<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">Le 25 sept. 2017 à 18:54, Trevör Anne Denise via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><blockquote type="cite" class=""><div class=""><br class="Apple-interchange-newline">Le 25 sept. 2017 à 13:33, Trevör ANNE DENISE <<a href="mailto:trevor.annedenise@icloud.com" class="">trevor.annedenise@icloud.com</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><div dir="auto" class=""><br class=""><div class="">Le 25 sept. 2017 à 11:55, Thomas <<a href="mailto:tclementdev@free.fr" class="">tclementdev@free.fr</a>> a écrit :<br class=""><br class=""></div><blockquote type="cite" class=""><div class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On 25 Sep 2017, at 10:23, Trevör Anne Denise via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><br class=""><div class=""><blockquote type="cite" class=""><div class="">Le 24 sept. 2017 à 12:00, Jean-Daniel <<a href="mailto:mailing@xenonium.com" class="">mailing@xenonium.com</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class="Apple-interchange-newline"><br class=""><blockquote type="cite" class=""><div class="">Le 23 sept. 2017 à 12:23, Trevör Anne Denise via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><br class=""><div class=""><blockquote type="cite" class=""><div class="">Le 20 sept. 2017 à 21:15, Jean-Daniel <<a href="mailto:mailing@xenonium.com" class="">mailing@xenonium.com</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class="Apple-interchange-newline"><br class=""><blockquote type="cite" class=""><div class="">Le 20 sept. 2017 à 08:36, Trevör Anne Denise via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div class=""><blockquote type="cite" class=""><div class=""><br class="">Le 18 sept. 2017 à 18:07, Pierre Habouzit <<a href="mailto:pierre@habouzit.net" class="">pierre@habouzit.net</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class="Apple-interchange-newline">-Pierre</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""><blockquote type="cite" class=""><div class="">On Sep 18, 2017, at 2:04 AM, Trevör Anne Denise <<a href="mailto:trevor.annedenise@icloud.com" class="">trevor.annedenise@icloud.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><blockquote type="cite" class="" style="font-family: SFMono-Light; font-size: 11px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class=""><br class="Apple-interchange-newline">Le 18 sept. 2017 à 07:57, Pierre Habouzit <<a href="mailto:pierre@habouzit.net" class="">pierre@habouzit.net</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><blockquote type="cite" class=""><div class="">On Sep 17, 2017, at 3:52 AM, Trevör ANNE DENISE via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">Hello everyone,<br class=""><br class="">I have a few questions about async await in Swift.<br class=""><br class="">Say that you have :<br class=""><br class="">func foo() async {<br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>print("Hey")<br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>await bar()<br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>print("How are you ?")<br class="">}<br class=""><br class="">First of all, am I right to say that :<br class="">1) If the bar function wasn't an async function, the thread would be blocked until bar returns, at this point print("How are you ?") would be executed and its only after that that the function calling foo() would get back "control"<br class=""></div></div></blockquote><div class=""><br class=""></div><div class="">I don't think you can quite call await without marking foo() as async (?).</div></div></div></blockquote><div class="" style="font-family: SFMono-Light; font-size: 11px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: SFMono-Light; font-size: 11px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: SFMono-Light; font-size: 11px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">Yes, that's what I meant, case one would call foo() without await if it wasn't async.</div><div class="" style="font-family: SFMono-Light; font-size: 11px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><br class="" style="font-family: SFMono-Light; font-size: 11px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><blockquote type="cite" class="" style="font-family: SFMono-Light; font-size: 11px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class=""><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""><blockquote type="cite" class=""><div class=""><div class="">2) Here (with async bar function), if bar() takes some time to execute,</div></div></blockquote><div class=""><br class=""></div><div class="">Not quite, `await bar()` is afaict syntactic sugar for:</div><div class=""><br class=""></div></div><blockquote class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; margin: 0px 0px 0px 40px; border: none; padding: 0px;"><div class=""><div class="">bar {</div></div><div class=""><div class=""> printf("How are you ?");</div></div><div class=""><div class="">}</div></div></blockquote><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">Where bar used to take a closure before, the compiler is just making it for you. bar itself will be marked async and will handle its asynchronous nature e.g. using dispatch or something else entirely.</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">This has nothing to do with "time".</div></div></blockquote><div class="" style="font-family: SFMono-Light; font-size: 11px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: SFMono-Light; font-size: 11px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: SFMono-Light; font-size: 11px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">If it's just syntactic sugar then how does this solve this issue mentioned in the concurrency manifesto ?</div><div class="" style="font-family: SFMono-Light; font-size: 11px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">"Beyond being syntactically inconvenient, completion handlers are problematic because their syntax suggests that they will be called on the current queue, but that is not always the case. For example, one of the top recommendations on Stack Overflow is to implement your own custom async operations with code like this (Objective-C syntax):"</div></div></blockquote><div class=""><br class=""></div><div class="">"where" things run is not addressed by async/await afaict, but Actors or any library-level usage of it.</div><br class=""></div></div></blockquote><br class=""></div><div class=""><br class=""></div><div class="">So since async await don't have any impact on where things are executed, what would happen concretely with this code ?