For anyone following along, I've submitted a PR to fix this as
https://github.com/apple/swift/pull/3923.
-Kevin
On Mon, Aug 1, 2016, at 03:04 PM, Kevin Ballard wrote:
> Hmm. The implementation of DispatchQueue.async(execute: DispatchWorkItem) is
> as follows:
>
> public func async(execute workItem: DispatchWorkItem) {
> // _swift_dispatch_async preserves the @convention(block)
> // for work item blocks.
> _swift_dispatch_async(self, workItem._block)
> }
>
> This comment indicates that someone was already aware of the problem and
> fixed it in some places but not all. This also suggests that the problem
> itself can be fixed merely by replacing the remaining uses of
> __dispatch_async with _swift_dispatch_async(). I will try this out.
>
> -Kevin
>
> On Mon, Aug 1, 2016, at 02:53 PM, Kevin Ballard via swift-dev wrote:
> > I just filed SR-2246 about how `queue.async(flags: .barrier)` is completely
> > broken, and I think the problem comes down to `dispatch_block_t` is being
> > imported as `() -> ()` instead of as `@convention(block) () -> ()`, and
> > therefore `__dispatch_async` has the type `(DispatchQueue, () -> Void) ->
> > Void` instead of `(DispatchQueue, @convention(block) () -> Void) -> Void`.
> >
> > The reason I'm sending this email is because I'd like to fix this, but I
> > have no idea how. In Swift 2.x the SDK overlay had an explicit definition
> > for `dispatch_block_t` instead of importing it from the C header, but with
> > the new Dispatch API, it seems to be relying on the clang importer to get
> > __dispatch_async and friends (though I'm not sure what causes the __ prefix
> > since dispatch_async doesn't seem to have the relevant attribute). Swift
> > 2.2 had a typealias for dispatch_block_t, but Swift 3 marks
> > dispatch_block_t as being unavailable (although again I don't know how
> > since I don't see the relevant attribute in the macOS SDK), so presumably
> > reintroducing a typealias isn't a good idea, if it even works at all.
> >
> > -Kevin Ballard
> > _______________________________________________
> > swift-dev mailing list
> > [email protected]
> > https://lists.swift.org/mailman/listinfo/swift-dev
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