@David, The signatures would be:
func processImage(_ image: Future<Image>) -> Future<Image> func translate(_ text: Future<String>) -> Future<Image> Inside `processImage` and `translate` you would `get` the values at the point were needed so that downloadImage and downloadText run in parallel (which is highly desirable). -- Howard. On 30 August 2017 at 07:21, David Hart <da...@hartbit.com> wrote: > I don’t think the examples are 100% equivalent. In your version with the > Future library, *preprocessImage* and *translate* need to accept futures > as argument, correct? That’s more restrictive than in my example code where > async/await specifically provide sugar over *then*. Plus I don’t > understand why you mention that the Future version handles errors when > async/await also plays very nicely with errors. > > On 29 Aug 2017, at 10:22, Howard Lovatt <howard.lov...@gmail.com> wrote: > > @David, > > Using the `Future` library based on GCD that I have previously posted your > example would be: > > let image = preprocessImage(downloadImage()) // These first two lines run in > parallellet text = translate(downloadText())render(image: image.get ?? > defaultImage, text: text.get ?? defaultText) > > > The main difference, and I would argue an improvement, is that the > `Future` version handles errors. > > So what advantage does async/await have over a `Future` library we can > write today? > > > -- Howard. > > On 29 August 2017 at 15:28, David Hart via swift-evolution < > swift-evolution@swift.org> wrote: > >> >> On 29 Aug 2017, at 02:22, Xiaodi Wu via swift-evolution < >> swift-evolution@swift.org> wrote: >> >> On Mon, Aug 28, 2017 at 16:10 Adam Kemp via swift-evolution < >> swift-evolution@swift.org> wrote: >> >>> I know what the proposal said. I’m making a case that there is value in >>> doing it differently. >>> >>> The composability of futures is valuable. Mixing and matching >>> async/await with futures is also valuable. The queue-returning behavior >>> that you can get from futures is also valuable, and building async/await on >>> top of futures means async/await can get that for free. >>> >> >> Why couldn't you mix and match async/await and futures and get the >> queue-return behavior of futures if futures are built on top of async/await >> instead off the other way around? >> >> >> We could, but the syntax is much worse. Contrast: >> >> *async/await built on top of Futures* >> >> let image = preprocessImage(downloadImage())let text = >> translate(downloadText()) >> await render(image: image, text: text) >> >> >> *Futures built on top of async/await* >> >> let image = Future(downloadImage).then({ preprocessImage($0) })let text = >> Future(downloadText).then({ translate($0) }) >> await render(image: image.get(), text: text.get()) >> >> >> Maybe you don’t value those things, which is fine. But I do, and maybe >>> other people do too. That’s why we’re having a discussion about it. >>> >>> It can also be valuable having a minimal implementation, but we have to >>> acknowledge that it comes with a downside as well. The problem with doing a >>> minimal implementation is that you can be stuck with the consequences for a >>> long time. I want to make sure that we’re not stuck with the consequences >>> of a minimal implementation that doesn’t adequately address the problems >>> that async/await should be addressing. I’d hate for Swift to get an >>> async/await that is so weak that it has to be augmented by tedious >>> boilerplate code before it’s useful. >>> >>> >>> On Aug 28, 2017, at 1:54 PM, Wallacy <walla...@gmail.com> wrote: >>> >>> We don't need to this now! >>> >>> Again: (Using proposal words) >>> >>> "It is important to understand that this is proposing compiler support >>> that is completely concurrency runtime-agnostic. This proposal does not >>> include a new runtime model (like "actors") - it works just as well with >>> GCD as with pthreads or another API. Furthermore, unlike designs in other >>> languages, it is independent of specific coordination mechanisms, such as >>> futures or channels, allowing these to be built as library feature" >>> >>> and >>> >>> "This proposal does not formally propose a Future type, or any other >>> coordination abstractions. There are many rational designs for futures, and >>> a lot of experience working with them. On the other hand, there are also >>> completely different coordination primitives that can be used with this >>> coroutine design, and incorporating them into this proposal only makes it >>> larger." >>> >>> and >>> >>> We focus on task-based concurrency abstractions commonly encountered in >>> client and server applications, particularly those