At 7:56 PM +0700 11/12/12, Gerriet M. Denkmann wrote:
- (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;
}
Here's what I usually do:
assume that _someDictionary is an instance variable initialized to
nil and never changed once initialized to non-nil
- (NSDictionary *)someDictionary;
{
if (!_someDictionary)
{
@synchronized (self)
{
if (!_someDictionary)
{
// create a temp dictionary (might take some time)
_someDictionary = temp;
}
}
}
return _someDictionary;
}
the outer if avoids the overhead of @synchronized if _someDictionary
is already created -- this is just an optimization
the inner if is necessary to resolve the race condition if multiple
threads make it past the outer one
HTH,
-Steve
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