Re: Integrating C++ singletons into postgresql extensions???

Hello,

2014-10-18 3:59 GMT+04:00 Stephen Woodbridge <woodbri(at)swoodbridge(dot)com>:

> Hi,
>
> I've been writing C++ code that needs to get wrapped into a postgresql
> extension and it has a few singleton classes like:
>
> 1. Config object that holds some general configuration information.
> 2. Stats object for global stats collection.
> 3. Logger object for enabling/disabling debug logging to a file.
> 4. curlpp class for making outbound calls to an OSRM web service from the
> c++ code
>
> I can probably do without 1-3 if I had to when the code is integrated, but
> they are handy to keep around in the code for when we are developing and
> working outside the postgresql database. I could #ifdef then all, but I
> would like to avoid cluttering the code with tons of #ifdef.
>
> Item 4 is a little more problematic and needs to be kept around or
> something else implemented to take its place. I have looked at the curl
> extension and actual built another module in C that uses those ideas., but
> the curlpp is a nice OO class that encapsules and hides all the curl stuff
> from the C++ code.
>
> So my question(s) are:
>
> 1. Any insights into singletons working/not working within the postgresql
> server extensions? My understanding is that these are implemented as global
> static classes with a lifetime of the process and they have no destructor,
> so I'm a little worried about memory leaks or multiple queries sharing the
> singleton.
>
> 2. Is there another way implement the equivalent of a singleton for C++
> code that has a lifetime of the query in the server?
>
> 3. What do for logging classes when integrating C++ code into postgresql?
>
> Any help or ideas would be appreciated.
>
I would have written extension in pure C. And I would get rid of
singletones. (Singletone - artificial constraints that the programmer
creates for himself. Btw, C++ - too :-) )
I would use Extension Configuration Tables to store the
configuration
http://www.postgresql.org/docs/9.4/static/extend-extensions.html#AEN57238

--
// Dmitriy.