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POMultiple Operation Queues with Different priorities
 

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  1. POMultiple Operation Queues with Different priorities
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    <p>Good day, here's what i am trying to do:</p> <ul> <li>i have a photo processing app that takes images using AVFoundation</li> <li>i have a DeviceMotion queue that is processing device position at 60Hz</li> <li>when image is taken, it needs to be cropped and saved. DeviceMotion needs to keep running and interface updated without delays</li> </ul> <p>what i am seeing is: updates to interface from DeviceMotion queue are being frozen for the duration of image crop.</p> <p>this is how i start updates for DeviceMotion:</p> <pre><code>self.motionManager.deviceMotionUpdateInterval = 1.0f/60.0f; gyroQueue = [[NSOperationQueue alloc] init]; [self.motionManager startDeviceMotionUpdatesToQueue:gyroQueue withHandler:^(CMDeviceMotion *motion, NSError *error){ [NSThread setThreadPriority:1.0]; [self processMotion:motion withError:error]; }]; </code></pre> <p>when images is returned from AVFoundation it is added to the queue for processing:</p> <pre><code>imageProcessingQueue = [[NSOperationQueue alloc] init]; [imageProcessingQueue setName:@"ImageProcessingQueue"]; [imageProcessingQueue setMaxConcurrentOperationCount:1]; //[imageProcessingQueue addOperationWithBlock:^{ //[self processImage:[UIImage imageWithData:imageData]]; //}]; NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(processImage:) object:[UIImage imageWithData:imageData]]; [operation setThreadPriority:0.0]; [operation setQueuePriority:NSOperationQueuePriorityVeryLow]; [imageProcessingQueue addOperation:operation]; </code></pre> <p>and the method for processing the image:</p> <pre><code>- (void)processImage:(UIImage*)image { CGSize cropImageSize = CGSizeMake(640,960); UIImage *croppedImage = [image resizedImageWithContentMode:UIViewContentModeScaleAspectFit bounds:cropImageSize interpolationQuality:kImageCropInterpolationQuality]; NSData *compressedImageData = UIImageJPEGRepresentation(croppedImage, kJpegCompression); [self.doc addPhoto:compressedImageData]; } </code></pre> <p>the issue is: </p> <ul> <li>devicemotion updates are blocked for the duration of image crop when image is processed using the NSOperationQueue</li> </ul> <p>if i process the image using performSelectorInBackground - it works as desired (no delays to DeviceMotion queue)</p> <blockquote> <pre><code>[self performSelectorInBackground:@selector(processImage:) withObject:[UIImage imageWithData:imageData]]; </code></pre> </blockquote> <p>any ideas on where my understanding of background threading needs an update? :) </p> <p>PS. I have asked this question earlier but it got nowhere, so this is a re-post</p>
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    1. USAndrei G.
    1. USAndrei G.
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    1. COwhere are you setting `queuePriority` on your operation queue?
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      1. USnielsbot
    2. COi am setting queuePriority on the NSInvocationOperation, see updated code above...
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      1. USAndrei G.
    3. COwhy are you setting the priority to `0.0` and not one of `NSOperationQueuePriorityVeryHigh` or `NSOperationQueuePriorityVeryHigh`? `0` (not a float) is the standard priority.
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