<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 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=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><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 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=""><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>If I understand correctly, In real code you are not supposed to call beginAsync.</div><div>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>Other library may provide entry point that run the code in a private thread pool.</div><div><br class=""></div><div>This is just a primitive used to support coroutine, but does not define how they are handled.</div><br class=""><div class=""><br class=""></div></body></html>