that are highly event >>> driven (e.g. responding to UI events or requests from clients). This does >>> not attempt to be a comprehensive survey of all possible options, nor does >>> it attempt to solve all possible problems in the space of concurrency. >>> Instead, it outlines a single coherent design thread that can be built over >>> the span of years to incrementally drive Swift to further greatness. >>> >>> and >>> >>> This proposal has been kept intentionally minimal, but there are many >>> possible ways to expand this in the future. >>> >>> .... >>> >>> The point is: No Future type is indeed proposed yet! >>> >>> The proposal try to include de "minimum" required to implement a basic >>> async/await to solve the problem created by the GCD! (Pyramid of doom) >>> >>> The question is: How do you do the same using dispatch_async ? >>> dispatch_async also does not return nothing to do what you are intentend do >>> do! >>> >>> Algo, by Swift 5 manifesto, there's no compromise to make a "complete" >>> concurrency model by this time! >>> >>> My intention is only make parity to dispatch_async, but also make the >>> ground free to make more complex implementation like Futures in another >>> round on top of this one. >>> >>> This 'async T' can be a real type in the future? Maybe will... But >>> doesn't matter now! Now we only need to is some kind of type which need to >>> be unwrapped using await before use. Maybe this intermediary/virtual type >>> can be a real thing and gain some abilities at some point! Maybe a full >>> Future type, why not? >>> >>> Em seg, 28 de ago de 2017 às 17:33, Adam Kemp <adam.k...@apple.com> >>> escreveu: >>> >>>> How would these anonymous types get composed? If I wanted to implement >>>> a function that takes a collection of futures and wait on it, how would I >>>> do that? That is, how would I implement the equivalent of C#’s Task.WhenAll >>>> and Task.WhenAny methods? >>>> >>>> More generally, how do you pass one of these typeless futures to some >>>> other function so that we can do the waiting there? >>>> >>>> >>>> On Aug 28, 2017, at 1:23 PM, Wallacy <walla...@gmail.com> wrote: >>>> >>>> And that's why I (and others) are suggesting: >>>> >>>> func processImageData1a() async -> Image { >>>> let dataResource = async loadWebResource("dataprofile.txt") // No >>>> future type here... Just another way to call dispatch_async under the hood. >>>> let imageResource = async loadWebResource("imagedata.dat") >>>> >>>> // ... other stuff can go here to cover load latency... >>>> >>>> let imageTmp = await decodeImage(dataResource, imageResource) // >>>> Compiles force await call here... >>>> let imageResult = await dewarpAndCleanupImage(imageTmp) >>>> return imageResult >>>> } >>>> >>>> And now we gain all advantages of async/await again without to handle >>>> with one more type. >>>> >>>> Em seg, 28 de ago de 2017 às 17:07, Adam Kemp via swift-evolution < >>>> swift-evolution@swift.org> escreveu: >>>> >>>>> I think the biggest tradeoff is clearer when you look at the examples >>>>> from the proposal where futures are built on top of async/await: >>>>> >>>>> func processImageData1a() async -> Image { >>>>> let dataResource = Future { await loadWebResource("dataprofile.txt") >>>>> } >>>>> let imageResource = Future { await loadWebResource("imagedata.dat") >>>>> } >>>>> >>>>> // ... other stuff can go here to cover load latency... >>>>> >>>>> let imageTmp = await decodeImage(dataResource.get(), >>>>> imageResource.get()) >>>>> let imageResult = await dewarpAndCleanupImage(imageTmp) >>>>> return imageResult >>>>> } >>>>> >>>>> >>>>> With this approach you have to wrap each call site to create a future. >>>>> Compare to this: >>>>> >>>>> func processImageData1a() -> Future<Image> { >>>>> let dataResourceFuture = loadWebResource("dataprofile.txt”); >>>>> let imageResourceFuture = loadWebResource("imagedata.dat”); >>>>> >>>>> // ... other stuff can go here to cover load latency... >>>>> >>>>> let imageTmp = await decodeImage(await dataResourceFuture, await >>>>> imageResourceFuture) >>>>> let imageResult = await dewarpAndCleanupImage(imageTmp) >>>>> return imageResult >>>>> } >>>>> >>>>> >>>>> Here, not only are the explicit wrappers gone, but this function >>>>> itself can be used with either await or as a future. You get both options >>>>> with one implementation. >>>>> >>>>> As I’ve mentioned before, C#’s implementation is not tied to any one >>>>> particular futures implementation. The Task type is commonly used, but >>>>> async/await does not directly depend on Task. Instead it works with any >>>>> return type that meets certain requirements (detailed here: >>>>> https://blogs.msdn.microsoft.com/pfxteam/2011/01/13/await-anything/). >>>>> Swift could do this using a protocol, which can be retroactively applied >>>>> using an extension. >>>>> >>>>> Obviously for this to be useful we would need some kind of existing >>>>> future implementation, but at least we wouldn’t be tied to any particular >>>>> one. That would mean library maintainers who have already been using their >>>>> own futures implementations could quickly adopt async/await in their code >>>>> without having to rewrite their futures library or throw wrappers around >>>>> every usage of async/await. They could just adopt a protocol (using an >>>>> extension, even) and get async/await support for free. >>>>> >>>>> The downside is that this feature would be specific to the async/await >>>>> use case rather than a generic coroutine implementation (i.e., there would >>>>> have to be a separate compiler transform for yield return). It’s not clear >>>>> to me why it should be a goal to have just one generic coroutine feature. >>>>> The real-world usages of async/await and yield return are different enough >>>>> that I’m not convinced we could have a single compiler feature that meets >>>>> the needs of both cleanly. >>>>> >>>>> On Aug 27, 2017, at 7:35 PM, Florent Vilmart <flor...@flovilmart.com> >>>>> wrote: >>>>> >>>>> Adam, you’re completely right, languages as c# and JS have been >>>>> through the path before, (callback, Promises , async/await) I believe >>>>> Chris’s goal it to avoid building a promise implementation and go straight >>>>> to a coroutines model, which is more deeply integrated with the compiler. >>>>> I >>>>> don’t see a particular trade off, pursuing that route, and the main >>>>> benefit >>>>> is that coroutines can power any asynchronous metaphor (Signals, Streams, >>>>> Futures, Promises etc...) which is not true of Futures so i would tend to >>>>> think that for the long run, and to maximize usability, async/await/yield >>>>> would probably be the way to go. >>>>> >>>>> On Aug 27, 2017, 22:22 -0400, Adam Kemp <adam.k...@apple.com>, wrote: >>>>> >>>>> As has been explained, futures can be built on top of async/await (or >>>>> the other way around). You can have the best of both worlds. We are not >>>>> losing anything by having this feature. It would be a huge improvement to >>>>> have this as an option. >>>>> >>>>> However, using futures correctly requires more nested closures than >>>>> you have shown in your examples to avoid blocking any threads. That's why >>>>> you're not seeing the advantage to async/await. You're comparing examples >>>>> that have very different behaviors. >>>>> >>>>> That said, I have also expressed my opinion that it is better to build >>>>> async/await on top of futures rather than the other way around. I believe >>>>> it is more powerful and cleaner to make async/await work with any >>>>> arbitrary >>>>> future type (via a protocol). The alternative (building futures on top of >>>>> async/await) requires more code when the two are mixed. I very much prefer >>>>> how it's done in C#, where you can freely mix the two models without >>>>> having >>>>> to resort to ad-hoc wrappers, and you can use async/await with any futures >>>>> implementation you might already be using. >>>>> >>>>> I really think we should be having more discussion about the tradeoffs >>>>> between those two approaches, and I'm concerned that some of the opinions >>>>> about how C# does it are not based on a clear and accurate understanding >>>>> of >>>>> how it actually works in that language. >>>>> >>>>> -- >>>>> Adam Kemp >>>>> >>>>> On Aug 27, 2017, at 6:02 PM, Howard Lovatt <howard.lov...@gmail.com> >>>>> wrote: >>>>> >>>>> The async/await is very similar to the proposed Future (as I posed >>>>> earlier) with regard to completion-handler code, they both re-write the >>>>> imported completion-handler function using a closure, the relevant >>>>> sentence >>>>> from the Async Proposal is: >>>>> >>>>> "Under the hood, the compiler rewrites this code using nested closures >>>>> ..." >>>>> >>>>> >>>>> Unlike the proposed future code the async code is not naturally >>>>> parallel, in the running example the following lines from the async code >>>>> are run in series, i.e. await blocks: >>>>> >>>>> let dataResource = await loadWebResource("dataprofile.txt") >>>>> let imageResource = await loadWebResource("imagedata.dat") >>>>> >>>>> The equivalent lines using the proposed Future: >>>>> >>>>> let dataResource = loadWebResource("dataprofile.txt") >>>>> let imageResource = loadWebResource("imagedata.dat") >>>>> >>>>> Run in parallel and therefore are potentially faster assuming that >>>>> resources, like cores and IO, are available. >>>>> >>>>> Therefore you would be better using a Future than an async, so why >>>>> provide an async unless you can make a convincing argument that it allows >>>>> you to write a better future? >>>>> >>>>> -- Howard. >>>>> >>>>> On 28 August 2017 at 09:59, Adam Kemp <adam.k...