On Jan 26, 2009, at 14:45, Sean McBride wrote:
On 1/18/09 4:29 PM, Ben Trumbull said:
I mention this because (I'm embarrassed to admit) I never really
thought about this till yesterday. I *think* other design decisions
have made the atomic-ness irrelevant to any of the code I've
written,
but now I need to go back and check, especially where Core Data is
involved.
Core Data @dynamic properties are always nonatomic, irrespective of
the property declaration.
Core Data explicitly, intentionally, and states in the documentation,
that you can have any property atomicity you want so long as it's
nonatomic.
Interesting. I never thought about this either, and was happy to see
this come up.
BTW, continuing the theme of things I didn't think about ...
Although the rationale for non-atomicity runs under the general thread-
safety discussion umbrella, there are actually two separate issues to
consider.
Generally, discussion about thread-safety of data like Core Data
properties centers around the possibility of conflicting changes from
multiple threads. Atomicity at the property level doesn't really help
with that (as stated), and the problem must be solved at a higher level.
However, even if only one thread can be changing the data, atomicity
still matters. If the accessors aren't atomic, multiple read-only
users of the data (in different threads) might get completely bogus
results. This problem *can* be solved by atomicity at the property
level, if you're prepared to take the potential performance hit from
implementing it.
I have to keep reminding myself that serializing changes through a
single thread does *not* provide thread safety unless there is
atomicity too.
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