007, both in GCCSDK 3.4.6 r3 as in GCCSDK 4) so basically from
> that moment on we need to have our Exit handler called for pthread using
> programs.  So killing an UnixLib based program using pthreads (like e.g.
> Firefox) when it was not the current task made that this watchdog bug will
> bring the system down shortly after it.  Before that date, you got away it.
> At the time you were using RO4.02 it could be very well be that there were
> no programs around (or in use by you) which would suffer from this very
> same problem.  And that you now use a recent Firefox on your A9home which
> can trigger this problem...
> With other words, so far I'm not convinced that a change in RISC OS is
> causing more problems with <Alt><Break> than before.
> John.

I can only agree with you that there is no prove of what is the cause 
of the different effects between the two machines at all.
I do not know enough about programming and what ptreads are or which 
programs make use of it and when... So I am not capable to test this, 
I suppose.

I almost never kill more than one program, only the last one that 
seemed to give a problem.

Rien Mertens
Tweeberg 1 A
5246 XL Rosmalen       0031(0)736415517

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