[squid-dev] g++ 4.8.x and std::regex poblems

[Amos Jeffries]

On 30/11/2016 10:23 p.m., Christos Tsantilas wrote:
> On 29/11/2016 09:46 μμ, Amos Jeffries wrote:
>> I'm thinking it might be useful to add a how-to in the release notes for
>> v4+ to make the compiler update easier. Would you be able to write that
>> now that you have gone through the process?
> 
> I upgraded to newer OS, not just the compiler :-). It is something I
> would have to do in the next months so I decide to do it now.
> However major linux distributions still does not provide stable releases
> with gcc-5.x.
> 
>>
>> It is faster, but also has a different pattern syntax and API. So we
>> would need both a config directive to specify what syntax was in use and
>> a wrapper layer for portability.
>>
>> Which is exactly what std::regex provides . Though I have not gone so
>> far as to add the config directive for changing the used syntax. It
>> makes a lot more sense to go through the transition pain once instead of
>> twice (GNURegex -> PCRE -> std::regex).
> 
> My sense is that std::regex is not a wrapper layer. It is just a
> different implementation. Maybe it is the faster implementation, OK.

Whether its a wrapper or completely different implementation is up to
the library. At the very least it is a consistent API regardless of the
regex grammar being presented.

And the extra requirement of std::regex is that all 6 grammars be
presented one way or another, not limited to a subset of them the
library wants to implement.


> 
> We are using regex expressions in very few places and actually I believe
> that we should use RegexPattern class instead of direct calls to the
> external regex libraries. A such RegexPattern class can be small and can
> be adjusted to use many regex implementations.
> 

That is what the class was made for, yes.

> 
> I know that this is a new project, I am not saying that we should
> implement support for multiple regex libraries right now, but I believe
> that it is something we should have in our mind when we are planning squid.
> 

My point was that we dont have to. All we have to do is migrate to
std::regex usage and the underlying library is no longer our concern.

Once we are using std::regex we just add squid.conf flag(s) in relevant
places to set a users prefered grammar. The RegexPattern class sends
std::regex API a grammar flag depending on what the user configured.

The C++11 implementation guarantees availability of all the common
grammars as listed in the first table at
<http://www.cplusplus.com/reference/regex/regex_constants/#syntax_option_type>.
No worries about detecting libraries or what to link against for
multiple grammar support.


But them nice toys are stuck waiting for the CentOS 7 compiler to be
irrelevant. I hope we dont have to wait the next 14 years for its EOL date.

Amos