On May 4, 2010, at 15:09, Jens Alfke wrote:
>> 2. What does "thread-safe" mean in this context? I would take it to mean
>> that *any* single instance allocated with [[NSFileManager alloc] init] can
>> be used by *any* thread. Or does it mean that each thread needs a unique
>> instance, but such instances happily co-exist?
>
> The latter, I think.
That's what I was starting to think too, except for the *absolute* assertion to
the contrary in the Threaded Programming Guide, which I quoted before:
http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/Multithreading/ThreadSafetySummary/ThreadSafetySummary.html
> The following classes and functions are generally considered to be
> thread-safe. You can use the same instance from multiple threads without
> first acquiring a lock.
>
> [...]
> • NSFileManager (in Mac OS X v10.5 and later)
That's pretty clear. Unless it's wrong.
>> 3. If any single instance allocated with [[NSFileManager alloc] init] is
>> thread-safe in the fullest sense, why doesn't [NSFileManager defaultManger]
>> just return one of these, so that it can be (considered) thread-safe too?
>
> Because then you wouldn't be able to set a delegate on the shared instance
> and have it be used on all calls involving that instance (which is the most
> common case.)
Well, you can't set a delegate on *any* instance if anything else might also do
so. So that explains why there can be multiple instances, not why the default
instance isn't as thread-safe as the others (if it isn't, and if they are).
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