[Openexr-devel] Re: Mac stuff

[Paul Schneider]

> Here's some recent posts on this topic:
>
> "Help.  Can't find how to increase stack limit"
> <http://www.google.com/groups?hl=en&lr=&ie=UTF- 
> 8&safe=off&th=fa6dee68462ab47e&rnum=1>
>
> "Big Array in MachO causes Segmentation Fault"
> <http://www.google.com/groups?hl=en&lr=&ie=UTF- 
> 8&safe=off&th=9e72a986de75f4f3&seekm=3E790547.2C4FDF59%40idiom.com&fram 
> e=off>

Yes, from these it looks like the stack size is always fixed on OS X.   
One posting even touts it as a feature that helps you detect infinite  
recursion, which is sort of amusing.  It's good to know I'm correct  
about that, at any rate.


> Yeah, I'm probably wrong about that.  I do know that the heap size
> settings only apply to OS 9.  On OS X, the stack size is obviously much
> larger than the setting in the panel, but there's probably some other
> limit.

Yes, I believe I set the heap size for the confidence tests to 80 MB,  
which is somewhat arbitrary.  As you say, the heap size settings aren't  
needed for an OS X native application.

It could very well be that OS X's loader ignores the stack value in the  
'cfrg' resource (which is what OS 9 uses) and just sets the stack size  
to the default value of 512 KB, making you call setrlimit when your app  
starts up.  It would be pretty easy to write a test program to see how  
much stack space you really get by default in a CFM app on OS X.


> I have also had problems with a plugin I wrote for Final Cut Pro,  
> though that was a case where I was writing a plugin and was limited by  
> what they chose.

Yep, that's how I first ran across this problem in the Piz compressor.   
Unfortunately, using EXR in a plug-in will probably be the most common  
use on the Mac, so we'll have to keep our stack usage below the default  
in the Mac builds.  I suppose that at some point, we might be tempted  
to break OS 9 compatibility by choosing a stack requirement above 64 KB  
but below 512 KB.  Actually, I believe that until Pro 7 CodeWarrior had  
a hard-coded 32 KB stack, so that would be the practical OS 9 limit as  
most classic host applications are likely to have been built with an  
older version of CodeWarrior.  I vote for putting everything big in the  
heap :)

By the way, in case anyone is interested, there's another potential  
issue with the CFM build of IlmImfTest.  IlmImfTest creates temporary  
files called "/var/tmp/test_comp.exr" which are placed in /var/tmp in  
the mach-o builds.  Of course, CFM MSL doesn't deal with Posix paths  
and so creates a file in the directory you're running IlmImfTest from  
that is actually named "/var/tmp/test_comp.exr".  This would probably  
fail on OS X if your drive isn't HFS (I don't think filenames  
containing slashes are legal on UFS), and it could fail in the future  
on machines running OS's earlier than OS 9 if the file name becomes  
longer than 31 characters.  Just a warning to the "unofficial" OS 9  
developers out there.  Note that both of these issues are with the  
confidence app that tests the IlmImf module, and not with the core exr  
library itself.

- Paul