</div><div class=""><br class=""></div><div class="">func slowFunction(_ input: [Int]) async -> [Int] {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>var results = [Int]()</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>for element in input {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>results += [someLongComputation(with: element)]</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>}</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>return results</div><div class="">}</div><div class=""><br class=""></div><div class="">beginAsync {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>await slowFunction(manyElements)</div><div class="">}</div><div class=""><br class=""></div><div class="">I didn't specified anything about which queue/thread runs this code, so what would happen ? Would beginAsync block until slowFunction completes ?</div><div class=""><br class=""></div></div></div></blockquote><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">If I understand correctly, In real code you are not supposed to call beginAsync.</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">It should be wrapped by high level frameworks. GCD may provide a method that take an async lambda as parameter and dispatch it on a the global concurrent queue.</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">Other library may provide entry point that run the code in a private thread pool.</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">This is just a primitive used to support coroutine, but does not define how they are handled.</div></div></blockquote><br class=""></div><div class=""><br class=""></div><div class="">Thank you everyone, I understand it better now, I still have some questions tough.</div><div class="">Just to be sure that I am understanding this correctly, if you some async function and it suspends itself, then your current async function making this call will also suspend itself, right ?</div><div class=""><br class=""></div><div class="">Also, I understand how suspendAsync will be used to warp current callback based functions into async/await friendly functions and in this case :</div><div class=""><pre class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, "Liberation Mono", Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; word-wrap: normal; padding: 16px; overflow: auto; line-height: 1.45; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal; color: rgb(36, 41, 46);"><span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(111, 66, 193);">getStuff</span>() async <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">-></span> Stuff {
<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">return</span> await suspendAsync { continuation <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">in</span>
<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">getStuff</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">completion</span>: continuation)
}
}</pre><div class=""><br class=""></div><div class="">Here, I understand how the function controls where continuation is executed, but how would you write an API supporting async/await from scratch ?</div><div class=""><br class=""></div><div class="">Say that I want to build an async function that downloads data, with libdispatch I could do :</div><div class="">func dowloadSomething() {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>await someBackgroundQueue.asyncCorountine()</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>// Here I would put my code for downloading data</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span></div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>// But would I have to put anything after that to choose where to execute the continuation ? DispatchQueue.main.syncCorountine() maybe ?</div><div class="">}</div></div></div></div></blockquote><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">The high level stuff is not designed yet, and how to specify the continuation target queue/thread is not defined at this point.</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">Your code will probably be something like</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">Dispatch.startAync {</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><span class="Apple-tab-span" style="white-space: pre;"> </span>val stuff = await downloadStuff()</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><span class="Apple-tab-span" style="white-space: pre;"> </span>// do something with stuff once it is done.</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">}</div></div></blockquote></div><br class=""><div class=""><br class=""></div><div class="">Do you mean that the API to execute the continuation back on its original thread ? (avoiding shared mutable state)</div></div></div></blockquote><br class=""></div><div class="">I think you have to do something like this:</div><div class=""><br class=""></div><div class="">func async doSomethingInBackground(callbackQueue: DispatchQueue) -> SomeResult {<br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>await someBackgroundQueue.asyncCorountine()</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span><br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>// Here I would put my (potentially lengthy) background code.<br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span><br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>// Jump on the requested callback queue.</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>await callbackQueue.asyncCoroutine()</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span></div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>// Return result (if any).</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>return result</div><div class="">}</div><div class=""><br class=""></div><div class=""><br class=""></div>Thomas<div class=""><br class=""></div></div></blockquote><br class=""><div class="">I hope this will be handled automatically the compiler tough !</div></div></div></blockquote></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">Did anyone started to sketch a design for how giving back control to the calling queue will work ?</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">Would it make any sense to limit asyncCorountine() to the scope of the function where it gets called and implicitly "hop back" to the calling queue so that no shared mutable state issues arise ?</div></div></blockquote><div><br class=""></div><div>No. Async methods are not require to be dispatched on a queue and all threads are not required to have a queue.</div></div><br class=""><div class=""><br class=""></div></body></html>