Re: Bug in CF/NSString's no-copy constructors (was Re: Use of Mac OS X 10.5 / Leopards Garbage Collection Considered Harmful)

FROM : Michael Tsai
DATE : Wed Feb 06 17:46:25 2008

On Feb 6, 2008, at 10:55 AM, Alastair Houghton wrote:

> I'll just add, publicly, that I think this probably is a bug in 
> CFString that John has found here.  That is, I don't see why 
> CFString's pointer shouldn't be traced by the collector in this 
> case (it doesn't appear to be; certainly when I try it the backing 
> buffer is released).  The problem also occurs with NSString's -
> initWithBytesNoCopy:length:encoding:freeWhenDone: et al.


I don't think this is a bug. The NSString and CFString APIs do not 
indicate that they treat the bytes as scanned memory. In fact, when 
you pass in kCFAllocatorNull you are telling CFString that you 
"assume responsibility for deallocating the buffer." At the end of -
someMethod, you haven't saved a __strong reference to the buffer, so 
the collector is allowed to free it.

--Michael