Re: NSOutlineView threading problem

FROM : Adam R. Maxwell
DATE : Mon Jun 16 18:05:54 2008

On Jun 16, 2008, at 11:17 AM, j o a r wrote:

>
> On Jun 16, 2008, at 7:44 AM, David wrote:
>

>> While I've been investigating this, I have found more documentation 
>> on
>> thread safety issues in the "Threading Programming Guide". I'd read 
>> it
>> before but it helps to re-read. It says that NSView classes ARE 
>> thread
>> safe... to an extent.

>
>
> Very interesting that it says that NSView is "generally thread-
> safe", but then immediately afterwards limits you to "perform other 
> operations [...] only from the main thread". Note the "other", which 
> is as broad in scope as the "generally" used earlier. I'm going to 
> file an enhancement request for improved documentation here.
>
> I think that what they want to call out there is that you can draw 
> from background threads. I could be wrong, but I don't think that 
> you should read more into it than that.


This level of vagueness is persistent throughout the framework docs, 
though, and gives them an absolute value |v| < 0 with respect to 
threading (my opinion, of course).  And yes, I know the "file a bug 
report" mantra, but a) I don't get paid for filing bug reports, and b) 
it can take years even for a doc bug to be fixed (my oldest is from 
2005, but I expect it's just forgotten).

Quotes from the docs:
"For the most part, the Application Kit is not thread safe; in 
particular, Cocoa bindings and controllers are not thread safe—if you 
are using these technologies, multi-threading may be complex." [1]

Now juxtapose that with this statement:

"For example, the Application Kit is generally thread-safe, but its 
text system (consisting of NSText, NSTextView,NSLayoutManager, 
NSTextStorage, and related classes) is not thread-safe if the layout 
of text is done asynchronously." [2]

So can you draw text to a bitmap context in a background thread? 
Sure; use NSStringDrawing, or use NSLayoutManager directly with 
background layout disabled.  Only the latter option is (sort of) 
documented and /only in the header/.

If you want to (say) open a URL from a secondary thread, can you use -
[NSWorkspace openURL:]?  Apparently not, but it's not in either list 
[3].  Until recently, NSURL was on the thread-unsafe list, so maybe 
that was the answer...

However, can you use LaunchServices?  Certainly!  It says so, right in 
the API docs for LSOpenCFURLRef: "Thread-safe since Mac OS version 
10.2." [4].  Perfect.  So if you want thread safety, use Carbon since 
it tends to have explicit documentation ;).

This ambiguity also bites Apple, I think.  For instance, prior to 
10.5, SearchKit (which is documented to be thread safe) would crash 
using NSAttributedString to read certain files (XML/HTML, IIRC). 
NSImage caching has also been mentioned on this list as the source of 
crashes, yet it's documented to be thread safe.

regards,
Adam

[1]
http://developer.apple.com/documentation/Cocoa/Conceptual/CoreData/Articles/cdMultiThreading.html

[2] http://developer.apple.com/documentation/UserExperience/Conceptual/Quicklook_Programming_Guide/QLImplementationOverview/chapter_5_section_4.html

[3]
http://developer.apple.com/documentation/Cocoa/Conceptual/Multithreading/ThreadSafetySummary/chapter_950_section_2.html#/
/apple_ref/doc/uid/10000057i-CH12-SW4

[4]
http://developer.apple.com/documentation/Carbon/Reference/LaunchServicesReference/Reference/reference.html_______________________________________________

Cocoa-dev mailing list (<email_removed>)

Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com

Help/Unsubscribe/Update your Subscription:
http://lists.apple.com/mailman/options/cocoa-dev/<email_removed>

This email sent to <email_removed>