[fpc-pascal] writeln: FPC runtime race conditions in external C threads

[Alexander Grau]

Am 12.07.2010 um 13:24 schrieb Michael Van Canneyt:

>
>
> Basically, any heap memory access and standard pascal I/O are  
> forbidden in
> threads started outside FPC, because the necessary thread structures  
> are not
> initialized correctly.

Is my assumption correct that this means I cannot use much of FPC  
then?  As far as I can see, calling an object seems to be possible  
without any crash (aren't these on the heap too ?).

Due to these limitations, I think the best then would be to switch  
from the C callback thread into the FPC thread - how would that be  
(safely) possible?



>
>
> Michael.
>
> On Mon, 12 Jul 2010, Alexander Grau wrote:
>
>> Hello,
>>
>> While using an external C framework (Mac OS X, discrecording OS  
>> framework, FPC 2.4), I noticed that my FPC console app crashes when  
>> I use writeln's in both C threads (callbacks).
>>
>> Example:  Two FPC functions that are called from an external C  
>> library (c_callback1 and c_callback2) - callback2 is called within  
>> callback1 in another C thread (other than the FPC main thread).
>>
>>
>> // called from external C framework within the FPC main thread
>> c_callback1; cdecl;
>> begin
>> writeln('callback1begin');
>> // c_ callback2 is called here from another C thread
>> writeln('callback1end');   <==   my FPC console app crashes here  
>> ( "EInOutError - Disk Full")
>> end;
>>
>>
>> // called from external C framework in another C thread
>> c_callback2; cdecl;
>> begin
>> writeln('callback2begin');
>> writeln('callback2end');
>> end;
>>
>> An unhandled exception occurred at $000669E3 :
>> EInOutError : Disk Full
>> $000669E3  CALLBACK1,  line xxx
>>
>>
>> Question:    Why isn't it safe to call writeln's in non-FPC  
>> threads? Are there any other FPC runtime functions I should not  
>> call within non-FPC threads?
>>
>> I'm going to make an FPC wiki page ('Threading Pitfalls')  that  
>> will discuss these and other issues related to threading and I  
>> welcome all explanations on this so I can better understand this  
>> problem! :-)
>>
>> Thanks,
>> Alexander
>>
>> _______________________________________________
>> fpc-pascal maillist  -  fpc-pascal at lists.freepascal.org
>> http://lists.freepascal.org/mailman/listinfo/fpc-pascal
> _______________________________________________
> fpc-pascal maillist  -  fpc-pascal at lists.freepascal.org
> http://lists.freepascal.org/mailman/listinfo/fpc-pascal

Best regards / Mit freundlichen Grüßen/順致最崇高的敬意
Alexander Grau

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