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Where are the exception-objects allocated?

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  Where are the exception-objects allocated? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-13 17:59 +0100
    Re: Where are the exception-objects allocated? Öö Tiib <ootiib@hot.ee> - 2019-11-13 10:10 -0800
      Re: Where are the exception-objects allocated? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-13 19:14 +0100
        Re: Where are the exception-objects allocated? Öö Tiib <ootiib@hot.ee> - 2019-11-13 10:24 -0800
          Re: Where are the exception-objects allocated? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-13 19:27 +0100
            Re: Where are the exception-objects allocated? Öö Tiib <ootiib@hot.ee> - 2019-11-13 10:40 -0800
              Re: Where are the exception-objects allocated? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-13 19:44 +0100
                Re: Where are the exception-objects allocated? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-11-13 21:58 -0800
    Re: Where are the exception-objects allocated? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-13 10:18 -0800
      Re: Where are the exception-objects allocated? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-13 19:28 +0100
        Re: Where are the exception-objects allocated? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-13 10:44 -0800
          Re: Where are the exception-objects allocated? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-13 19:46 +0100
            Re: Where are the exception-objects allocated? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-13 20:06 +0100
            Re: Where are the exception-objects allocated? Öö Tiib <ootiib@hot.ee> - 2019-11-13 11:36 -0800
          Re: Where are the exception-objects allocated? scott@slp53.sl.home (Scott Lurndal) - 2019-11-13 19:41 +0000
            Re: Where are the exception-objects allocated? Ian Collins <ian-news@hotmail.com> - 2019-11-14 20:11 +1300
    Re: Where are the exception-objects allocated? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-11-14 12:42 +0100
      Re: Where are the exception-objects allocated? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-14 13:07 +0100

#70108 — Where are the exception-objects allocated?

Can anyone tell me what would be a proper way to allocate storage
for an exception-object being thrown without causing that this
allocation might fail? And remember that these objects even have
to live longer than a thread because you might refer to it by
an std::exception_ptr.

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#70109

On Wednesday, 13 November 2019 18:59:58 UTC+2, Bonita Montero  wrote:
> Can anyone tell me what would be a proper way to allocate storage
> for an exception-object being thrown without causing that this
> allocation might fail? And remember that these objects even have
> to live longer than a thread because you might refer to it by
> an std::exception_ptr.

Does not matter. Implementation makes copy of it as temporary
object in unspecified storage during throw expression.
Implementation destroys it when last exception_ptr to
it is destroyed or when catch clause that caught it is left
without rethrow ... whatever happens last.

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#70110

> On Wednesday, 13 November 2019 18:59:58 UTC+2, Bonita Montero  wrote:
>> Can anyone tell me what would be a proper way to allocate storage
>> for an exception-object being thrown without causing that this
>> allocation might fail? And remember that these objects even have
>> to live longer than a thread because you might refer to it by
>> an std::exception_ptr.

> Does not matter. ...

It does matter because it is interesting and no one seems to know it.

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#70112

On Wednesday, 13 November 2019 20:15:05 UTC+2, Bonita Montero  wrote:
> > On Wednesday, 13 November 2019 18:59:58 UTC+2, Bonita Montero  wrote:
> >> Can anyone tell me what would be a proper way to allocate storage
> >> for an exception-object being thrown without causing that this
> >> allocation might fail? And remember that these objects even have
> >> to live longer than a thread because you might refer to it by
> >> an std::exception_ptr.
> 
> > Does not matter. ...
> 
> It does matter because it is interesting and no one seems to know it.


I answered precisely why and you snipped it and then claimed that
I did not know it? :D You can not allocate these objects,
Implementation does it into unspecified storage.

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#70113

>>> On Wednesday, 13 November 2019 18:59:58 UTC+2, Bonita Montero  wrote:
>>>> Can anyone tell me what would be a proper way to allocate storage
>>>> for an exception-object being thrown without causing that this
>>>> allocation might fail? And remember that these objects even have
>>>> to live longer than a thread because you might refer to it by
>>>> an std::exception_ptr.

