> On Feb 23, 2017, at 8:35 AM, Karl Wagner via swift-corelibs-dev
> <swift-corelibs-dev@swift.org> wrote:
>
> Would it be possible to make a cancelable version of
> DispatchQueue.concurrentPerform, allowing you to abort any
> yet-to-be-scheduled blocks?
>
> The use-case is for when you’re concurrently performing a job and one of them
> sets a flag or fails in a way which already defines the result. Further
> execution wouldn’t affect the outcome, so it would be nice if an operation
> could flag back to concurrentPerform that it doesn’t have to schedule any
> more jobs.
>
> For a real-world example, see this concurrent RandomAccessCollection wrapper
> I was building: https://gist.github.com/karwa/43ae838809cc68d317003f2885c71572
Your example is:
var _error: Error?
DispatchQueue.concurrentPerform(iterations: numericCast(count)) {
do { try body($0) }
catch { _error = error } // TODO: lock. Would be cool if we could cancel
future iterations, too...
}
if let error = _error {
try rescue(error)
}
So how would cancelability be superior to saying this?
var _error: Error?
DispatchQueue.concurrentPerform(iterations: numericCast(count)) {
guard _error == nil else { return }
do { try body($0) }
catch { _error = error } // TODO: lock. Would be cool if we could cancel
future iterations, too...
}
if let error = _error {
try rescue(error)
}
--
Brent Royal-Gordon
Architechies
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