Re: NSOutlineView threading problem
Re: NSOutlineView threading problem
- Subject: Re: NSOutlineView threading problem
- From: "Adam R. Maxwell" <email@hidden>
- Date: Mon, 16 Jun 2008 12:05:54 -0400
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_______________________________________________
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