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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