Re: [Openexr-devel] Re: Mac stuff

[Paul Schneider]

Hi, Derek,

> On OS X, the stack is practically only limited by your swap space.

Is that true?  We've had problems with large stack-based arrays  
crashing on OS X inside the Piz compressor, even when building with  
gcc.  The only documentation I could find on the issue was this:

http://developer.apple.com/techpubs/macosx/DeveloperTools/MachORuntime/ 
2rt_powerpc_abi/chapter_3_section_4.html

This seems to suggest that the stack size is fixed even on X (and even  
in the Mach-O runtime), but it could be out of date.

My understanding is that the stack size is fixed, but the compiler is  
supposed to automatically set the stack size to the largest stack value  
ever needed.  This breaks down if you're developing a shared library,  
because stack size is inherited from the host app in that case.  This  
is how CFM worked on OS 9, and I was under the impression that this was  
still true on OS X.

If my understanding is incorrect, it would be good to know.  Currently,  
the Piz compressor allocates some big arrays in the heap in the OS X  
builds, but places them on the stack when building for other targets.   
This is somewhat of a performance hit, so if it's unnecessary, please  
let me know.

If stack size turns out to really be an issue on OS X, we'll probably  
change HalfLut's array to an auto_ptr in the OS X builds, so that  
developers don't have to worry about creating HalfLuts on the stack.

- Paul