Re: How to implement readonly property
Re: How to implement readonly property
- Subject: Re: How to implement readonly property
- From: Marco Tabini <email@hidden>
- Date: Mon, 12 Nov 2012 08:03:09 -0500
Looking at the docs, dispatch_once takes care of the synchronization for you:
https://developer.apple.com/library/mac/ipad/#documentation/Performance/Reference/GCD_libdispatch_Ref/Reference/reference.html
It should therefore be thread safe to use without any additional synchronization code.
Sent from my New iPad. I blame all typos on the Fruit Company. May have been dictated.
On 2012-11-12, at 7:56 AM, "Gerriet M. Denkmann" <email@hidden> wrote:
> I have a property:
>
> @property (readonly) NSDictionary *someDictionary;
>
> This property should be computed on demand, and should be accessible by several threads.
>
> My current implementation is:
>
> - (NSDictionary *)someDictionary;
> {
> static NSDictionary *someDictionary;
> static dispatch_once_t justOnce;
> dispatch_once( &justOnce, ^
> {
> // create a temp dictionary (might take some time)
> someDictionary = temp;
> }
> );
>
> return someDictionary;
> }
>
> The first thread which needs someDictionary will trigger its creation. Ok.
>
> But what happens when another thread wants to access someDictionary while it is still being created? I guess it will receive just nil.
> This would be not correct; it really should wait until the dictionary is ready.
>
> How to achieve this? Use a lock? Use @synchronize?
>
> 10.8.2 with Arc.
>
>
> Gerriet.
>
>
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