Re: Thread safe?

FROM : Adam R. Maxwell
DATE : Sat Mar 29 18:54:28 2008

On Mar 29, 2008, at 6:44 AM, Trygve Inda wrote:
> I am finding it hard to determine in many cases exactly what is 
> thread safe
> as this is not complete:
>
> http://developer.apple.com/documentation/Cocoa/Conceptual/Multithreading/Thr
> eadSafetySummary/chapter_950_section_2.html
>
> Can I call the following from a thread?
>
> segImageRep = [[NSBitmapImageRep alloc] initWithBitmapDataPlanes:NULL
>                              pixelsWide:100
>                              pixelsHigh:100
>                              bitsPerSample:8
>                              samplesPerPixel:4
>                              hasAlpha:YES
>                              isPlanar:NO
>                              colorSpaceName:NSDeviceRGBColorSpace
>                              bitmapFormat:NSAlphaFirstBitmapFormat
>                              bytesPerRow:100 * 4
>                              bitsPerPixel:32];
>    segBaseAddr = [segImageRep bitmapData];


Yes.  See

http://www.cocoabuilder.com/archive/message/cocoa/2007/11/15/193191

ISTR having problems specifying a nonzero bytesPerRow and passing NULL 
for the bitmap data, so you might need to either manage the buffer 
yourself or pass zero for bytesPerRow to allow NSBitmapImageRep to pad 
it appropriately.

>
>    [segImageRep dealloc];


You should never call dealloc directly (well, unless you've overridden 
-retain/-release to handle your own refcounting).

> How about:
>
> NSImage *    image = [[[NSImage alloc] initWithContentsOfFile:path]
> autorelease];
>
>    [NSGraphicsContext saveGraphicsState];
>    [NSGraphicsContext setCurrentContext:[NSGraphicsContext
> graphicsContextWithBitmapImageRep:segImageRep]];
>
>    [image drawInRect:NSMakeRect(0, 0, [image size].width, [image
> size].height) fromRect:NSMakeRect(0, 0, [image size].width, [image
> size].height) operation:NSCompositeCopy fraction:1.0];
>
>    [NSGraphicsContext restoreGraphicsState];


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:.

--
adam
On Mar 29, 2008, at 6:44 AM, Trygve Inda wrote:
> I am finding it hard to determine in many cases exactly what is 
> thread safe
> as this is not complete:
>
> http://developer.apple.com/documentation/Cocoa/Conceptual/Multithreading/Thr
> eadSafetySummary/chapter_950_section_2.html
>
> Can I call the following from a thread?
>
> segImageRep = [[NSBitmapImageRep alloc] initWithBitmapDataPlanes:NULL
>                              pixelsWide:100
>                              pixelsHigh:100
>                              bitsPerSample:8
>                              samplesPerPixel:4
>                              hasAlpha:YES
>                              isPlanar:NO
>                              colorSpaceName:NSDeviceRGBColorSpace
>                              bitmapFormat:NSAlphaFirstBitmapFormat
>                              bytesPerRow:100 * 4
>                              bitsPerPixel:32];
>    segBaseAddr = [segImageRep bitmapData];


Yes.  See

http://www.cocoabuilder.com/archive/message/cocoa/2007/11/15/193191

ISTR having problems specifying a nonzero bytesPerRow and passing NULL 
for the bitmap data, so you might need to either manage the buffer 
yourself or pass zero for bytesPerRow to allow NSBitmapImageRep to pad 
it appropriately.

>
>    [segImageRep dealloc];


You should never call dealloc directly (well, unless you've overridden 
-retain/-release to handle your own refcounting).

> How about:
>
> NSImage *    image = [[[NSImage alloc] initWithContentsOfFile:path]
> autorelease];
>
>    [NSGraphicsContext saveGraphicsState];
>    [NSGraphicsContext setCurrentContext:[NSGraphicsContext
> graphicsContextWithBitmapImageRep:segImageRep]];
>
>    [image drawInRect:NSMakeRect(0, 0, [image size].width, [image
> size].height) fromRect:NSMakeRect(0, 0, [image size].width, [image
> size].height) operation:NSCompositeCopy fraction:1.0];
>
>    [NSGraphicsContext restoreGraphicsState];


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:.

--
adam