Experimental async/await support

[kateinoigakukun]

import JavaScriptEventLoop
import JavaScriptKit

JavaScriptEventLoop.install()
let fetch = JSObject.global.fetch.function!.async

func printZen() async {
  let result = await try! fetch("https://api.github.com/zen").object!
  let text = await try! result.asyncing.text!()
  print(text)
}

JavaScriptEventLoop.runAsync {
  await printZen()
}

Current Issues

• Many C++ headers are copied from LLVM and Swift repository even though the runtime uses only a few interfaces.
• No tests
• Use of unsafe flag -enable-experimental-concurrency. If we remove it from Package.swift, users have to pass it from command line.

[github-actions]

Time Change: -843ms (9%) ✅

Total Time: 9,170.5ms

Test name	Duration	Change
Serialization/Swift Int to JavaScript	2,759.75ms	-455.25ms (16%)	👏
Serialization/Swift String to JavaScript	2,966ms	-284.75ms (9%)	✅

ℹ️ View Unchanged

Test name	Duration	Change
Serialization/Write JavaScript number directly	190.75ms	+1.25ms (0%)
Serialization/Write JavaScript string directly	198.5ms	+4.25ms (2%)
Object heap/Increment and decrement RC	3,055.5ms	-108.5ms (3%)

_{performance-action}

[MaxDesiatov]

Do I understand correctly that after this is merged we'll require our users to use dev toolchains and to compile with experimental concurrency enabled?

[MaxDesiatov]

Also, could we link with Swift runtime parts that are already included in the toolchain/SDK? Is a copy of it and LLVM stuff in our codebase required for this to work?

[kateinoigakukun]

Do I understand correctly that after this is merged we'll require our users to use dev toolchains and to compile with experimental concurrency enabled?

Yes, so I'm planning to merge this to next branch which will be used to use non-stable language features.

Also, could we link with Swift runtime parts that are already included in the toolchain/SDK? Is a copy of it and LLVM stuff in our codebase required for this to work?

JavaScriptEventLoop should be linked with libswiftCore.a and libswift_Concurrency.a to work. And LLVM headers are required for including swift/ABI/Task.h.

[MaxDesiatov]

Fair enough. I'm only worried that contents of these headers can change in a breaking way, especially given that concurrency stuff isn't ABI-stable yet, and maybe there's a better way to track them. A submodule is probably not practical due to the size of repositories that have these headers, so I don't have a better alternative to propose... Maybe some kind of scripts that pull latest versions of these headers automatically? 🤔

[kateinoigakukun]

Yes, so I wrote a shell script to fetch headers from swiftwasm/swift repository based on .swift-version snapshot.

https://github.com/swiftwasm/JavaScriptKit/blob/366d74e82e3aa40d604ac843743bb59b9412243b/Sources/_CJavaScriptEventLoop/README
https://github.com/swiftwasm/JavaScriptKit/blob/366d74e82e/Sources/_CJavaScriptEventLoop/scripts/copy-headers

[MaxDesiatov]

Seems legit then 👍