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Re: [[NSFileManager alloc] init] considered thread-safe
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Re: [[NSFileManager alloc] init] considered thread-safe


  • Subject: Re: [[NSFileManager alloc] init] considered thread-safe
  • From: Jens Alfke <email@hidden>
  • Date: Tue, 4 May 2010 15:09:37 -0700


On May 4, 2010, at 2:03 PM, Quincey Morris wrote:

1. Why are the additional instances only "considered" thread-safe. Doesn't anyone know?

I think it's using "considered" in a definite sense.

2. What does "thread-safe" mean in this context? I would take it to mean that *any* single instance allocated with [[NSFileManager alloc] init] can be used by *any* thread. Or does it mean that each thread needs a unique instance, but such instances happily co-exist?

The latter, I think. What happened was that in 10.5 the NSFileManager was extended to have a delegate, instead of being stateless. There are obvious problems with multiple clients trying to set their own delegates on the same object, or with a call on a background thread invoking a delegate call to unrelated code that wasn't expecting to be called on that thread.


3. If any single instance allocated with [[NSFileManager alloc] init] is thread-safe in the fullest sense, why doesn't [NSFileManager defaultManger] just return one of these, so that it can be (considered) thread-safe too?

Because then you wouldn't be able to set a delegate on the shared instance and have it be used on all calls involving that instance (which is the most common case.)


—Jens_______________________________________________

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