@apple.com> wrote: >>>>> >>>>>> This example still has nested closures (to create a Future), and >>>>>> still relies on a synchronous get method that will block a thread. >>>>>> Async/await does not require blocking any threads. >>>>>> >>>>>> I’m definitely a fan of futures, but this example isn’t even a good >>>>>> example of using futures. If you’re using a synchronous get method then >>>>>> you’re not using futures properly. They’re supposed to make it easy to >>>>>> avoid writing blocking code. This example just does the blocking call on >>>>>> some other thread. >>>>>> >>>>>> Doing it properly would show the benefits of async/await because it >>>>>> would require more nesting and more complex error handling. By >>>>>> simplifying >>>>>> the code you’ve made a comparison between proper asynchronous code (with >>>>>> async/await) and improper asynchronous code (your example). >>>>>> >>>>>> That tendency to want to just block a thread to make it easier is >>>>>> exactly why async/await is so valuable. You get simple code while still >>>>>> doing it correctly. >>>>>> >>>>>> -- >>>>>> Adam Kemp >>>>>> >>>>>> On Aug 27, 2017, at 4:00 PM, Howard Lovatt via swift-evolution < >>>>>> swift-evolution@swift.org> wrote: >>>>>> >>>>>> The running example used in the white paper coded using a Future is: >>>>>> >>>>>> func processImageData1() -> Future<Image> { >>>>>> return AsynchronousFuture { _ -> Image in >>>>>> let dataResource = loadWebResource("dataprofile.txt") // >>>>>> dataResource and imageResource run in parallel. >>>>>> let imageResource = loadWebResource("imagedata.dat") >>>>>> let imageTmp = decodeImage(dataResource.get ?? >>>>>> Resource(path: "Default data resource or prompt user"), imageResource.get >>>>>> ?? Resource(path: "Default image resource or prompt user")) >>>>>> let imageResult = dewarpAndCleanupImage(imageTmp.get ?? >>>>>> Image(dataPath: "Default image or prompt user", imagePath: "Default image >>>>>> or prompt user")) >>>>>> return imageResult.get ?? Image(dataPath: "Default image or >>>>>> prompt user", imagePath: "Default image or prompt user") >>>>>> } >>>>>> } >>>>>> >>>>>> This also avoids the pyramid of doom; the pyramid is avoided by >>>>>> converting continuation-handlers into either a sync or future, i.e. it is >>>>>> the importer that eliminates the nesting by translating the code >>>>>> automatically. >>>>>> >>>>>> This example using Future also demonstrates three advantages of >>>>>> Future: they are naturally parallel (dataResource and imageResource lines >>>>>> run in parallel), they timeout automatically (get returns nil if the >>>>>> Future >>>>>> has taken too long), and if there is a failure (for any reason including >>>>>> timeout) it provides a method of either detecting the failure or >>>>>> providing >>>>>> a default (get returns nil on failure). >>>>>> >>>>>> There are a three of other advantages a Future has that this example >>>>>> doesn’t show: control over which thread the Future runs on, Futures can >>>>>> be >>>>>> cancelled, and debugging information is available. >>>>>> >>>>>> You could imagine `async` as a syntax sugar for Future, e.g. the >>>>>> above Future example could be: >>>>>> >>>>>> func processImageData1() async -> Image { >>>>>> let dataResource = loadWebResource("dataprofile.txt") // >>>>>> dataResource and imageResource run in parallel. >>>>>> let imageResource = loadWebResource("imagedata.dat") >>>>>> let imageTmp = decodeImage(dataResource.get ?? >>>>>> Resource(path: "Default data resource or prompt user"), imageResource.get >>>>>> ?? Resource(path: "Default image resource or prompt user")) >>>>>> let imageResult = dewarpAndCleanupImage(imageTmp.get ?? >>>>>> Image(dataPath: "Default image or prompt user", imagePath: "Default image >>>>>> or prompt user")) >>>>>> return imageResult.get ?? Image(dataPath: "Default image or >>>>>> prompt user", imagePath: "Default image or prompt user") >>>>>> } >>>>>> >>>>>> Since an async is sugar for Future the async runs as soon as it is >>>>>> created (as soon as the underlying Future is created) and get returns an >>>>>> optional (also cancel and status would be still be present). Then if you >>>>>> want control over threads and timeout they could be arguments to async: >>>>>> >>>>>> func processImageData1() async(queue: DispatchQueue.main, timeout: >>>>>> .seconds(5)) -> Image { ... } >>>>>> >>>>>> On Sat, 26 Aug 2017 at 11:00 pm, Florent Vilmart < >>>>>> flor...