Re: [PATCH] Add configure flag for operator new (std::nothrow)

[Daniel Gutson <daniel.gutson@tallertechnologies.com>]

On Tue, Nov 10, 2015 at 10:10 AM, Jonathan Wakely <jwakely@redhat.com> wrote:
> On 06/11/15 09:59 +0000, Pedro Alves wrote:
>>
>> On 11/06/2015 01:56 AM, Jonathan Wakely wrote:
>>>
>>> On 5 November 2015 at 23:31, Daniel Gutson
>>
>>
>>>> The issue is, as I understand it, to do the actual work of operator
>>>> new, i.e. allocate memory. It should force
>>>> us to copy most of the code of the original code of operator new,
>>>> which may change on new versions of the
>>>> STL, forcing us to keep updated.
>>>
>>>
>>> It can just call malloc, and the replacement operator delete can call
>>> free.
>>>
>>> That is very unlikely to need to change (which is corroborated by the
>>> fact that the default definitions in libsupc++ change very rarely).
>>
>>
>> Or perhaps libsupc++ could provide the default operator new under
>> a __default_operator_new alias or some such, so that the user-defined
>> replacement can fallback to calling it.  Likewise for op delete.

that would allow us to overload operator new as something like this:

void* operator new  ( std::size_t count, const std::nothrow_t& tag)
noexcept(true)
{
    const auto old_handler = std::set_new_handler(nullptr);
    const auto ret = __default_operator_new(count, tag);
    std::set_new_handler(old_handler);
    return ret;
}

This is a non-iterating operator new.

This additional user defined operator new would be possible:

void* operator new  ( std::size_t count, const std::nothrow_t& tag)
noexcept(true)
{
    const auto old_handler = std::set_new_handler(nullptr);
    const auto ret = __default_operator_new(count, tag);
    std::set_new_handler(old_handler);

    if (ret == nullptr && old_handler != nullptr)
        old_handler();

    return ret;
}

So I like the idea.


>
>
> That could be useful, please file an enhancement request in bugzilla
> if you'd like that done.



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Daniel F. Gutson
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