On Mar 11, 2009, at 10:03 AM, Robert Mullen wrote:
As I have waded into the code a little more I see that this entire
struct is allocated using calloc() in an init and freed with free().
How does that work with GC? I have tried __strong and some CFRetain
and CFRelease to no avail but want to try rearranging things a
little bit there. I think the struct itself may be the problem but
would like some corroboration.
Yes, the struct itself is a problem. When the garbage collector looks
for pointers, it doesn't look inside ordinary malloc-allocated memory.
If the only pointer to your object is inside this malloc'ed struct,
the collector won't see it and may throw your object away.
You have three options:
1. Turn the struct into an Objective-C object. You can mark all of the
ivars @public to make it more struct-like, instead of adding accessor
methods everywhere. Of course, you now need to make sure the pointers
to the former struct are GC-compatible (for example, not inside other
malloc'ed structs).
2. Allocate the struct with NSAllocateCollectable(NSScannedOption|
NSCollectorDisabledOption) AND mark the object fields in the struct
with __strong. NSScannedOption tells the collector to look inside the
struct for other GC pointers. NSCollectorDisabledOption tells the
collector that you'll call free() yourself. __strong tells the
compiler to use the GC write barriers when assigning to the struct's
fields.
3. CFRetain() pointers before storing them in the struct, and CFRelease
() them afterwards. This can be easy if the struct's fields are
wrapped in accessor functions, but otherwise may be a large code
change. Beware of uncollectable cycles.
--
Greg Parker gpar...@apple.com Runtime Wrangler
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