>>> Does not matter. ...

>> It does matter because it is interesting and no one seems to know it.

> I answered precisely ...

"unspecified storage" isn't a precise answer.

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#70115

On Wednesday, 13 November 2019 20:27:47 UTC+2, Bonita Montero  wrote:
> >>> On Wednesday, 13 November 2019 18:59:58 UTC+2, Bonita Montero  wrote:
> >>>> Can anyone tell me what would be a proper way to allocate storage
> >>>> for an exception-object being thrown without causing that this
> >>>> allocation might fail? And remember that these objects even have
> >>>> to live longer than a thread because you might refer to it by
> >>>> an std::exception_ptr.
> 
> >>> Does not matter. ...
> 
> >> It does matter because it is interesting and no one seems to know it.
> 
> > I answered precisely ...
> 
> "unspecified storage" isn't a precise answer.

It is precise answer to question asked. If you want to know something
that you did not ask then sorry, I'm no psychiatist.

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#70116

>>>>> On Wednesday, 13 November 2019 18:59:58 UTC+2, Bonita Montero  wrote:
>>>>>> Can anyone tell me what would be a proper way to allocate storage
>>>>>> for an exception-object being thrown without causing that this
>>>>>> allocation might fail? And remember that these objects even have
>>>>>> to live longer than a thread because you might refer to it by
>>>>>> an std::exception_ptr.

>>>>> Does not matter. ...

>>>> It does matter because it is interesting and no one seems to know it.

>>> I answered precisely ...

>> "unspecified storage" isn't a precise answer.

> It is precise answer to question asked. ...

"unspecified" isn't precise.

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#70124

On 11/13/2019 10:44 AM, Bonita Montero wrote:
>>>>>> On Wednesday, 13 November 2019 18:59:58 UTC+2, Bonita Montero  wrote:
>>>>>>> Can anyone tell me what would be a proper way to allocate storage
>>>>>>> for an exception-object being thrown without causing that this
>>>>>>> allocation might fail? And remember that these objects even have
>>>>>>> to live longer than a thread because you might refer to it by
>>>>>>> an std::exception_ptr.
> 
>>>>>> Does not matter. ...
> 
>>>>> It does matter because it is interesting and no one seems to know it.
> 
>>>> I answered precisely ...
> 
>>> "unspecified storage" isn't a precise answer.
> 
>> It is precise answer to question asked. ...
> 
> "unspecified" isn't precise.
> 

Are you JG?

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#70111

On Wednesday, November 13, 2019 at 11:59:58 AM UTC-5, Bonita Montero wrote:
> Can anyone tell me what would be a proper way to allocate storage
> for an exception-object being thrown without causing that this
> allocation might fail? And remember that these objects even have
> to live longer than a thread because you might refer to it by
> an std::exception_ptr.

Exception objects are not created by user code; they are temporary
objects created by the implementation, copy-initialized by the
expression passed to the throw expression. It is unspecified how the
implementation allocates the storage that they are stored in. The
relevant wording of the standard is:
123456789012345678901234567890123456789012345678901234567890123456789012
"3 Throwing an exception copy-initializes (11.6, 15.8) a temporary
object, called the exception object. An lvalue denoting the temporary is
used to initialize the variable declared in the matching handler (18.3).
If the type of the exception object would be an incomplete type or a
pointer to an incomplete type other than cv void the program is ill-
formed.
4 The memory for the exception object is allocated in an unspecified
way, except as noted in 6.7.4.1." (18.1).

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#70114

>> Can anyone tell me what would be a proper way to allocate storage
>> for an exception-object being thrown without causing that this
>> allocation might fail? And remember that these objects even have
>> to live longer than a thread because you might refer to it by
>> an std::exception_ptr.

> Exception objects are not created by user code; they are temporary
> objects created by the implementation, copy-initialized by the
> expression passed to the throw expression. It is unspecified how the
> implementation allocates the storage that they are stored in. ...

