Tom Lane wrote:
> Craig Ringer <craig@xxxxxxxxxxxxxxxxxxxxx> writes:
> > On 01/06/10 11:05, Tom Lane wrote:
> >> I'd be interested to see a section like this written by someone who'd
> >> actually done a nontrivial C++ extension and lived to tell the tale.
>
> > I can't speak up there - my own C++/Pg backend stuff has been fairly
> > trivial, and has been where I can maintain a fairly clean separation of
> > the C++-exposed and the Pg-backend-exposed parts. I was able to keep
> > things separate enough that my C++ compilation units didn't include the
> > Pg backend headers; they just exposed a pure C public interface. The Pg
> > backend-using compilation units were written in C, and talked to the C++
> > part over its exposed pure C interfaces.
>
> Yeah, if you can design your code so that C++ never has to call back
> into the core backend, that eliminates a large chunk of the pain.
> Should we be documenting design ideas like this one?
I have incorporated the new ideas into the C++ documentation section,
and removed the comment block in the attached patch.
--
Bruce Momjian <bruce@xxxxxxxxxx> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ None of us is going to be here forever. +
Index: doc/src/sgml/extend.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/extend.sgml,v
retrieving revision 1.42
diff -c -c -r1.42 extend.sgml
*** doc/src/sgml/extend.sgml 1 Jun 2010 03:19:36 -0000 1.42
--- doc/src/sgml/extend.sgml 2 Jun 2010 01:20:23 -0000
***************
*** 273,280 ****
&xoper;
&xindex;
- <!-- Use this someday when C++ is easier to use. bjm 2010-05-31
-
<sect1 id="extend-Cpp">
<title>Using C++ for Extensibility</title>
--- 273,278 ----
***************
*** 284,313 ****
<para>
It is possible to use a compiler in C++ mode to build
! <productname>PostgreSQL</productname> extensions; you must simply
! follow the standard methods for dynamically linking to C executables:
<itemizedlist>
<listitem>
<para>
! Use <literal>extern C</> linkage for all functions that must
! be accessible by <function>dlopen()</>. This is also necessary
! for any functions that might be passed as pointers between
! the backend and C++ code.
! </para>
! </listitem>
! <listitem>
! <para>
! Use <function>palloc()</> to allocate any memory that might be
! freed by the backend C code (don't pass <function>new()</>-allocated
! memory).
</para>
</listitem>
<listitem>
<para>
! Use <function>pfree()</> to free memory allocated by the backend
! C code (do not use <function>delete()</> for such cases).
! </para>
</listitem>
<listitem>
<para>
--- 282,307 ----
<para>
It is possible to use a compiler in C++ mode to build
! <productname>PostgreSQL</productname> extensions by following these
! guidelines:
<itemizedlist>
<listitem>
<para>
! All functions accessed by the backend must present a C interface
! to the backend; these C functions can then call C++ functions.
! For example, <literal>extern C</> linkage is required for
! backend-accessed functions. This is also necessary for any
! functions that are passed as pointers between the backend and
! C++ code.
</para>
</listitem>
<listitem>
<para>
! Free memory using the appropriate deallocation method. For example,
! most backend memory is allocated using <function>palloc()</>, so use
! <function>pfree()</> to free it, i.e. using C++
! <function>delete()</> in such cases will fail.
</listitem>
<listitem>
<para>
***************
*** 320,325 ****
</para>
</sect1>
- -->
</chapter>
--- 314,318 ----
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