Re: iOS: Preventing a singleton from being deallocated when the app is in the background.
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: Steve Christensen <email@hidden>
- Date: Wed, 19 Oct 2016 14:29:43 -0700
The only difference between your code and mine is that you haven't initialized onceToken = 0 so it has a random value.
I looked around to see if that makes a difference and didn't get much confirmation one way or another. One by Mike Ash (https://www.mikeash.com/pyblog/friday-qa-2014-06-06-secrets-of-dispatch_once.html) mentions, "Note that dispatch_once_t is just a typedef for long, initialized to zero, and with the meaning of other values left up to the implementation."
It's a simple thing to change to see what happens.
> On Oct 19, 2016, at 12:54 PM, Alex Zavatone <email@hidden> wrote:
>
> 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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