Kea  2.3.5-git
asio_wrapper.h File Reference
#include <utility>
#include <boost/asio.hpp>
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Macros

#define GNU_CC_VERSION
 !!! IMPORTANT THIS IS A HACK FOR BOOST HEADERS ONLY BUILDING !!!! More...
 

Macro Definition Documentation

◆ GNU_CC_VERSION

#define GNU_CC_VERSION
Value:
(__GNUC__ * 10000 \
+ __GNUC_MINOR__ * 100 \
+ __GNUC_PATCHLEVEL__)

!!! IMPORTANT THIS IS A HACK FOR BOOST HEADERS ONLY BUILDING !!!!

As of #5215 (Kea 1.3) The default build configuration is to link with Boost's system library (boost_system) rather than build with Boost's headers only. Linking with the boost_system eliminates the issue as detailed below. This file exists solely for the purpose of allowing people to attempt to build headers only. ISC DOES NOT RECOMMEND building Kea with Boost headers only.

This file must be included anywhere one would normally have included boost/asio.hpp. Until the issue described below is resolved in some other fashion, (or we abandon support for headers only building) asio.hpp MUST NOT be included other than through this file.

The optimizer as of gcc 5.2.0, may not reliably ensure a single value returned by boost::system::system_category() within a translation unit when building the header only version of the boost error handling. See Trac #4243 for more details. For now we turn off optimization for header only builds the under the suspect GCC versions.

The issue arises from in-lining the above function, which returns a reference to a local static variable, system_category_const. This leads to situations where a construct such as the following:

{{{ if (ec == boost::asio::error::would_block || ec == boost::asio::error::try_again) return false; }}}

which involve implicit conversion of enumerates to error_code instances to not evaluate correctly. During the implicit conversion the error_code instances may be assigned differing values error_code:m_cat. This causes two instances of error_code which should have been equal to to not be equal.

The problem disappears if either error handling code is not built header only as this results in a single definition of system_category() supplied by libboost_system; or the error handling code is not optimized.

We're doing the test here, rather than in configure to guard against the user supplying the header only flag via environment variables.

We opened bugs with GNU and BOOST:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69789 https://svn.boost.org/trac/boost/ticket/11989

Todo:
Version 6.0 will need to be tested.

As of 2016-08-19, the version 5.4.0 from Ubuntu 16.04 is affected. Updated the check to cover everything that is not 6.0, hoping that 6.0 solves the problem.

Definition at line 67 of file asio_wrapper.h.