I've just been looking back at some code that has been working fine for me for
a while, and as far as I can see it shouldn't actually work! I'd be interested
for peoples' comments. The code is as follows:
dispatch_async(queue1,
^{
NSImage *theImage = [frame GetNSImage];
NSData *tiffRep = [theImage TIFFRepresentation];
dispatch_async(queue2,
^{
[tiffRep writeToFile:[NSString stringWithFormat:@"%...@%d.tif",
[[frame Camera] ExportFilePrefix],
[frame FrameNumber]]
atomically:YES];
});
[theImage release];
});
Work running on serial queue "queue1" calculates a TIFF representation for an
image, and then schedules work on serial queue "queue2" to write that data to
disk. What I can't work out is why tiffrep isn't autoreleased as soon as the
outer block completes. Is the compiler/runtime being clever enough to retain it
because it is going to be needed in the inner block (if so: very clever!)? If
not, am I just getting lucky here with exactly when/how grand central does its
autorelease cleanup? Or maybe the TIFF representation and/or my frame data is
still being retained elsewhere for a while (possible, depending on how the
thread timings work out...).
I'm pretty new to Cocoa so I'm keen to understand this properly - I'd be
interested to hear peoples thoughts on this: is what I am doing ok, or do I
need to add some explicit retain/releasing of tiffRep?
Cheers
Jonny_______________________________________________
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