[squid-dev] FYI: the C++11 roadmap

[Amos Jeffries]

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On 6/11/2014 6:24 a.m., Marcus Kool wrote:
> On 6/11/2014 1:27 a.m., Marcus Kool wrote:
>> 
>> 
>> On 11/05/2014 02:01 AM, Amos Jeffries wrote: On 6/05/2014 2:21 
>> a.m., Amos Jeffries wrote:
>>>>> I have just announced the change in 3.4.5 regarding C++11 
>>>>> support and accompanied it with a notice that GCC verion
>>>>> 4.8 is likely to become the minimum version later this
>>>>> calendar year.
>>>>> 
>>>>> As it stands (discussed earlier):
>>>>> 
>>>>> * Squid-3.4 needs to build with any GCC 4.0+ version with 
>>>>> C++03.
>>>>> 
>>>>> * Squid-3.6 will need to build with C++11.
>>>>> 
>>>>> * The Squid-3.5 situation is still in limbo and will
>>>>> depend on how long we go before it branches.
>> 
>> Squid-3.5 retains GCC 4.0+ support shared with older versions.
>> 
>>>>> 
>>>>> We have a growing list of items needing C++11 features for 
>>>>> simpler implementation. At this point I am going to throw
>>>>> a peg out and say Sept or Oct for starting to use C++11 
>>>>> specific code features.
> 
>>> This "peg" has now moved to Nov. The code cleanup and
>>> polishing patches now going into trunk work fine with C++11
>>> builds but possibly not with compilers older than Clang 3.3 or
>>> GCC 4.8.
> 
> Are you referring here to building squid 3.5 or 3.6 ? Do you think
> that changing to C++11 is ok for both versions?


trunk == 3.6 and later now. 3.5 is feature-frozen for stable cycle.


> 
>>>> It is understandable that developers want to move forward. 
>>>> Almost everybody does. But system administrators tend to do
>>>> the opposite: they stay on a stable platform for as long as
>>>> possible while they wait for a new platform to mature. Lets
>>>> look at the most popular Linux server platform: Redhat 6 /
>>>> CentOS 6. Redhat 6 has gcc 4.4 while the successor Redhat 7
>>>> has gcc 4.8. This means that when Squid gets a new
>>>> requirement with gcc 4.8 the new versions will not run on
>>>> Redhat 6.
>>> 
>>>> Because Redhat 6 is the most popular and stable server
>>>> platform and Redhat 7 is not mature and does not meet my
>>>> expectations of a stable platform (especially systemd is
>>>> still a big troublemaker), this implies that choosing for
>>>> C++11 effectively means that new releases of Squid will not
>>>> be installed any longer on the most popular Linux server
>>>> platform.
>>> 
>>>> So I think my opinion from the point of view of a system 
>>>> administrator is clearly "choose for installability, choose 
>>>> C++03".
>> 
>> "If an admin is so dearly wanting aged-stability. What are they
>> doing building the latest Squid release in its youth?"
> 
> Admins do not want "the latest", they want "the latest proven". For
> me that is 3.4.9 and when 3.5.5 comes out, it is time to evaluate 
> upgrading.  Depends also on the number and nature of complaints on
> the mailing list.
> 
>> Seriously though, these are my reasons for the timing:
>> 
>> * Both clang 3.3 and gcc 4.8 were released in early 2013. By the
>> time these Squid-3.6 builds get near a beta release these
>> compiler versions will already be nearing their 3rd birthdays.
> 
> The man page of gcc 4.8 explains the -std=c11 like this: ISO C11,
> the 2011 revision of the ISO C standard.  Support is incomplete and
> experimental.

Sorry, rounding. The exact version may turn out to be 4.8.1 if we make
use of inheriting constructors.

> 
> The man page of gcc 4.9.1 has a new text: ISO C11, the 2011
> revision of the ISO C standard.  This standard is substantially
> completely supported, modulo bugs, extended identifiers (supported
> except for corner cases when -fextended-identifiers is used),
> floating-point issues (mainly but not entirely relating to optional
> C11 features from Annexes F and G) and the optional Annexes K
> (Bounds-checking interfaces) and L (Analyzability).
> 
> Not sure if we can rely on man pages; it seems that gcc 4.9 is a
> safer 'minimal requirement'.

I'm reading the C++ section of:
https://gcc.gnu.org/gcc-4.7/changes.html
https://gcc.gnu.org/gcc-4.8/changes.html
https://gcc.gnu.org/gcc-4.9/changes.html

The announcement text is in 4.9, but that series only includes C++1y
changes. The C++11 support is already finished in the earlier 4.8 series.

> 
>> * Most of C++11'isms expected to be useful are the early "C++0x" 
>> features (atomics, auto etc.) which are supported by GCC 4.4
>> from RHEL6 anyway. RHEL6 people just need to explicitly pass one
>> of the special C++0x flags when building. The reason for naming
>> those specific compilers is that they are the first to offer
>> *full* C++11 support. ** if someone wants to work on
>> auto-detecting RHEL6 / CentOS6.5 and auto-enabling that option,
>> great.
>> 
>> * It is growing more and more difficult to prevent useful
>> C++isms showing up. 
>> http://www.squid-cache.org/Versions/v3/3.5/changesets/squid-3-13627.patch
>>
>> 
took several days with clean rebuilds to even find out what the
>> problem was. Some like auto have now been around in the
>> literature and example code for 5+ years.
>> 
>> ...regarding RHEL and CentOS specifically...
>> 
>> * RHEL/CentOS are the only OS family which has this problem. The 
>> others are all on shorter or simply earlier cycles of turnover
>> and will be providing the compilers in their mainstream OS
>> versions by about the same time Squid-3.6 goes beta, if not
>> already now.
> 
> Suse 11 SP3 does not have gcc 4.8 either (only 4.7) Suse 12 is also
> not mature, so it has the same problem as Redhat 7.
> 
>> * If RHEL7 matches the same cycle as 6 and 5 before it did then
>> we can expect a RHEL7.1 in a couple of months when todays trunk
>> starts to get early adopters, and a RHEL7.2 around the end of
>> next year when todays trunk becomes Squid-3.6 beta. 7.4-ish being
>> the popular one approx. 1 year behind Squid-3.6 going stable.
>> Squid appears to have about a year lag in popularity anyway,
>> though Eliezers' packages are helping things change a bit there.
> 
> Most likely the systems with Redhat 6 stay on Redhat 6 for 18+
> months before upgrading to Redhat 7.

Understood, not being a RHEL user myself I am going by the visible
popularity. Which IME seems to grow about their .3/.4 release. That
seems to fit about 18months from a .1/.2 working version.
 I'm expecting ~24months advance with approx. 12month gap to bridge.

> So until they upgrade, they have gcc 4.4. Although I have no
> numbers on installed packages, it is very likely that Eliezers'
> packages indeed help.  I bet that if the packages would be 
> downloadable from squid-cache.org their popularity will increase.
> 
>> So now seems about right to introduce C++11.
> 
> I understand.
> 
> Marcus
> 

Amos

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