Block leak with __block variable - ios

Question

I have a big memory leak that I have pinpointed to happen in/on requestContentEditingInputWithOptions: method. If I understand it right it happens with the img variable. If I make it __block __weak the image is nil already after I assign it (img = [UIImage...]). Am I being silly somewhere? Or how would I avoid this memory leak?
- (UIImage*) getRightlySizedImgFromAsset:(PHAsset*)asset {
__block UIImage *img;
PHContentEditingInputRequestOptions *coptions = [PHContentEditingInputRequestOptions new];
coptions.canHandleAdjustmentData = ^BOOL(PHAdjustmentData *adjustmentData) { return NO; };
//semaphore used so the block runs synchronously and I can return img from this method at the end
dispatch_semaphore_t sem = dispatch_semaphore_create(0);
[asset requestContentEditingInputWithOptions:coptions completionHandler:^(PHContentEditingInput *contentEditingInput, NSDictionary *info) {
NSURL* url = [contentEditingInput fullSizeImageURL];
int orientation = [contentEditingInput fullSizeImageOrientation];
CIImage* inputImage = [CIImage imageWithContentsOfURL:url options:nil];
inputImage = [inputImage imageByApplyingOrientation:orientation];
CIContext *context = [CIContext contextWithOptions:nil];
img = [UIImage imageWithCGImage:[context createCGImage:inputImage fromRect:inputImage.extent]];
dispatch_semaphore_signal(sem);
}];
dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER);
if (needToDoSomethingWithImg){
[self doSomethingWithImage:img];
}
return img;
}

Answer 1

Run this code through the static analyzer (shift+command+B or choose "Analyze" from the "Product" menu) and it will point out that createCGImage is creating a CGImageRef that you're never releasing.
You might want to do something like:
CGImageRef imageRef = [context createCGImage:inputImage fromRect:inputImage.extent];
img = [UIImage imageWithCGImage:imageRef];
CFRelease(imageRef);
By the way, you should not do this synchronously. You should do something like:
- (void) getRightlySizedImgFromAsset:(PHAsset*)asset completionHandler:(void (^)(UIImage *))completionHandler {
PHContentEditingInputRequestOptions *coptions = [PHContentEditingInputRequestOptions new];
coptions.canHandleAdjustmentData = ^BOOL(PHAdjustmentData *adjustmentData) { return NO; };
[asset requestContentEditingInputWithOptions:coptions completionHandler:^(PHContentEditingInput *contentEditingInput, NSDictionary *info) {
NSURL* url = [contentEditingInput fullSizeImageURL];
int orientation = [contentEditingInput fullSizeImageOrientation];
CIImage* inputImage = [CIImage imageWithContentsOfURL:url options:nil];
inputImage = [inputImage imageByApplyingOrientation:orientation];
CIContext *context = [CIContext contextWithOptions:nil];
CGImageRef imageRef = [context createCGImage:inputImage fromRect:inputImage.extent];
UIImage *image = [UIImage imageWithCGImage:imageRef];
CFRelease(imageRef);
// if this stuff needs to happen on main thread, then dispatch it to the main thread
if (needtodosomethingwithit)
[self doSomethingWithImage:image];
if (completionHandler) {
completionHandler(image);
}
}];
}

Answer 2

Rob is right on the money. And images can be big, so that's why you have a big leak. The rule of thumb with Core Foundation objects is the "create rule." Search in Xcode on "Create Rule" and read the article. The gist of it is this:
Core Foundation functions have names that indicate when you own a
returned object:
Object-creation functions that have “Create” embedded in the name;
Object-duplication functions that have “Copy” embedded in the name. If
you own an object, it is your responsibility to relinquish ownership
(using CFRelease) when you have finished with it.