On Mar 8, 2012, at 12:18 , CoGe - Tamas Nagy wrote:
> I should subclass NSMutableArray because I had a project which used
> NSMutableArray (calls) before, but was not thread safe. Anyway, I can't
> really understand why it would be _really_ better to implement just
> accessors, but maybe you could explain it a bit more?
Well, slap my head if I'm missing your intention, but I don't see how having an
*atomically* safe NSMutableArray helps at all. As soon as anyone in any thread
writes:
for (NSInteger i = 0; i <= atomicallySafeArray.count; i++) {
id object = [atomicallySafeArray objectAtIndex: i];
...
}
or any such construct that contains 2+ references to the array that might see a
different state of the array over time, then the code is broken and not thread
safe. This is also broken:
for (id object in atomicallySafeArray)
…
for the separate but related reason that fast enumeration will fail if the
array mutates.
Also, implementing the accessors won't solve either of these problems.
Thread safety does *not* come from atomicity. Conversely, in many cases
atomicity has no value whatsoever -- because thread safety is what's really
required.
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