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Re: iOS: Preventing a singleton from being deallocated when the app is in the background.
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Re: iOS: Preventing a singleton from being deallocated when the app is in the background.


  • Subject: Re: iOS: Preventing a singleton from being deallocated when the app is in the background.
  • From: Alex Zavatone <email@hidden>
  • Date: Wed, 19 Oct 2016 14:54:30 -0500

On Oct 19, 2016, at 2:08 PM, Steve Christensen wrote:

> This is the model I use for singletons and I've never had the singleton instance deallocated out from under me.
>
> + (MyClass*) sharedThing
> {
> 	static dispatch_once_t sOnceToken = 0;
> 	static MyClass* sSharedThing = nil;
>
> 	dispatch_once(&sOnceToken,
> 	^{
> 		sSharedThing = [[MyClass alloc] init];
> 	});
>
> 	return sSharedThing;
> }
>

It appears that this is what I am doing.  Though the details are not the same, should this matter?

We have already had to patch one instance where the ref to this was getting lost

+ (instancetype)referenceGeofenceController {
   static GeofenceControllerSingleton *geofenceController;
   static dispatch_once_t onceToken;

   dispatch_once(&onceToken, ^{
       geofenceController = [[self alloc] init];
   });
   return geofenceController;
}


Is there anything wrong with what I'm doing?  should I be using [GeofenceControllerSingleton alloc] init] instead of [[self alloc] init]?

Thanks a million.
Alex Zavatone

>
>
>> On Oct 19, 2016, at 11:41 AM, Alex Zavatone <email@hidden> wrote:
>>
>> We are running into what appears to be a case where a singleton that has been created through GCD dispatch_once may be getting deallocated by the OS.
>>
>> To check and see if this is the case, I have put logging code in the dealloc method, but our logs do show the init method being called twice even though the method is past the dispatch_once.
>>
>> I'm interested in seeing if I can prevent the singleton from being deallocated.
>>
>> I have seen on discussion where people suggest keeping a private strong property in the singleton with a reference to self to prevent this from happening.
>>
>> Something like
>>   self.selfReference = self;
>>
>> within an interface extension.
>>
>> Naturally, this is raising some eyebrows with other members of the team, but currently, no one has a solution to make sure that this core singleton doesn't get deallocated when the app is in the background and has been running for a while.
>>
>> Does this sound sane or a horrible idea?
>>
>> If it does sound like a horrible idea, how would you suggest preventing an important singleton from being deallocated?
>>
>> Thanks in advance,
>> Alex Zavatone
>


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  • Follow-Ups:
    • Re: iOS: Preventing a singleton from being deallocated when the app is in the background.
      • From: Steve Christensen <email@hidden>
    • Re: iOS: Preventing a singleton from being deallocated when the app is in the background.
      • From: Jens Alfke <email@hidden>
References: 
 >iOS: Preventing a singleton from being deallocated when the app is in the background. (From: Alex Zavatone <email@hidden>)
 >Re: iOS: Preventing a singleton from being deallocated when the app is in the background. (From: Steve Christensen <email@hidden>)

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