Re: is NSNotificationCenter thread safe?
Re: is NSNotificationCenter thread safe?
- Subject: Re: is NSNotificationCenter thread safe?
- From: Chuck Hill <email@hidden>
- Date: Wed, 4 Jun 2008 13:42:04 -0700
On Jun 4, 2008, at 1:30 PM, Florijan Stamenkovic wrote:
On Jun 04, 2008, at 13:32, Chuck Hill wrote:
On Jun 4, 2008, at 1:56 AM, Freddie Tilley wrote:
Is the java version of NSNotificationCenter thread safe?
What do you mean? What are you doing, and what do you expect the
results to be?
Yes, it is used by WebObjects internally to broadcast EOF and other
changes across threads.
And does it support posting from on thread to another similiar the
Object-C version of NSDistributedNotificationCenter
Notifications are broadcast in the same thread context that they
are sent in. It is up to the threads getting the notification to
handle the appropriately for whatever work they are engaged in. I
am not sure if that answers your question or not.
Chuck, could you clarify? I'm not sure I read you right. It is my
assumption that the notification center does not do any thread
handling whatsoever. Basically that the callback method is called on
the same thread that posted the notification, without even
considering any other threads involved. Is that what you're saying?
Yes. Along with the fact that the receiving object needs to be aware
that some other thread will call that method while it is executing and
handle it appropriately. In the case of an EC, if it is locked, it
queues the notifications until it is unlocked. Simple synchronization
would suffice in other cases. But you need to be aware of concurrency
when receiving notifications. That should be obvious, but I have
managed to overlook some of the implications from time to time.
I've always thought NSNotification center is a rather simple,
straight-forward player.
It is, but a threaded, concurrent environment can hold many
interesting surprises ("oh right, this page is not in an R-R loop when
that notification arrives"). :-)
Chuck
--
Practical WebObjects - for developers who want to increase their
overall knowledge of WebObjects or who are trying to solve specific
problems.
http://www.global-village.net/products/practical_webobjects
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