Re: [PATCH 3/4] libstdc++: avoid character accumulation in istreambuf_iterator

[Petr Ovtchenkov <ptr@void-ptr.info>]

On Thu, 16 Nov 2017 10:39:02 +0100
Paolo Carlini <paolo.carlini@oracle.com> wrote:

> Hi,
> 
> On 16/11/2017 06:31, Petr Ovtchenkov wrote:
> > Is we really worry about frozen sizeof of instantiated template? 
> Yes we do. See https://gcc.gnu.org/onlinedocs/libstdc++/manual/abi.html 
> under "Prohibited Changes", point 8.
> 
> Of course removing the buffering has performance implications too - 
> that's why it's there in the first place!

"buffering" here is a secondary buffering (after streambuf).
No relation to performance, but place for incoherence with
state of attached streambuf.

Of cause, I can spend time to measure the difference.

The main point of this patch series is avoidance of lost link between
streambuf and istream_iterator when istream_iterator see eof.
Implementations that forget about attached streambuf after
istream_iterator see eof (or lost synchronization with attached
streambuf) violate principles of C++ objects life cycle.
From practical point of view, such implementation block usage of
istream_iterator for sockets, ttys, etc. --- only non-modified
files remains in scope of application.


> - which I remember we 
> investigated a bit again in the past when somebody reported that a few 
> implementations had it other did not. But I can't say to have followed 
> all the (recently uncovered) conformance implications, it could well be 
> that we cannot be 100% conforming to the letter of the current standard 
> while taking advantage of a buffering mechanism. Jonathan will provide 
> feedback.
> 
> Paolo.

--

  - ptr