driver_output_term() and unsigned long (32 bit) values

Shawn Pearce <>
Fri Jul 26 17:18:46 CEST 2002


Per Bergqvist <> scrawled:
> > For what it's worth, it doesn't appear possible to have the driver  
> > create a reference and send that back to Erlang, either.            
> >                                                                     
> IMHO, I think it is a bad idea to allow a driver to create a reference
> since references should be unique and it will be hard to guarantee    
> uniqueness if there are several allocators ...                        

Why not a function:

	ErlDrvTerm driver_mkref()

which will always use the internal reference allocator?  Or is it
not possible to use the existing allocator underlying erlang:mkref/0
while a driver is executing?

It would be very convient for drivers to be able to use references,
esp. as the references could be stored in a small hash table linking
to driver specific objects, for example a widget in a GUI library.

Of course, driver authors could still try to send illegal reference
values by attempting to create their own references without the
driver_mkref() function.  But today driver authors could also try to
make an ErlDrvBinary on their own without driver_alloc_binary(), and
the results would be just as bad.

I had really considered making a bunch of ErlDrvBinary objects in a
mmap region at one point, until I noticed in the Erts source that the
ErlDrvBinary is not the entire binary structure - there is data stored
before it by the emulator.  I would have had pretty ugly results had
I tried to use my own binary.

Therefore I'm arguing that its acceptable if there are ugly results
because a driver author used a value for a reference which did not
come from driver_mkref().

--
Shawn.

Why do I like Perl?  Because ``in accordance with Unix tradition Perl
gives you enough rope to hang yourself with.''

Why do I dislike Java? Because ``the class ROPE that should contain the
method HANG to do the hanging doesn't exist because there is too much
'security' built into the base language.''



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