Re: Uncatchable exceptions

On 5/2/16 9:13 PM, Ehsan Akhgari wrote:
> I'm trying to figure out how to implement this function.  AFAICT the
> implementation is roughly as follows:
>
> bool JS_IsUncatchableExceptionPending(JSContext* cx) {
>    return cx->didSomeJSNativeReturnFalse() ||
>           cx->isThrowingOutOfMemory();
> }
>
> It is the didSomeJSNativeReturnFalse() that I don't know how to
> implement.  As far as I can understand stuff that happens in js::Call()
> et al, there isn't even a flag indicating such case. :(  It seems like
> all that happens here is we return false and pass the ball to the
> caller, which itself returns false and so on.

That's correct.  That is exactly how things work right now.

I think there are basically two options here:

1)  We change the places that return false without setting pending 
exceptions to make some explicit call to an API we add.  The problem is 
finding them all.  :(  That said, it's not clear to me that SpiderMonkey 
itself ever has this behavior.  Gecko does, for the slow script dialog 
and worker termination, but all of that happens outside SpiderMonkey... 
  Presumably you need to implement a "throw uncatchable exception" API 
anyway, right?

2)  We restrict the use of JS_IsUncatchableExceptionPending to the 
situation when false is known to have been returned.  In that case it 
just becomes !cx->hasPendingException().

-Boris