[swift-evolution] libdispatch renaming feedback

[Matt Wright]

> On Jun 15, 2016, at 11:14 AM, Guillaume Lessard via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Here’s some feedback after translating some Dispatch-heavy code for the new Dispatch module.
> 
> 1. I like the result. Thanks for the effort!
> 
> 2. Omissions
> 
> - Can't initialize a new queue or obtain a global queue using a DispatchQoS instance. [SR-1770]
> 
> One thing I have previously done was the following:
> 
> let anotherQueue: dispatch_queue_t = <somethingvalid>
> let matchedQueue = dispatch_get_global_queue(dispatch_queue_get_qos_class(anotherQueue, nil), 0)
> 
> There is no longer a way to do this.

Thanks for the feedback. I’ll take a look at getting something in that can do this.

> 
> Given that all the methods that enqueue blocks for execution have DispatchQoS parameters, this must be an oversight (I didn’t notice it when reviewing the proposal).
> 
> The following should exist:
> extension DispatchQueue {
>  init(qos: DispatchQoS, attributes: DispatchQueueAttributes)
>  class func global(qos: DispatchQoS, attributes: DispatchQueue.GlobalAttributes) -> DispatchQueue
> }
> extension DispatchQueueAttributes {
>  // replacing dispatch_queue_attr_make_with_qos_class:
>  init(qos: DispatchQoS, attributes: DispatchQueueAttributes)
> }
> 
> - DispatchTime should be Comparable [SR-1771]

I’m curious why you need to compare DispatchTime values but if you can do this via rawValue it seems like it should be Comparable, even if I can’t bring to mind an immediately useful use-case.

> - qos_class_self() and qos_class_main() do not translate to DispatchQoS [SR-1769]

SR-1769 has already been brought to my attention! I think that more or less covers all the comments you had about qos_class_t <-> DispatchQoS.

> 
> Since qos_class_t presumably isn’t disappearing (it’s used by Darwin pthreads), the following are needed:
> 
> extension DispatchQoS {
>  static func current() -> DispatchQoS // equivalent to qos_class_self()
>  static var main: DispatchQoS // equivalent to qos_class_main()
>  init(qos: qos_class_t) // perhaps with a relativePriority?
> }
> 
> 3. Oddities
> 
> - DispatchQueueAttributes is top-level, while DispatchQueue.GlobalAttributes is not.

I can’t immediately recall why I made this top-level but there was a technical problem with moving it into DispatchQueue. Perhaps that no longer exist, I’ll try again.

> 
> DispatchQueue.Attributes would look better to my eyes.
> 
> - Similarly, DispatchWorkItemFlags is top-level; it could perhaps be DispatchWorkItem.Flags
> 
> - QualityOfService and DispatchQoS.QoSClass seem redundant. One of these could probably go.
> (QualityOfService is defined under Foundation.NSObjCRuntime and is an enum with rawValue)

There are backwards compatibility issues with combining Foundation.QualityOfService and DispatchQoS.QoSClass. For now they need to remain separate.

> 
> 
> 4. Bad translations or fixits
> 
> - dispatch_get_global_queue(qos_class_self(), 0) gets an invalid suggestion (then again there is a void there, as noted above)
> 
> - dispatch_block_create does not have a fixit pointing to the new DispatchWorkItem type.
> 
> 
> Cheers,
> Guillaume Lessard
> 
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