Re: Thread safe?

FROM : Adam R. Maxwell
DATE : Sat Mar 29 20:48:47 2008

On Mar 29, 2008, at 12:20 PM, Trygve Inda wrote:
>

>>> How about:
>>>
>>> NSImage *    image = [[[NSImage alloc] initWithContentsOfFile:path]
>>> autorelease];

>>

[...]
>>
>> Drawing into an NSImage is explicitly documented to be thread safe in
>> the article you linked to,

>
> I guess I was more concerned with the initWithContentsOfFile:path


For my own code, I'd tend to assume it's safe since it should just be 
a wrapper around ImageIO.  However, sometimes Cocoa adds an unexpected 
layer of thread-unsafety (e.g. NSRunLoop vs. CFRunLoop), and the Cocoa 
API docs aren't as helpful as the Carbon ones for thread safety.

>> 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:.

>
> This could work, but as I need to do pixel level manipulation, I 
> really need
> to know the exact format of the bitmap and this does not seem to let 
> me
> specify it.


That makes sense.  You could also introspect the returned imagerep and 
see if it matches your desired format, then only redraw it if 
necessary.  For messing with pixels, I'd avoid NSImage altogether and 
just use ImageIO to create a CGImage, then draw that into your 
NSBitmapImageRep with [[NSGraphicsContext 
graphicsContextWithBitmapImageRep:] graphicsPort] as the CGContext.

--
adam
On Mar 29, 2008, at 12:20 PM, Trygve Inda wrote:
>

>>> How about:
>>>
>>> NSImage *    image = [[[NSImage alloc] initWithContentsOfFile:path]
>>> autorelease];

>>

[...]
>>
>> Drawing into an NSImage is explicitly documented to be thread safe in
>> the article you linked to,

>
> I guess I was more concerned with the initWithContentsOfFile:path


For my own code, I'd tend to assume it's safe since it should just be 
a wrapper around ImageIO.  However, sometimes Cocoa adds an unexpected 
layer of thread-unsafety (e.g. NSRunLoop vs. CFRunLoop), and the Cocoa 
API docs aren't as helpful as the Carbon ones for thread safety.

>> 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:.

>
> This could work, but as I need to do pixel level manipulation, I 
> really need
> to know the exact format of the bitmap and this does not seem to let 
> me
> specify it.


That makes sense.  You could also introspect the returned imagerep and 
see if it matches your desired format, then only redraw it if 
necessary.  For messing with pixels, I'd avoid NSImage altogether and 
just use ImageIO to create a CGImage, then draw that into your 
NSBitmapImageRep with [[NSGraphicsContext 
graphicsContextWithBitmapImageRep:] graphicsPort] as the CGContext.

--
adam