Re: [v8-users] Re: Can you Set the CurrentIsolate

[Ian Bull]

THANK-YOU! Honestly, thank-you! I've been looking at this all week and this 
message had me look at the code in a slightly different way.

I knew this about Exit() / Enter() and I actually don't use these. I just 
create Scopes, and they do the Entering / Exiting for me. And (for the most 
part) the scopes are Stack based, so when they go out of (C++) scope, 
things get cleaned up properly. However, your message had me re-visit this, 
and I realized that I actually create one heap based Scope when an Isolate 
is created, and delete it when the Isolate is removed. This is fine, and 
fits the pattern, but it does mean that if you Create and Destroy two 
isolates, but don't nest them, then you haven't matched each Enter() with 
an Exit().

There was no reason to create this heap based Scope.

Thanks again!

Cheers,
Ian

On Friday, 28 July 2017 13:25:10 UTC-7, Jakob Kummerow wrote:
>
> On Fri, Jul 28, 2017 at 12:36 PM, Ian Bull  > wrote:
>
>> The problem with Enter() is that if you're already Entered, now you're in 
>> there twice. So if it's a patchwork solution that checks if the MyIsolate 
>> != Isolate::GetCurrent, and then calls MyIsolate->Enter(), I could started 
>> entering an unknown number of times (I may already be entered, just not the 
>> "current one"). This blows up later on when you try to Dispose() the 
>> isolate. Of course I could track the number of times I performed this 
>> patchwork solution, and before Dispose is called, I could call Exit() that 
>> number of times, but now were really getting hacky. 
>>
>> I was hoping for an easy way to tell V8 that "this isolate" is the 
>> current, without any side effects.
>>
>
> Enter() and Exit() are the way to do this. They should always show up in 
> pairs, and then no "patchwork solution" should be necessary. E.g. if your 
> callback Enter()s another Isolate, it should afterwards Exit() from that 
> Isolate again, which will restore the previous state. In other words, 
> consider the following sequence:
>
> Isolate* A ...;
>
> A->Enter();
> // A == Isolate::GetCurrent()
> ...
> Isolate* B ...;
> B->Enter();
> // B == Isolate::GetCurrent()
> ...
> B->Exit();
> // A == Isolate::GetCurrent(), no second call to A->Enter() is necessary
>
>  
>
>>
>> On Fri, 28 Jul 2017 at 12:28 Zac Hansen  
>> wrote:
>>
>>> This is just a guess, but does v8::Isolate::Enter do it?
>>>
>>>
>>> https://v8.paulfryzel.com/docs/master/classv8_1_1_isolate.html#aec80bb49b6b7647ff75e8f2cc9484ea3
>>>
>>>
>>>
>>> On Friday, July 28, 2017 at 11:56:16 AM UTC-7, Ian Bull wrote:

 I know Isolate::GetCurrent is deprecated, but it's still being used 
 inside V8 itself in places, and there are times when it's getting the 
 wrong 
 isolate. [1] for example.

 [1] String::Value::Value(v8::Local obj) : str_(NULL), 
 length_(0)  // in api.cc

 I created Isolate A, and inside a callback, I create some new Isolates, 
 Lock and Unlock. Then when I return from the callback, the 
 Isolate::GetCurrent no longer points to Isolate A, and in some cases 
 points 
 to null. I am always tracking which Isolate I'm using, and it's pretty 
 easy 
 to detect that the wrong "current isolate" is set. Is there a way to tell 
 V8 that Isolate::GetCurrent should now point to a particular Isolate?

 Cheers,
 Ian

>>> -- 
>>
>>
>

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Re: [v8-users] Re: Can you Set the CurrentIsolate

[Jakob Kummerow]

On Fri, Jul 28, 2017 at 12:36 PM, Ian Bull  wrote:

> The problem with Enter() is that if you're already Entered, now you're in
> there twice. So if it's a patchwork solution that checks if the MyIsolate
> != Isolate::GetCurrent, and then calls MyIsolate->Enter(), I could started
> entering an unknown number of times (I may already be entered, just not the
> "current one"). This blows up later on when you try to Dispose() the
> isolate. Of course I could track the number of times I performed this
> patchwork solution, and before Dispose is called, I could call Exit() that
> number of times, but now were really getting hacky.
>
> I was hoping for an easy way to tell V8 that "this isolate" is the
> current, without any side effects.
>

Enter() and Exit() are the way to do this. They should always show up in
pairs, and then no "patchwork solution" should be necessary. E.g. if your
callback Enter()s another Isolate, it should afterwards Exit() from that
Isolate again, which will restore the previous state. In other words,
consider the following sequence:

Isolate* A ...;

A->Enter();
// A == Isolate::GetCurrent()
...
Isolate* B ...;
B->Enter();
// B == Isolate::GetCurrent()
...
B->Exit();
// A == Isolate::GetCurrent(), no second call to A->Enter() is necessary



