Re: Question

[Laurent Michel]

On Mar 6, 2013, at 3:44 PM, David Chisnall <address@hidden> wrote:

> 
> On 6 Mar 2013, at 13:24, Laurent Michel <address@hidden> wrote:
> 
>> I went in gdb and checked. The error is raised from a call in my own code. 
>> The receiver has the proper type and the method does exist.
>> The way the code is organized mimics the frameworks I have on MacOS (5 of 
>> them). 
>> 
>> Here is the backtrace. 
>> 
>> #18 0xb7d02f8d in -[NSObject doesNotRecognizeSelector:] (self=0x80f98e4, 
>> _cmd=0xb7f71ea8, aSelector=<optimized out>) at NSObject.m:1739
>> #19 0xb7d03051 in -[NSObject forwardInvocation:] (self=<optimized out>, 
>> _cmd=0xb7f9c818, anInvocation=0x80f98e4) at NSObject.m:1753
>> #20 0xb7db6af7 in GSFFIInvocationCallback (cif=<optimized out>, 
>> retp=<optimized out>, args=<optimized out>, user=<optimized out>)
>> ---Type <return> to continue, or q <return> to quit---
>>   at GSFFIInvocation.m:629
>> #21 0xb6f85176 in ?? () from /usr/lib/i386-linux-gnu/libffi.so.6
>> #22 0xb6f85416 in ?? () from /usr/lib/i386-linux-gnu/libffi.so.6
>> #23 0xb77720a3 in +[ORFactory intVar:var:shift:] (self=0xb77f6d50, 
>> _cmd=0x8053a18, tracker=0x80f98e4, x=0x8178064, b=1) at ORFactory.m:214
>> #24 0x0804994f in __main_block_invoke (.block_descriptor=0xbffff198, i=1) at 
>> main.m:29
>> #25 0xb77730c1 in +[ORFactory intVarArray:range:with:] (self=0xb77f6d50, 
>> _cmd=0x8053a30, tracker=0x80f98e4, range=0x8160464, clo=0xbffff198)
>>   at ORFactory.m:284
>> #26 0x08048fea in main (argc=1, argv=0xbffff294) at main.m:29
> 
> So, this definitely shows that it's not finding the method.
> 
>> ORFactory is a factory class living in a shared lib ORFoundation
>> The method invoked on ORModelI (a class living in a shared lib ORModeling) 
>> is indeed there and compiled just fine, but he's not
>> finding it. 
>> 
>> Here is the method in question:
>> 
>> 
>> -(void) addConstraint: (id<ORConstraint>) cstr
>> {
>>  [_target trackConstraint:cstr];
>>  [_target add: cstr];
>> }
> 
> Is it in a category?  The class must have been loaded, if you're able to 
> create instances of it...

Nope. It is a normal method. 

> 
>> So the argument is just an "id" adopting a specific protocol.
>> 
>> The call site:
>> 
>>         if (b==0)
>> 211        return x;
>> 212     else {
>> 213        id<ORIntVar> nv = [ORFactory intVar:tracker 
>> domain:RANGE(tracker,[x min] + b,[x max] + b)];
>> 214        [tracker addConstraint:[ORFactory equal:tracker var:nv to:x 
>> plus:b annotation:DomainConsistency]];
>> 215        return nv;
>> 216     }
>> 
>> 
>> where "tracker" is an ORModelI instance
>> 
>> (gdb) po [tracker class]
>> ORModelI
>> (gdb) 
>> 
>> So far, it all looks fine. I'll decompose line 214 to check the argument 
>> being passed it (it should be a constraint (id<ORConstraint>)).
>> 
>> Right now, I'm thinking that the issue may be related to the fact that 
>> caller and callee sit in different shared libraries and this is
>> somehow causing an issue. Are there any special provisions I should be aware 
>> of when creating shared libraries on Linux that contain
>> objective-C code when I will have inheritance and categories spanning shared 
>> lib boundaries?
> 
> This should be fine, the only problems can be if the methods are in a 
> category and the category hasn't loaded.  After the start of main(), it 
> should work though.

I surmised this much as I encountered exactly that problem on iOS. But the 
issue above is with a "normal method". 
I'll debug and I'll keep you posted once I figure something out. 

All the best,

--
  Laurent



> 
> David
> 
> -- Sent from my brain
>