@flovilmart.com> wrote: >>>>>> >>>>>>> Howard, with async / await, the code is flat and you don’t have to >>>>>>> unowned/weak self to prevent hideous cycles in the callbacks. >>>>>>> Futures can’t do that >>>>>>> >>>>>>> On Aug 26, 2017, 04:37 -0400, Goffredo Marocchi via swift-evolution < >>>>>>> swift-evolution@swift.org>, wrote: >>>>>>> >>>>>>> With both he now built in promises in Node8 as well as libraries >>>>>>> like Bluebird there was ample time to evaluate them and convert/auto >>>>>>> convert at times libraries that loved callback pyramids of doom when the >>>>>>> flow grows complex into promise based chains. Converting to Promises >>>>>>> seems >>>>>>> magical for the simple case, but can quickly descend in hard to follow >>>>>>> flows and hard to debug errors when you move to non trivial multi path >>>>>>> scenarios. JS is now solving it with their implementation of >>>>>>> async/await, >>>>>>> but the point is that without the full picture any single solution would >>>>>>> break horribly in real life scenarios. >>>>>>> >>>>>>> Sent from my iPhone >>>>>>> >>>>>>> On 26 Aug 2017, at 06:27, Howard Lovatt via swift-evolution < >>>>>>> swift-evolution@swift.org> wrote: >>>>>>> >>>>>>> My argument goes like this: >>>>>>> >>>>>>> 1. You don't need async/await to write a powerful future type; you >>>>>>> can use the underlying threads just as well, i.e. future with >>>>>>> async/await >>>>>>> is no better than future without. >>>>>>> >>>>>>> 2. Since future is more powerful, thread control, cancel, and >>>>>>> timeout, people should be encouraged to use this; instead because >>>>>>> async/await are language features they will be presumed, incorrectly, >>>>>>> to be >>>>>>> the best way, consequently people will get into trouble with deadlocks >>>>>>> because they don't have control. >>>>>>> >>>>>>> 3. async/await will require some engineering work and will at best >>>>>>> make a mild syntax improvement and at worst lead to deadlocks, therefore >>>>>>> they just don't carry their weight in terms of useful additions to >>>>>>> Swift. >>>>>>> >>>>>>> Therefore, save some engineering effort and just provide a future >>>>>>> library. >>>>>>> >>>>>>> To turn the question round another way, in two forms: >>>>>>> >>>>>>> 1. What can async/wait do that a future can't? >>>>>>> >>>>>>> 2. How will future be improved if async/await is added? >>>>>>> >>>>>>> >>>>>>> -- Howard. >>>>>>> >>>>>>> On 26 August 2017 at 02:23, Joe Groff <jgr...@apple.com> wrote: >>>>>>> >>>>>>>> >>>>>>>> On Aug 25, 2017, at 12:34 AM, Howard Lovatt < >>>>>>>> howard.lov...@gmail.com> wrote: >>>>>>>> >>>>>>>> In particular a future that is cancellable is more powerful that >>>>>>>> the proposed async/await. >>>>>>>> >>>>>>>> >>>>>>>> It's not more powerful; the features are to some degree disjoint. >>>>>>>> You can build a Future abstraction and then use async/await to sugar >>>>>>>> code >>>>>>>> that threads computation through futures. Getting back to Jakob's >>>>>>>> example, >>>>>>>> someone (maybe the Clang importer, maybe Apple's framework developers >>>>>>>> in an >>>>>>>> overlay) will still need to build infrastructure on top of IBActions >>>>>>>> and >>>>>>>> other currently ad-hoc signalling mechanisms to integrate them into a >>>>>>>> more >>>>>>>> expressive coordination framework. >>>>>>>> >>>>>>>> -Joe >>>>>>>> >>>>>>> >>>>>>> _______________________________________________ >>>>>>> swift-evolution mailing list >>>>>>> swift-evolution@swift.org >>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution >>>>>>> >>>>>>> -- >>>>>> -- Howard. >>>>>> >>>>>> _______________________________________________ >>>>>> swift-evolution mailing list >>>>>> swift-evolution@swift.org >>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution >>>>>> >>>>>> >>>>> >>>>> _______________________________________________ >>>>> swift-evolution mailing list >>>>> swift-evolution@swift.org >>>>> https://lists.swift.org/mailman/listinfo/swift-evolution >>>>> >>>> >>>> >>> _______________________________________________ >>> swift-evolution mailing list >>> swift-evolution@swift.org >>> https://lists.swift.org/mailman/listinfo/swift-evolution >>> >> _______________________________________________ >> swift-evolution mailing list >> swift-evolution@swift.org >> https://lists.swift.org/mailman/listinfo/swift-evolution >> >> >> >> _______________________________________________ >> swift-evolution mailing list >> swift-evolution@swift.org >> https://lists.swift.org/mailman/listinfo/swift-evolution >> >> > >
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