>
> On Fri, 28 Jul 2017 at 12:28 Zac Hansen  wrote:
>
>> This is just a guess, but does v8::Isolate::Enter do it?
>>
>> https://v8.paulfryzel.com/docs/master/classv8_1_1_isolate.html#
>> aec80bb49b6b7647ff75e8f2cc9484ea3
>>
>>
>>
>> On Friday, July 28, 2017 at 11:56:16 AM UTC-7, Ian Bull wrote:
>>>
>>> I know Isolate::GetCurrent is deprecated, but it's still being used
>>> inside V8 itself in places, and there are times when it's getting the wrong
>>> isolate. [1] for example.
>>>
>>> [1] String::Value::Value(v8::Local obj) : str_(NULL),
>>> length_(0)  // in api.cc
>>>
>>> I created Isolate A, and inside a callback, I create some new Isolates,
>>> Lock and Unlock. Then when I return from the callback, the
>>> Isolate::GetCurrent no longer points to Isolate A, and in some cases points
>>> to null. I am always tracking which Isolate I'm using, and it's pretty easy
>>> to detect that the wrong "current isolate" is set. Is there a way to tell
>>> V8 that Isolate::GetCurrent should now point to a particular Isolate?
>>>
>>> Cheers,
>>> Ian
>>>
>> --
>
>

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Re: [v8-users] Re: Can you Set the CurrentIsolate

[Ian Bull]

The problem with Enter() is that if you're already Entered, now you're in
there twice. So if it's a patchwork solution that checks if the MyIsolate
!= Isolate::GetCurrent, and then calls MyIsolate->Enter(), I could started
entering an unknown number of times (I may already be entered, just not the
"current one"). This blows up later on when you try to Dispose() the
isolate. Of course I could track the number of times I performed this
patchwork solution, and before Dispose is called, I could call Exit() that
number of times, but now were really getting hacky.

I was hoping for an easy way to tell V8 that "this isolate" is the current,
without any side effects.

On Fri, 28 Jul 2017 at 12:28 Zac Hansen  wrote:

> This is just a guess, but does v8::Isolate::Enter do it?
>
>
> https://v8.paulfryzel.com/docs/master/classv8_1_1_isolate.html#aec80bb49b6b7647ff75e8f2cc9484ea3
>
>
>
> On Friday, July 28, 2017 at 11:56:16 AM UTC-7, Ian Bull wrote:
>>
>> I know Isolate::GetCurrent is deprecated, but it's still being used
>> inside V8 itself in places, and there are times when it's getting the wrong
>> isolate. [1] for example.
>>
>> [1] String::Value::Value(v8::Local obj) : str_(NULL),
>> length_(0)  // in api.cc
>>
>> I created Isolate A, and inside a callback, I create some new Isolates,
>> Lock and Unlock. Then when I return from the callback, the
>> Isolate::GetCurrent no longer points to Isolate A, and in some cases points
>> to null. I am always tracking which Isolate I'm using, and it's pretty easy
>> to detect that the wrong "current isolate" is set. Is there a way to tell
>> V8 that Isolate::GetCurrent should now point to a particular Isolate?
>>
>> Cheers,
>> Ian
>>
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[v8-users] Re: Can you Set the CurrentIsolate

[Zac Hansen]

This is just a guess, but does v8::Isolate::Enter do it?

https://v8.paulfryzel.com/docs/master/classv8_1_1_isolate.html#aec80bb49b6b7647ff75e8f2cc9484ea3



On Friday, July 28, 2017 at 11:56:16 AM UTC-7, Ian Bull wrote:
>
> I know Isolate::GetCurrent is deprecated, but it's still being used inside 
> V8 itself in places, and there are times when it's getting the wrong 
> isolate. [1] for example.
>
> [1] String::Value::Value(v8::Local obj) : str_(NULL), 
> length_(0)  // in api.cc
>
> I created Isolate A, and inside a callback, I create some new Isolates, 
> Lock and Unlock. Then when I return from the callback, the 
> Isolate::GetCurrent no longer points to Isolate A, and in some cases points 
> to null. I am always tracking which Isolate I'm using, and it's pretty easy 
> to detect that the wrong "current isolate" is set. Is there a way to tell 
> V8 that Isolate::GetCurrent should now point to a particular Isolate?
>
> Cheers,
> Ian
>

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[v8-users] Can you Set the CurrentIsolate

[Ian Bull]

I know Isolate::GetCurrent is deprecated, but it's still being used inside 
V8 itself in places, and there are times when it's getting the wrong 
isolate. [1] for example.

[1] String::Value::Value(v8::Local obj) : str_(NULL), length_(0) 
 // in api.cc

I created Isolate A, and inside a callback, I create some new Isolates, 
Lock and Unlock. Then when I return from the callback, the 
Isolate::GetCurrent no longer points to Isolate A, and in some cases points 
to null. I am always tracking which Isolate I'm using, and it's pretty easy 
to detect that the wrong "current isolate" is set. Is there a way to tell 
V8 that Isolate::GetCurrent should now point to a particular Isolate?

Cheers,
Ian

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