Re: NSHashTable with weak objects crashing

[Jordan Schidlowsky]

Oooo. That’s a nice one.    I can test this one as I can usually reproduce it 
kinda randomly in our game.

Sent from my iPhone

> On Jul 31, 2019, at 3:28 AM, David Chisnall <theraven@theravensnest.org> 
> wrote:
> 
>> On 30/07/2019 09:17, David Chisnall wrote:
>> As I commented on the issue, I believe that one is caused by having too many 
>> hash collisions and the table being unable to resize.  I plan at some point 
>> to replace the hash table implementation, which should fix that issue.
>> If anyone has a test case for reproduceable segfaults, please file an issue 
>> on GitHub.
> 
> While replacing the hash table, I managed to turn it into a reproduceable 
> fault on at least one machine.  The bug is quite subtle:
> 
> We have a map from objects to weak reference structures.
> The weak reference structure points to the object.
> When we delete the last weak reference, we delete the object from the map.
> We delete the object from the map using the object as the key.
> But by the time a weak reference is deallocated, its object pointer has been 
> zeroed...
> ...so we always remove a random element from the map and leave a dangling 
> pointer in the table.
> 
> David
> 
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