Use Dispatch Work Items | raywenderlich.com

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This is a companion discussion topic for the original entry at https://www.raywenderlich.com/9461083-ios-concurrency-with-gcd-and-operations/lessons/4
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Hey Audrey! Thank you for the tutorial.
I have a question here.
Why did we use quality of service as ‘utility’ for the global DispatchQueue to download the image? Could we have also used ‘userInitiated’ here? Would it make a big difference if we use one or the other? Thanks.

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hi Shruti! userInitiated is for tasks that run in response to an actual action by the user, like tapping a button. In the Concurrency app, the download tasks just populate the collection view, so it’s more of a background activity.

userInitiated for all the image downloads would probably use more battery power than utility

Note: This question is about Episode 5.

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Thanks Audrey. So we don’t use background qos in that case because it is a time sensitive high priority task which the user is aware of and not any background task like database management, synchronizing, and backups.

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hi Shruti: yes, background is for tasks that don’t really affect the user experience.

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I totally did not understand the point of:

dispatchPrecondition(condition: .onQueue(DispatchQueue.main))

In the playground, we are already on the main queue… so what does this actually do?

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hi Jason! it’s just to show you this useful method exists and how it works. It was new in Swift 4.