[webkit-dev] JSC framework API proposal: setting a handler for enqueuing tasks

[Maciej Stachowiak]

> On Jul 7, 2015, at 3:36 AM, Yusuke SUZUKI <utatane.tea at gmail.com> wrote:
> 
> On Tue, Jul 7, 2015 at 8:54 AM, Geoffrey Garen <ggaren at apple.com <mailto:ggaren at apple.com>> wrote:
> I’m suggesting a default runloop for non-web content.
> 
> I haven’t read through the details of integrating with the web content definition of micro task.
> 
> Geoff
> 
> OK. Reinventing runloop each time is costly.
> On the other hand, sometimes, users would like to use the other runloop such as libuv.
> So what do you think about providing the both.
> 
> 1. Provide default runloop in JSC
> 2. Provide the way to register callback for enqueueJob. If it's provided, (1) is disabled for this VM.
> 
> (1) would become the following (quick proposal)
> 
> void JSContextRunMicrotasks(JSContextRef, unsigned someFlags);
> bool JSContextIsMicrotasksEmpty(JSContextRef);
> 
> In this case, if we would like to close the VM,
> 
> bool executed = false;
> do {
>     executed = false;
>     for each context belongging to the given VM {
>         if (JSContxtIsMicrotasksEmpty(context)) {
>             executed = true;
>             JSContextRunMicrotasks(context, ...);
>         }
>     }
> } while (executed);
> Close(VM);

I think that Goeff's suggest would be that microtasks would normally run without the client having to make any special calls at all to account for them. Possibly this may imply a requirement of running a CFRunLoop on the relevant thread.

I also think your API doesn't account for nesting very well - it requires the client app to know the VM nesting level. It would be better if that was tracked and micro tasks could run on exiting the outermost VM and/or 

> 
> (2) would become the original proposal.
>  
> 
>> On Jul 6, 2015, at 4:44 PM, Maciej Stachowiak <mjs at apple.com <mailto:mjs at apple.com>> wrote:
>> 
>> 
>> Should JS be defining an event loop abstraction that WebCore then uses? That would be weird, because the required behavior of the even loop in web content is chock full of issues that are not at all related to JavaScript. JSC doesn't even know enough to run microtasks at all the right times (from reading the spec it seems that way, at least) for the Web case. Or are you saying it would have a fallback runloop for non-Web contents?
>> 
>> Regards,
>> Maciej
>> 
>>> On Jul 6, 2015, at 3:24 PM, Geoffrey Garen <ggaren at apple.com <mailto:ggaren at apple.com>> wrote:
>>> 
>>> I think it would be better for JavaScriptCore to handle micro tasks natively.
>>> 
>>> It’s not so great for each client to need to reinvent the microtask runloop abstraction.
>>> 
>>> Geoff
>>> 
>>>> On Jul 6, 2015, at 10:05 AM, Yusuke SUZUKI <utatane.tea at gmail.com <mailto:utatane.tea at gmail.com>> wrote:
>>>> 
>>>> Hi WebKittens,
>>>> 
>>>> I've landed the update of the ES6 Promise implementation.
>>>> Through this work, I've experimentally added the internal private function, @enqueueJob(JS function, JS array for arguments).
>>>> This is corresponding to the ES6 spec EnqueueJob[1].
>>>> 
>>>> This EnqueueJob handler is now tightly integrated with WebCore's microtask infrastructure. So in JSC framework side, we cannot use this function.
>>>> As a result, current JSC framework disables Promise because there's no event loop abstraction.
>>>> 
>>>> So I propose the API configuring euqueueJob handler into JSC VM (That corresponds to the Realm in ECMA spec).
>>>> 
>>>> Like,
>>>> 
>>>> void JSContextGroupSetEnqueueJobCallback(JSContextGroupRef, JSEnqueueJobCallback, void* callbackData);
>>>> 
>>>> What do you think about this?
>>>> 
>>>> [1]: http://ecma-international.org/ecma-262/6.0/#sec-enqueuejob <http://ecma-international.org/ecma-262/6.0/#sec-enqueuejob>
>>>> 
>>>> Best Regards,
>>>> Yusuke Suzuki
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>>> 
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>> 
> 
> 

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