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Re: Thread::Use - use a module inside a thread only

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From:
Arthur Bergman
Date:
July 30, 2002 06:28
Subject:
Re: Thread::Use - use a module inside a thread only
Message ID:
253A33B4-A3C0-11D6-8235-003065D64CBE@contiller.se

On tisdag, juli 30, 2002, at 03:24 , Elizabeth Mattijsen wrote:

>
> At 02:10 PM 7/30/02 +0100, Nicholas Clark wrote:
>> > As I said, as a simple solution for now, I think a:
>> >    sub CLONE { undef( %PerlIO::gzip:: ) }
>> > or equivalent of that in XS code would be sufficient to get around 
>> the
>> > current problem of having to start your threads before you can open a
>> > PerlIO::gzip layer...
>>
>> I believe that this won't work. Nor the direct XS equivalent. It will 
>> hide
>> the problem:
>>
>> Once an IO layer is created, it is a free standing object attached to a
>> stream. It doesn't matter if you "nuke" the module in the symbol 
>> table -
>> you still have existing PerlIO structures pushed on existing streams 
>> that
>> don't get killed this way.
>
> Then maybe it should become possible to indicate that a PerlIO 
> _structure_ should never be cloned?  So it never gets to the part where 
> it attempt to clone it?
>
>
>> And the PerlIO system defaults to doing a shallow structure copy (much 
>> like
>> the default in C++ for copying objects) to make a copy of every layer 
>> for
>> the new chain of layers in the layer stack. And to clone safely 
>> PerlIO::gzip
>> needs to implement a deep copying constructor. And zlib doesn't provide
>> one for inflate streams (I've checked - deflateCopy copies the 
>> internal state
>> for deflation streams, and the internal state differs)
>
> So, we put in a flag that the PerlIO structure doesn't get cloned.  
> This would probably fix problems with other PerlIO:: modules...  And 
> the flag could be set by the PerlIO:: module itself!
>
> So instead of trying to find a solution to the problem, try to prevent 
> the problem from ever happening...
>
>
> (hope this made sense...)
>
>
> Liz

No, the correct approach is to clone perlio structures.


Arthur


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