Re: Thread safe?

FROM : Adam R. Maxwell
DATE : Sun Mar 30 17:01:16 2008

On Mar 30, 2008, at 6:10 AM, Thomas Engelmeier wrote:
>
> On 29.03.2008, at 18:54, Adam R. Maxwell wrote:

>>
>> Drawing into an NSImage is explicitly documented to be thread safe 
>> in the article you linked to, and each thread has its own graphics 
>> context.  The post I linked to does indicate that you might want to 
>> use [image setCacheMode:NSImageCacheNever].  If your goal is just 
>> to get an NSBitmapImageRep from a file, it's probably easier just 
>> to use +imageRepWithContentsOfFile:.

>
> While it is documented to be thread save you might get crashes later 
> when an NSBitmapImageRep created by drawing into from an secondary 
> thread gets drawn itself. The crash occurs when the image tries to 
> access an NULL (offscreen) window context (it probably was 
> originally drawn into).
>
> Tried to debug that on 10.5.2 (and simply worked around)...


That's interesting.  Was it an NSBitmapImageRep or NSImage/
NSCachedImageRep?  I didn't think a bitmap context would be associated 
with a window context like that.  Either way it doesn't sound good, 
though.

--
adam


On Mar 30, 2008, at 6:10 AM, Thomas Engelmeier wrote:
>
> On 29.03.2008, at 18:54, Adam R. Maxwell wrote:

>>
>> Drawing into an NSImage is explicitly documented to be thread safe 
>> in the article you linked to, and each thread has its own graphics 
>> context.  The post I linked to does indicate that you might want to 
>> use [image setCacheMode:NSImageCacheNever].  If your goal is just 
>> to get an NSBitmapImageRep from a file, it's probably easier just 
>> to use +imageRepWithContentsOfFile:.

>
> While it is documented to be thread save you might get crashes later 
> when an NSBitmapImageRep created by drawing into from an secondary 
> thread gets drawn itself. The crash occurs when the image tries to 
> access an NULL (offscreen) window context (it probably was 
> originally drawn into).
>
> Tried to debug that on 10.5.2 (and simply worked around)...


That's interesting.  Was it an NSBitmapImageRep or NSImage/
NSCachedImageRep?  I didn't think a bitmap context would be associated 
with a window context like that.  Either way it doesn't sound good, 
though.

--
adam