Re: NSDictionary @synchronize to read multiple objects
Re: NSDictionary @synchronize to read multiple objects
- Subject: Re: NSDictionary @synchronize to read multiple objects
- From: Trygve Inda <email@hidden>
- Date: Tue, 01 Apr 2014 06:45:21 -0700
- Thread-topic: NSDictionary @synchronize to read multiple objects
> On Apr 1, 2014, at 12:25 AM, Jens Alfke wrote:
>
>> On Mar 31, 2014, at 10:16 PM, Trygve Inda <email@hidden> wrote:
>>
>>> I need to be able to set a new myDict and not have it happen between the
>>> reading of different values from the dictionary by other threads.
>>
>> Don’t expose the dictionary in mutable form. You can’t make that thread-safe
>> unless all the clients voluntarily agree to do something like wrap their
>> usage with @synchronized blocks using the dictionary as a parameter.
>
> I didn't see mention of mutating the dictionary. It sounds like he's just
> using a setter to replace it (which also likely releases it, which makes it
> potentially unsafe).
>
> I agree, though, that properties should almost never be of mutable type. But
> making them immutable doesn't, by itself, create thread-safety. If nothing
> else, the owner could still mutate it while other threads are reading it.
>
> Regards,
> Ken
>
>
Yes, the property is Mutable in the host app, but after being sent to the
helper app (which has multiple threads), it could just as easily be an
NSDictioanary (non-mutable).
I just need to be 100% certain that when the helper app threads read two
values from the dictionary, that the dictionary does not change between (or
during) these two reads.
T.
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