I know that this is unspecified.
But I'm interested how this is actually implemented.

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#70117

On Wednesday, November 13, 2019 at 1:28:54 PM UTC-5, Bonita Montero wrote:
> >> Can anyone tell me what would be a proper way to allocate storage
> >> for an exception-object being thrown without causing that this
> >> allocation might fail? And remember that these objects even have
> >> to live longer than a thread because you might refer to it by
> >> an std::exception_ptr.
> 
> > Exception objects are not created by user code; they are temporary
> > objects created by the implementation, copy-initialized by the
> > expression passed to the throw expression. It is unspecified how the
> > implementation allocates the storage that they are stored in. ...
> 
> I know that this is unspecified.
> But I'm interested how this is actually implemented.

Then you need to be specific about which implementations you're most interested in. For best results, you should ask in forums that are specific to those implementations. Those kinds of details are not widely known, because ordinary developers have no need to know them, so the people who do know such details are far easier to find in such specialized forums, rather than in this one.

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#70118

>>>> Can anyone tell me what would be a proper way to allocate storage
>>>> for an exception-object being thrown without causing that this
>>>> allocation might fail? And remember that these objects even have
>>>> to live longer than a thread because you might refer to it by
>>>> an std::exception_ptr.

>>> Exception objects are not created by user code; they are temporary
>>> objects created by the implementation, copy-initialized by the
>>> expression passed to the throw expression. It is unspecified how the
>>> implementation allocates the storage that they are stored in. ...

>> I know that this is unspecified.
>> But I'm interested how this is actually implemented.

> Then you need to be specific about which implementations you're most interested in. For best results, you should ask in forums that are specific to those implementations. Those kinds of details are not widely known, because ordinary developers have no need to know them, so the people who do know such details are far easier to find in such specialized forums, rather than in this one.

I'm not interested in some particular implementation but in feasible
implementations. I thought someone here would be so creative as to
have some adequate ideas.

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#70119

> I'm not interested in some particular implementation but in feasible
> implementations. I thought someone here would be so creative as to
> have some adequate ideas.

I just found this (https://libcxxabi.llvm.org/spec.html):

| void* __cxa_allocate_exception(size_t thrown_size) throw();
| Effects: Allocates memory to hold the exception to be thrown.
| thrown_size is the size of the exception object. Can allocate
| additional memory to hold private data. If memory can not be
| allocated, call std::terminate().
| Returns: A pointer to the memory allocated for the exception object.

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#70120

On Wednesday, 13 November 2019 20:46:58 UTC+2, Bonita Montero  wrote:
> >>>> Can anyone tell me what would be a proper way to allocate storage
> >>>> for an exception-object being thrown without causing that this
> >>>> allocation might fail? And remember that these objects even have
> >>>> to live longer than a thread because you might refer to it by
> >>>> an std::exception_ptr.
> 
> >>> Exception objects are not created by user code; they are temporary
> >>> objects created by the implementation, copy-initialized by the
> >>> expression passed to the throw expression. It is unspecified how the
> >>> implementation allocates the storage that they are stored in. ...
> 
> >> I know that this is unspecified.
> >> But I'm interested how this is actually implemented.
> 
> > Then you need to be specific about which implementations you're most interested in. For best results, you should ask in forums that are specific to those implementations. Those kinds of details are not widely known, because ordinary developers have no need to know them, so the people who do know such details are far easier to find in such specialized forums, rather than in this one.
> 
> I'm not interested in some particular implementation but in feasible
> implementations. I thought someone here would be so creative as to
> have some adequate ideas.

Huh? Each implementation does something feasible. IIRC then gcc 
version where I looked in tried first to malloc and if that failed
then tried to use emergency buffer that it had reserved for desperate
times and if that was used up then called std::terminate.

