Re: [boost] [function] function wrapping with no exceptionsafetyguarantee

Subject: Re: [boost] [function] function wrapping with no exceptionsafetyguarantee
From: Daniel Walker (daniel.j.walker_at_[hidden])
Date: 2010-10-25 16:27:13

On Fri, Oct 22, 2010 at 3:39 PM, Emil Dotchevski
<emil_at_[hidden]> wrote:
> On Fri, Oct 22, 2010 at 10:35 AM, Daniel Walker
> <daniel.j.walker_at_[hidden]> wrote:
>> Oops. Sorry, I spoke too soon. In fact, it IS currently possible for a
>> boost::function object to become empty due to a failed assignment. It
>> happens because the small object manager clones the target during a
>> call to swap(). If there is an exception during the allocation,
>> boost::function handles it, sets itself to empty and rethrows.
>
> Unless you can find specific documentation for this behavior (I
> couldn't), you can't assume that op= will leave the target empty upon
> failure.

True, but my point is that it is _possible_ for operator= to leave
boost::function empty. So if we change how the current implementation
of boost::function enters the empty state, we need to take account of
this case.

> AFAIK it provides only basic exception safety, meaning the
> state of the target is unspecified upon failure except that no memory
> will leak.

Changing boost::function's internal vtable from null to a static
"empty" vtable will not change the exception safety of any of its
member functions. However, it will increase the space overhead in the
data segment.

Daniel Walker