[M3devel] pthreads on FreeBSD, was: endless exception loop on FreeBSD

[Tony Hosking]

Ah!  Lights turning on in my head...

It is probably the case that you have neglected to tell the compiler  
to avoid using global exception information.  You need to set  
Global_handler_stack FALSE in m3middle/src/Target.m3 for the pthreads- 
based targets.

On Dec 23, 2007, at 10:36 AM, Olaf Wagner wrote:

>>> On Dec 21, 2007, at 7:22 AM, Olaf Wagner wrote:
>>>
>>>> I'm trying to add pthread support to the FreeBSD4 platform.
>>>> My first tentative additions now lead to endless exception loops
>>>> once any error is encountered until the stack overflows.
>>>>
>>>> Does anybody know what's wrong here? I'm not aware that I have
>>>> changed anything in this area.
>>>
>> I seems that I have been linking against a non-reentrant libc. I can
>> now get a little
>> farther:
>>
>> % ./m3-sys/cm3/FreeBSD4/cm3 -help @M3debugthreads
>> Stopping from act=0x8a93500
>> Stopping act=0x8a93b80
>> Stopped act=0x8a93b80
>> Stopped from act=0x8a93500
>> Processing act=0x8a93500
>> Processing act=0x8a93b80
>> Starting from act=0x8a93500
>> Starting act=0x8a93b80
>> Started act=0x8a93b80
>> Started from act=0x8a93500
>> Stopping from act=0x8a93500
>> Stopping act=0x8a93b80
>> Stopped act=0x8a93b80
>> Stopped from act=0x8a93500
>> Processing act=0x8a93500
>> Processing act=0x8a93b80
>> Starting from act=0x8a93500
>> Starting act=0x8a93b80
>> Started act=0x8a93b80
>> Started from act=0x8a93500
>> CStatus failed with errno 2
>>
>>
>> ***
>> *** runtime error:
>> ***    Unhandled exception: OSError.E
>> ***    file "../src/os/POSIX/OSErrorPosix.m3", line 50
>> ***
>>
>> Abort trap (core dumped)
>>
>> This is the compiler trying to locate cm3.cfg at different locations.
>> It doesn't find it and an OSError.E is raised, which should get  
>> caught
>> in M3File.IsReadable, but isn't. So it seems exception handling is
>> broken as soon as I use system threads. Any ideas on this one?
>
> Some additional information:
>
> It is really only the PTHREAD setting in m3core/src/thread/m3makefile
> which makes exceptions fail. If I change it and compile everything  
> again,
> I get this output from cm3:
>
> % ./m3-sys/cm3/FreeBSD4/cm3 -help @M3debugthreads
> DetermineContext: oldSP = 0xbfbfe74c
> modelSP:    0xbfbfe70c
> oldSP:      0xbfbfe74c
> frame size: 64
> CStatus failed with errno 2
> CStatus failed with errno 2
> CStatus failed with errno 2
> CStatus failed with errno 2
> CStatus failed with errno 2
> CStatus failed with errno 2
> Critical Mass Modula-3 version d5.5.0
>   last updated: 2007-12-17
>   configuration: /usr/local/cm3/bin/cm3.cfg
> [...]
>
> So all OSError.E exceptions for stat failures are caught, and there
> are no thread switches at the start of the compiler; it only sets
> up the model frame for userlevel threads.
> In contrast, system level pthreads show much activity at the start
> (why?), and the first exception terminates the compiler.
>
> I still haven't got a good explanation for this. Unfortunately,
> the FreeBSD gdb debugger does not really seem to cope well with  
> threaded
> programs... All interesting information always is unrecoverable.
>
> Olaf
> -- 
> Olaf Wagner -- elego Software Solutions GmbH
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> Germany
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