Re: [boost] Candidate logging library and static initialization/destruction

From: John Torjo (john.groups_at_[hidden])
Date: 2007-11-26 05:40:40

Hi Matthew,
> Hi,
>
> I have a question for the author of the logging library on the boost 
> review queue regarding static initialization and destruction.
>
>   
That would be me ;)
> I currently use the logging library that was rejected at the last 
> review, and I noticed some issues with it relating to handling 
> destruction in a static context. Specifically, I'd get occasional 
> segfaults if I declared an item in static scope that logged in its 
> destructor. Once the object was moved to within the main() function, the 
> issue went away. I'm not sure if it was the logging library, or our use 
> of it, but it was a bit of an issue since it made the use of logging 
> less transparent to clients of my library code.
>
>   
I have encountered this as well - in v1.
Right now, in v2 - at this time I'm not handling this. However, it's a 
must have to be in there (see todo.html - on the code in SVN).
So, within a week - this feature will be present.

> I can see from the documentation that you have given quite a bit of 
> thought to multithreading concerns. Have you also considered issues 
> around static initialization and destruction?
>
>   
Yes I have.
As a side-note - if you could trim down the example and send it to me, 
that would make it easier for me to test ;)

> In particular, a class that performs logging in its constructor and 
> destructor should still behave correctly when instantiated in a static 
> context. I think the problems I had with logging before related to the 
>   
Yes, that is true.
> The way I solved that in a (far more limited!) logging library for our 
> own use was the following:
>
> - Never destroy the logging data structures -- allow them to leak. No 
> risk of static ordering issues.
> - In the static initialization case, initialize the logging structures 
> on first access, and if not accessed during the static context, 
> guarantee that they are initialized before main() is called.
>
> To do that, I essentially borrowed the implementation of the boost pool 
> singleton, except that I removed the destruction:
>
> http://boost.org/libs/pool/doc/implementation/singleton.html
>
>   
Note: at this time, there are no problems at the logs' construction 
(related to segfaults or anything) - however, if you log from a 
constructor, nothing happens.
This needs to be fixed.
> Anyway, I would appreciate hearing your thoughts on this area as I'd 
> like to use version 2!
>
>   
So would I ;)

Best,
John

-- 
http://John.Torjo.com -- C++ expert
... call me only if you want things done right