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How to use TryCatch properly?
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Stephan Beal  
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 More options Jul 20 2011, 10:27 pm
From: Stephan Beal <sgb...@googlemail.com>
Date: Thu, 21 Jul 2011 04:27:13 +0200
Local: Wed, Jul 20 2011 10:27 pm
Subject: How to use TryCatch properly?
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Hello, v8 gurus,

       v8::TryCatch tryCatch;
        tryCatch.SetVerbose(true);
        tryCatch.SetCaptureMessage(true);
        v8::ThrowException(v8::String::New("CATCH THIS, DAMMIT!"));
        assert( tryCatch.HasCaught() );
        assert( !tryCatch.Exception().IsEmpty() );

i can't for the life of me figure out how to use TryCatch properly. Both of
those assertions fail (well, whichever one is enabled fails).

What am i missing here?

:-?

--
----- stephan beal
http://wanderinghorse.net/home/stephan/


 
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Mads Sig Ager  
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 More options Jul 21 2011, 3:08 am
From: Mads Sig Ager <a...@chromium.org>
Date: Thu, 21 Jul 2011 09:08:11 +0200
Local: Thurs, Jul 21 2011 3:08 am
Subject: Re: [v8-users] How to use TryCatch properly?
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v8::ThrowException schedules an exception to be thrown when returning to
JavaScript. At the point where you ask if it has been caught it has not been
thrown yet.

Cheers,    -- Mads


 
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Stephan Beal  
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 More options Jul 21 2011, 3:11 am
From: Stephan Beal <sgb...@googlemail.com>
Date: Thu, 21 Jul 2011 09:11:31 +0200
Local: Thurs, Jul 21 2011 3:11 am
Subject: Re: [v8-users] How to use TryCatch properly?
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On Thu, Jul 21, 2011 at 9:08 AM, Mads Sig Ager <a...@chromium.org> wrote:

> v8::ThrowException schedules an exception to be thrown when returning to
> JavaScript. At the point where you ask if it has been caught it has not been
> thrown yet.

i see. Thank you for that clarification.

The return value of ThrowException(): is it Undefined() or an Empty handle?
i recall (perhaps incorrectly) reading both descriptions over the years.

--
----- stephan beal
http://wanderinghorse.net/home/stephan/


 
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Mads Sig Ager  
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 More options Jul 21 2011, 4:16 am
From: Mads Sig Ager <a...@chromium.org>
Date: Thu, 21 Jul 2011 10:16:43 +0200
Local: Thurs, Jul 21 2011 4:16 am
Subject: Re: [v8-users] How to use TryCatch properly?
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On Thu, Jul 21, 2011 at 9:11 AM, Stephan Beal <sgb...@googlemail.com> wrote:
> On Thu, Jul 21, 2011 at 9:08 AM, Mads Sig Ager <a...@chromium.org> wrote:

>> v8::ThrowException schedules an exception to be thrown when returning to
>> JavaScript. At the point where you ask if it has been caught it has not been
>> thrown yet.

> i see. Thank you for that clarification.

> The return value of ThrowException(): is it Undefined() or an Empty handle?
> i recall (perhaps incorrectly) reading both descriptions over the years.

It is undefined.

It *can* return an empty handle, but only if calling into V8 before it is
initialized or after it is dead (after an out of memory or similar).

Cheers,    -- Mads


 
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Stephan Beal  
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 More options Jul 21 2011, 4:21 am
From: Stephan Beal <sgb...@googlemail.com>
Date: Thu, 21 Jul 2011 10:21:06 +0200
Local: Thurs, Jul 21 2011 4:21 am
Subject: Re: [v8-users] How to use TryCatch properly?
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On Thu, Jul 21, 2011 at 9:08 AM, Mads Sig Ager <a...@chromium.org> wrote:

> v8::ThrowException schedules an exception to be thrown when returning to
> JavaScript. At the point where you ask if it has been caught it has not been
> thrown yet.

A slight clarification: does "returning to JS" mean returning to a higher
scope than the TryCatch, or calling back into v8 (perhaps in a deeper scope
than the TryCatch, where the TC is still alive)?

--
----- stephan beal
http://wanderinghorse.net/home/stephan/


 
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Mads Sig Ager  
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 More options Jul 21 2011, 4:36 am
From: Mads Sig Ager <a...@chromium.org>
Date: Thu, 21 Jul 2011 10:36:41 +0200
Local: Thurs, Jul 21 2011 4:36 am
Subject: Re: [v8-users] How to use TryCatch properly?
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On Thu, Jul 21, 2011 at 10:21 AM, Stephan Beal <sgb...@googlemail.com>wrote:

> On Thu, Jul 21, 2011 at 9:08 AM, Mads Sig Ager <a...@chromium.org> wrote:

>> v8::ThrowException schedules an exception to be thrown when returning to
>> JavaScript. At the point where you ask if it has been caught it has not been
>> thrown yet.

> A slight clarification: does "returning to JS" mean returning to a higher
> scope than the TryCatch, or calling back into v8 (perhaps in a deeper scope
> than the TryCatch, where the TC is still alive)?

It means actually returning to a JavaScript activation on the stack.
Returning to other C++ code will not throw the exception.

-- Mads


 
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Stephan Beal  
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 More options Jul 21 2011, 4:38 am
From: Stephan Beal <sgb...@googlemail.com>
Date: Thu, 21 Jul 2011 10:38:26 +0200
Local: Thurs, Jul 21 2011 4:38 am
Subject: Re: [v8-users] How to use TryCatch properly?
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On Thu, Jul 21, 2011 at 10:36 AM, Mads Sig Ager <a...@chromium.org> wrote:

> It means actually returning to a JavaScript activation on the stack.
> Returning to other C++ code will not throw the exception.

Okay, that explains my code's broken behaviour. Thank you :).

--
----- stephan beal
http://wanderinghorse.net/home/stephan/


 
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