KingfisherManager retrieveImage completionHandler not called on specified queue

[fgulan]

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Issue Description

What

After upgrading from 4.x to 5.x this snippet of code:

KingfisherManager.shared.retrieveImage(with: url, options: [.callbackQueue(.mainAsync)]) { result in
    // invoked on background thread
}

doesn't respect .callbackQueue option and callback is executed on some background thread. Callback is called (background thread) from:

KingfisherManager.retrieveImageFromCache(source:options:completionHandler:) at KingfisherManager.swift:324

Currently I don't have time for further debug, but I suspect on method:

ImageCache.retrieveImage(forKey:options:callbackQueue:completionHandler:) at ImageCache.swift:440

since there is a default parameter for callbackQueue which is .untouch and options are not parsed at all.

Reproduce

Currently I've managed to reproduce this issue only when image is loaded form disk cache. For downloading image and in memory cache it seems that it works fine.

[onevcat]

Yes, you are 100% right on this.

The default value of .untouch in ImageCache gives a chance to "overwrite" the default .mainCurrentOrAsync in options (since there should be no need to dispatch to the main queue). It is a performance trick but I forgot to use the callback queue at an upper level. I will give it a fix now.

[onevcat]

Currently I've managed to reproduce this issue only when image is loaded form disk cache. For downloading image and in memory cache it seems that it works fine.

I guess loading from memory cache would also cause this problem...

[aksswami]

I am also facing this issue after migrating to 5.0. As a workaround for now, I have switched to main thread in completion handler.

Btw @onevcat thanks for the v5, It improved a lot of things and resolved couple of pressing issues.

[rocxteady]

I am using version 5.3.1. I face the same problem. Any progress on this? My code looks like this:

    let options: KingfisherOptionsInfo = [.callbackQueue(.mainAsync)]
        ImageCache.default.retrieveImage(forKey: key, options: options, completionHandler: { (result) in
            switch result {
            case .success(let value):
                
            case .failure(let error):
               
            }
        })

Thanks.

[onevcat]

@rocxteady Hi, this method is a bit different for internal performance reason. You need to specify the callback queue explicitly, otherwise, it uses .untouch to avoid unnecessary dispatch.

ImageCache.default.retrieveImage(
    forKey: key, options: options, callbackQueue: .mainAsync, completionHandler: { /* */  }
)

[rocxteady]

@onevcat thank you for the information. But it's a bit misleasing. I thought we could set a callback queue. Maybe you should change it we can't set it this way. Therefore there will not be any misleading. Thank you again.