Re: [boost] [thread] 1.41.0 regression

Subject: Re: [boost] [thread] 1.41.0 regression
From: Anthony Williams (anthony.ajw_at_[hidden])
Date: 2009-12-16 03:09:54

Dmitry Goncharov <dgoncharov_at_[hidden]> writes:

> The thread_data_base constructor is defined in a header file. Function
> make_external_thread_data() is defined in a .cpp file. This can lead
> to a situation when different libraries contain the definitions of
> these functions. The example below explains how this can happen and
> why this causes problems.

It always causes problems if your program has two incompatible
definitions of the same structure. It's a violation of the One
Definition Rule.

> There is a library (e.g. libuser.so) which uses the Boost.Thread
> library. Since the thread_data_base constructor is defined in a header
> file libuser.so can contain its definition.
> Again, the size of thread_data_base object, that the thread_data_base
> constructor from libuser.so expects, depends on if libuser.so was
> built with _GLIBCXX_DEBUG defined or not.
>
> An application cannot link agains both libboost_thread.so and
> libuser.so if these libraries were built with different _GLIBCXX_DEBUG
> definitions (or different alignment, etc).
> While loading the application the dynamic linker will use the
> definition of thread_data_base constructor either from libuser.so be
> or from libboost_thread.so. Whichever it finds first.
>
> Can both the thread_data_base constructor and
> make_external_thread_data() reside either in a .cpp file or in a
> header?

That won't make any difference. All the thread structures that are
defined in header files must have the same layout in the app as in the
thread library, otherwise you will either get linker errors or (worse)
runtime errors due to incorrect structure offsets.

The solution is to use the same compiler flags when you build your
application as when you build the boost thread library, to ensure that
the structures have the same layout.

Anthony
-- 
Author of C++ Concurrency in Action     http://www.stdthread.co.uk/book/
just::thread C++0x thread library             http://www.stdthread.co.uk
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