Promise resolver and promise result #76

rogchap · 2021-02-11T10:32:36Z

Enables the (basic) Promise API. eg:

iso, _ := v8go.NewIsolate()
global, _ := v8go.NewObjectTemplate(iso)

fetchfn, _ := v8go.NewFunctionTemplate(iso, func(info *v8go.FunctionCallbackInfo) *v8go.Value {
	args := info.Args()
	url := args[0].String()
	resolver, _ := v8go.NewPromiseResolver(info.Context())

	go func() {
		res, _ := http.Get(url)
		body, _ := ioutil.ReadAll(res.Body)
		val, _ := v8go.NewValue(iso, string(body))
		resolver.Resolve(val)
	}()
	return resolver.GetPromise().Value
})
global.Set("fetch", fetchfn, v8go.ReadOnly)

ctx, _ := v8go.NewContext(iso, global)
val, _ := ctx.RunScript("fetch('https://rogchap.com/v8go')", "")
prom, _ := val.AsPromise()

// wait for the promise to resolve
for prom.State() == v8go.Pending {
	continue
}
fmt.Printf("%s\n", strings.Split(prom.Result().String(), "\n")[0])
// Output:
// <!DOCTYPE html>

resolves #69

codecov · 2021-02-11T10:33:39Z

Codecov Report

Merging #76 (d233d29) into master (9848a00) will increase coverage by 0.57%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #76      +/-   ##
==========================================
+ Coverage   94.07%   94.64%   +0.57%     
==========================================
  Files          10       11       +1     
  Lines         388      411      +23     
==========================================
+ Hits          365      389      +24     
+ Misses         16       15       -1     
  Partials        7        7

Impacted Files	Coverage Δ
promise.go	`100.00% <100.00%> (ø)`
value.go	`95.09% <100.00%> (+0.09%)`	⬆️
function_template.go	`100.00% <0.00%> (+4.34%)`	⬆️

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kuoruan · 2021-02-22T07:18:38Z

Dose exception.go required when reject a promise?
Can I just reject a string?

e, _ := v8go.NewValue(iso, "any errors")
resolver.Reject(e)

rogchap · 2021-02-22T07:22:39Z

You should be able to reject with any "Value" which includes a string, but it's most common to use an Error/Exception

rogchap · 2021-02-23T22:39:00Z

Just a quick update:

Sorry for taking so long in getting this PR finished; it's almost done.

Annoyingly, I'm in the process of moving house, so packing boxes has been taking most of my spare time 😞

Should be fully moved in by this time next week, and should be able to continue my work on v8go.

jensneuse · 2021-03-02T07:33:49Z

I'm not experienced with v8 but like to ask a question.
Looking at this code:

for prom.State() == v8go.Pending {
	continue
}

It seems, this is constantly calling the cgo bridge, doesn't it?
Will this affect runtime performance?
Would it make sense to blocking read on a channel until the v8 calls a resolved/rejected callback?

rogchap · 2021-03-02T11:04:44Z

@jensneuse Thanks for the suggestion. Hopefully this helps answer your questions:

It seems, this is constantly calling the cgo bridge, doesn't it?

It does 😓

Will this affect runtime performance?

Not really. The main issues around performance arise from transferring large amounts of data between C and Go and having to copy that data into memory on the Go side to make sure it does not get freed on the C side before you use it on the Go side. This func is returning an enum aka integer by value so you shouldn't notice any overhead in doing this in Go over doing the same thing in C++.

Would it make sense to blocking read on a channel until the v8 calls a resolved/rejected callback?

It's a nice idea, but one of the goals of the project is stay as close to the V8 API as possible; it also has a lot larger overhead as callbacks are not an easy thing to manage between Go and C (Have a look at the FunctionTemplate code to get an idea of the complexity)

rogchap · 2021-03-02T11:10:02Z

I'm having a hard time with getting Error Exceptions working. This simple line is causing a segfault:

Exception::Error(String::Empty(iso));

I've verified that the Isolate* is valid as I can create other values, just not Exception value. 🤷‍♂️

It's not critical for this PR to have the Exception/Error objects, but I thought it would be nice for the Promise rejections.
As noted above, you can use any Value as the value to the Reject function.

I'm tempted to exclude the exception.go stuff (just make it private for now) and revisit in another PR.

tmc · 2021-03-03T03:58:03Z

I'm tempted to exclude the exception.go stuff (just make it private for now) and revisit in another PR.

It seems like that can come in a follow-on commit.

tmc

LGTM, some small comments.

tmc · 2021-03-03T04:07:23Z

promise.go

+// The associated Promise will be in a Pending state.
+func NewPromiseResolver(ctx *Context) (*PromiseResolver, error) {
+	if ctx == nil {
+		return nil, errors.New("v8go: Context is required")


nite: lowercase?

kuoruan · 2021-03-03T07:05:53Z

Hi @rogchap
V8 v8.9 now in stable channel.
https://omahaproxy.appspot.com/ shows the version is 8.9.255.20

It supports top level await. https://v8.dev/blog/v8-release-89#top-level-await

Could you please update the V8 binary file version?

rogchap · 2021-03-03T08:45:49Z

@kuoruan Top level await only works at the top level of a module not at the top top level; which is a bit miss leading.

It's still behind a feature flag but I'll look to see if we can add it and upgrade v8 to the latest stable version.

I'll do this in a seperate PR

kuoruan · 2021-03-28T03:55:48Z

promise.go

+}
+
+// Reject
+func (r *PromiseResolver) Reject(err *Value) bool {


Why not change this to Valuer?
So that we can reject an object here

lebronyang1 · 2023-11-01T06:37:25Z

for prom.State() == v8go.Pending {
continue
}

@rogchap Hi, I don't always wait for promise results, Are there more effective ways to resolve this problem?
Wether I can allows the isolate execute other context, when wait promise results? In other words, How do I use the isolate in multiple threads? Especially promise, I think it's so slowly.

Promise resolver and promise result

3e4da54

rogchap added 2 commits February 19, 2021 14:29

Merge branch 'master' into promise

136ea34

update persistent value to match master

9675c5e

Add docs, test and Exception types

bccfa1d

rogchap added 2 commits March 2, 2021 22:21

remove the exception error functions

649ed14

add test for when value is not a promise

1944a6e

rogchap requested review from tmc and zwang March 2, 2021 11:32

rogchap marked this pull request as ready for review March 2, 2021 11:32

tmc approved these changes Mar 3, 2021

View reviewed changes

zwang approved these changes Mar 3, 2021

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update changelog

d233d29

rogchap merged commit 794781e into master Mar 7, 2021

rogchap deleted the promise branch March 7, 2021 23:50

rogchap mentioned this pull request Mar 8, 2021

Function Templates with callback functions in Go #68

Merged

This was referenced Mar 18, 2021

Add Isolate.ThrowException(exception) support #90

Closed

Allow setting/unsetting of V8 feature flags #96

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kuoruan reviewed Mar 28, 2021

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jmattheis mentioned this pull request Feb 22, 2022

Question about thread safety #290

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Promise resolver and promise result #76

Promise resolver and promise result #76

rogchap commented Feb 11, 2021

codecov bot commented Feb 11, 2021 •

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kuoruan commented Feb 22, 2021

rogchap commented Feb 22, 2021

rogchap commented Feb 23, 2021

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rogchap commented Mar 2, 2021

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tmc commented Mar 3, 2021

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tmc Mar 3, 2021

kuoruan commented Mar 3, 2021

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kuoruan Mar 28, 2021

lebronyang1 commented Nov 1, 2023

Promise resolver and promise result #76

Promise resolver and promise result #76

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