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#70121

James Kuyper <jameskuyper@alumni.caltech.edu> writes:
>On Wednesday, November 13, 2019 at 1:28:54 PM UTC-5, Bonita Montero wrote:
>> >> Can anyone tell me what would be a proper way to allocate storage
>> >> for an exception-object being thrown without causing that this
>> >> allocation might fail? And remember that these objects even have
>> >> to live longer than a thread because you might refer to it by
>> >> an std::exception_ptr.
>>=20
>> > Exception objects are not created by user code; they are temporary
>> > objects created by the implementation, copy-initialized by the
>> > expression passed to the throw expression. It is unspecified how the
>> > implementation allocates the storage that they are stored in. ...
>>=20
>> I know that this is unspecified.
>> But I'm interested how this is actually implemented.
>
>Then you need to be specific about which implementations you're most intere=
>sted in. For best results, you should ask in forums that are specific to th=
>ose implementations. Those kinds of details are not widely known, because o=
>rdinary developers have no need to know them, so the people who do know suc=
>h details are far easier to find in such specialized forums, rather than in=
> this one.

Or BM could simply download the compiler sources and figure it out.

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#70131

On 14/11/2019 08:41, Scott Lurndal wrote:
> James Kuyper <jameskuyper@alumni.caltech.edu> writes:
>> On Wednesday, November 13, 2019 at 1:28:54 PM UTC-5, Bonita Montero wrote:
>>>>> Can anyone tell me what would be a proper way to allocate storage
>>>>> for an exception-object being thrown without causing that this
>>>>> allocation might fail? And remember that these objects even have
>>>>> to live longer than a thread because you might refer to it by
>>>>> an std::exception_ptr.
>>> =20
>>>> Exception objects are not created by user code; they are temporary
>>>> objects created by the implementation, copy-initialized by the
>>>> expression passed to the throw expression. It is unspecified how the
>>>> implementation allocates the storage that they are stored in. ...
>>> =20
>>> I know that this is unspecified.
>>> But I'm interested how this is actually implemented.
>>
>> Then you need to be specific about which implementations you're most intere=
>> sted in. For best results, you should ask in forums that are specific to th=
>> ose implementations. Those kinds of details are not widely known, because o=
>> rdinary developers have no need to know them, so the people who do know suc=
>> h details are far easier to find in such specialized forums, rather than in=
>> this one.
> 
> Or BM could simply download the compiler sources and figure it out.

Rude trolls don't do that..

-- 
Ian.

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#70136

On 13.11.2019 17:59, Bonita Montero wrote:
> Can anyone tell me what would be a proper way to allocate storage
> for an exception-object being thrown without causing that this
> allocation might fail? And remember that these objects even have
> to live longer than a thread because you might refer to it by
> an std::exception_ptr.

For string data you can leverage the internal special immutable string 
class by using `std::runtime_error` or a derived class.

It can of course throw when the original exception is created, but after 
that it's guaranteed that copying does not throw:

C++17 §21.8.2/2:
“Each standard library class T that derives from class exception shall 
have a publicly accessible copy constructor and a publicly accessible 
copy assignment operator that do not exit with an exception.”

For other data you have to ensure this guarantee yourself.

A reasonable approach is to minimize the amount of other data in an 
exception.


- Alf

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#70137

> C++17 §21.8.2/2:
> “Each standard library class T that derives from class exception shall 
> have a publicly accessible copy constructor and a publicly accessible 
> copy assignment operator that do not exit with an exception.”

1. I'm talking about the storage for the exception-object itself;
    this isn't allocated by your own code but the rundime-library.
2. I just posted my parallel merge-sort-algorithm. It gathers the
    exceptions which might occur in the sorting-threads in a single
    pre-allocated vector of exception_ptr's and moves this vector
    inside the exception which might be thrown later. If I would
    provide a copy-costructor or assignment-operator, this vector
    would be copied and an exception might get thrown. This might
    occur when you don't catch the exception by reference (I don't
    see any reason to catch exception-objects by value anyway). So
    there are good reasons to not to provide both.

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