On Mon, Aug 28, 2017 at 16:10 Adam Kemp via swift-evolution < [email protected]> 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? 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 <[email protected]> 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 <[email protected]> > 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 <[email protected]> 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 < >> [email protected]> 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 <[email protected]> >>> 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 <[email protected]>, 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 <[email protected]> >>> 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 <[email protected]> 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 < >>>> [email protected]> 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 < >>>> [email protected]> 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 < >>>>> [email protected]>, 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 < >>>>> [email protected]> 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 <[email protected]> wrote: >>>>> >>>>>> >>>>>> On Aug 25, 2017, at 12:34 AM, Howard Lovatt <[email protected]> >>>>>> 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 >>>>> [email protected] >>>>> https://lists.swift.org/mailman/listinfo/swift-evolution >>>>> >>>>> -- >>>> -- Howard. >>>> >>>> _______________________________________________ >>>> swift-evolution mailing list >>>> [email protected] >>>> https://lists.swift.org/mailman/listinfo/swift-evolution >>>> >>>> >>> >>> _______________________________________________ >>> swift-evolution mailing list >>> [email protected] >>> https://lists.swift.org/mailman/listinfo/swift-evolution >>> >> >> > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution >
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