Async/await syntax

[OCTAGRAM]

Hello!

With async/await we are finally (almost) able to write clean synchronous-style browser code. But Objective-J did not incorporate it in any way IIUC.

It is not an easy move, but what are the plans about it?

For instance, make all Objective-J methods implementations async, and all Objective-J method invocations await.

Or, like in ordinary JavaScript, move the burden of memorizing who's async, who's not, and forcing to write await by hand. But at least this is already something.

[cappbot]

Milestone: Someday. Label: #new. What's next? A reviewer should examine this issue.

[mrcarlberg]

Hello!

I guess this will be done in multiple steps for Objective-J. As it is a superset of Javascript we first need to support ECMAScript 2017. When that is done we can start incorporate it to the Objective-J language.

With that said, do you have any ideas or suggestions that you want in the language?

[OCTAGRAM]

For me would be easier to make everything async. But then quite many assumptions ruin. Handler may semi-execute when handling DOM event, and then next DOM event comes in between. But we cannot let handler fire. The environment becomes "multithreaded" otherwise.

I rely on Cappuccino to do the heavy lifting now, and the same way I would rely on Cappuccino to simulate "single main thread" while making all methods async. DOM elements must collect events or ignore them when "single main thread" is busy. That is, I guess, a serious architecture change.

In the short run I propose explicit async/await. Maybe @async before method. Maybe async before result type.

Third possible solution is based on making everything async, but instead of enabling long-running handlers, denying them to run long. DOM event handlers must enter scheduler, which is to replace window.setTimeout(…, 0);, and this scheduler runs Objective-J handler and expects completion. [CPThread sleepForTimeInterval:] maps to await new Promise, setTimeout, etc. for "non-main thread", but throws exception for "main thread" (bool global variable can be responsible for thinking we are in "main thread"). HTTP request throws exception (or, despite all recommendations, it executes synchronously). To start some long-running process Objective-J handler may use CPThread, which maps to adding jobs to scheduler.

So Objective-J event handler can launch several CPThreads, and all of them may possibly use long-running functions. Objective-J event handler "in the main thread" may possibly try to wait for their completion, and indeed all may end fast, thanks to the scheduler. But if not, if some threshold is passed or if scheduler is out of work (all threads "await" something that is not going to happen soon), Objective-J event handler is woken up with failure or exception.

This approach does not require big UI architecture changes.

[daboe01]

maybe we can/should integrate this with CPOperationQueue somehow?

[enquora]

Swift Evolution is now discussing async/await) including interoperability with Objective-C and its runtime (under Related Proposals).

Having a CPOperationQueue which didn't depend on the runloop would be particularly nice.

[mrcarlberg]

We have to keep things separate. I can at least find these topic in this interesting discussion:

1. Add async/await support in the Objective-J language. A good reference is the Swift Evolution link above.
2. The problem with the main thread that sometimes is heavily congested. My thinking here is to move everything in Cappuccino to a Web Worker (https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API). The only thing we will leave in the main thread is a DOMDisplayServer. To make DOM changes the Cappuccino framework (that is running in a Web Worker) will send the changes to the DOMDisplayServer (main thread).
3. Make CPOperationQueue work better. My thinking here is to allow CPOperationQueue to use a Web Worker to be able to run on their own.

With this said I think this issue should be about 1. Add async/await support in the Objective-J language. Feel free to open new issues for the other issues.

Really interesting topics

[daboe01]

-#new
+Objective-J

[cappbot]

Milestone: Someday. Label: Objective-J. What's next? A reviewer should examine this issue.

[daboe01]

@mrcarlberg is this still an issue?

[mrcarlberg]

Yes, I believe issue 1. above is fixed in the Node version when async/await syntax was added.

[daboe01]

@mrcarlberg i think we can close this one. as you said we can open new issues for the Web Worker stuff as needed. do you agree?