You can use dispatch_sync. The blog post of oliver dobnigg (cocoanetics) summs
that up quite nicely:
http://www.cocoanetics.com/2012/02/threadsafe-lazy-property-initialization/
Cheers, Jörg
On Nov 12, 2012, at 2:44 PM, Tom Davie <tom.da...@gmail.com> wrote:
>
> On 12 Nov 2012, at 13:39, Marco Tabini <mtab...@me.com> wrote:
>
>>> This is completely the wrong way to implement a property. The static
>>> variable will be shared between all instances. Here's how you should be
>>> doing a lazy loaded var:
>>>
>>> @implementation MyClass
>>> {
>>> NSDictionary *_someDictionary
>>> }
>>>
>>> - (NSDictionary *)someDictionary
>>> {
>>> static dispatch_once_t justOnce;
>>> dispatch_once(&justOnce, ^
>>> {
>>> someDictionary = [[NSDictionary alloc] initWithObjectsAndKeys: ……
>>> nil];
>>> });
>>> return someDictionary;
>>> }
>>
>> I don't think this does what you think it does; my understanding is that
>> dispatch_once will execute only once for the lifetime of an app, so the code
>> you posted will only run once for the first object that requires is, and
>> then never run again, resulting in _dictionary being Nil in all other
>> instances.
>
> Very good point! My bad.
>
>> I understood the OP's request as wanting to implement a singleton, which,
>> based on your reading, may not be the case. dispatch_once will be fine for a
>> singleton, but if you need a thread-safe, lazily-instantiated read-only
>> property, maybe something like this will do the trick:
>
> I'm pretty sure he doesn't want a singleton, as he was talking about a
> property. And yeh, sorry about the misinformation there!
>
>>
>> @implementation MyClass {
>> NSDictionary *_someDictionary
>> }
>>
>> - (NSDictionary *) someDictionary {
>> @synchronized(self) {
>> if (!_someDictionary) {
>> _someDictionary = [[NSDictionary alloc] initWith… ]
>> }
>> }
>>
>> return _someDictionary;
>> }
>
>
> _______________________________________________
>
> Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)
>
> Please do not post admin requests or moderator comments to the list.
> Contact the moderators at cocoa-dev-admins(at)lists.apple.com
>
> Help/Unsubscribe/Update your Subscription:
> https://lists.apple.com/mailman/options/cocoa-dev/j_simon%40mac.com
>
> This email sent to j_si...@mac.com
_______________________________________________
Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com
This email sent to arch...@mail-archive.com
