log4cpp-devel

[Log4cpp-devel] How does one "destroy" a category?

[<log...@li...>]

Hi all,

A silly question, I'm looking to use log4cpp for a data collection
system I'm working on.

To help in post mortem analysis it's often useful to separate out log
messages by some common key to be able to piece out what happened.  The
system starts multiple transaction state machines each identified by a
unique ID, creating them at runtime.  They are one-shot, so once
complete, the objects are freed.

It appears it would make sense for each transaction state machine to
have its own log category, as the log messages can then be grepped for
and it ensures *every* log message from that log instance will have the
ID prepended.

It seems I can create as many category objects as I like, but what isn't
clear is what happens to the category objects when they're no longer
needed: I don't see any way to close them off or destroy them.  (I could
call delete(&category); but I'm not sure where else the pointer may be
used.)

Is there a way to remove categories once they're no longer in use?
Regards,
-- 
     _ ___             Stuart Longland - Systems Engineer
\  /|_) |                           T: +61 7 3535 9619
 \/ | \ |     38b Douglas Street    F: +61 7 3535 9699
   SYSTEMS    Milton QLD 4064       http://www.vrt.com.au

Re: [Log4cpp-devel] How does one "destroy" a category?

[<log...@li...>]

On 3/15/15, 7:25 PM, "log...@li..." <log...@li...> wrote:

>It appears it would make sense for each transaction state machine to
>have its own log category, as the log messages can then be grepped for
>and it ensures *every* log message from that log instance will have the
>ID prepended.

I think you want to use a diagnostic context, not a category. Just push and pop the ID with the NDC routines.

(And you can't really destroy a category, so that's why it's a bad choice to use that.)

-- Scott

Re: [Log4cpp-devel] How does one "destroy" a category?

[<log...@li...>]

Hello Stuart,

The categories in current design are seen as purposed for kind of static
matters, those which do not actively come into the processing and leave it.
There is static helper method to make their creation convenient and
controlled. However, there is no destroy method since the pointer given out
might still be kept somewhere else, out of log4cpp internals.
If you'd like to have an unique id coming along with your log messages, you
could take advantage of the NDC feature. It is exactly purposed for
attaching kind of context to the log messages. It can be turned on and off
from properties file without rebuilding, but note that is linked with a
thread, and not with the particular category.
If your processing is not thread-based, won't it be easier to log the id
just as a part of the message itself?

Alexander.
 On Mar 16, 2015 3:26 AM, <log...@li...> wrote:

> Hi all,
>
> A silly question, I'm looking to use log4cpp for a data collection
> system I'm working on.
>
> To help in post mortem analysis it's often useful to separate out log
> messages by some common key to be able to piece out what happened.  The
> system starts multiple transaction state machines each identified by a
> unique ID, creating them at runtime.  They are one-shot, so once
> complete, the objects are freed.
>
> It appears it would make sense for each transaction state machine to
> have its own log category, as the log messages can then be grepped for
> and it ensures *every* log message from that log instance will have the
> ID prepended.
>
> It seems I can create as many category objects as I like, but what isn't
> clear is what happens to the category objects when they're no longer
> needed: I don't see any way to close them off or destroy them.  (I could
> call delete(&category); but I'm not sure where else the pointer may be
> used.)
>
> Is there a way to remove categories once they're no longer in use?
> Regards,
> --
>      _ ___             Stuart Longland - Systems Engineer
> \  /|_) |                           T: +61 7 3535 9619
>  \/ | \ |     38b Douglas Street    F: +61 7 3535 9699
>    SYSTEMS    Milton QLD 4064       http://www.vrt.com.au
>
>
> ------------------------------------------------------------------------------
> Dive into the World of Parallel Programming The Go Parallel Website,
> sponsored
> by Intel and developed in partnership with Slashdot Media, is your hub for
> all
> things parallel software development, from weekly thought leadership blogs
> to
> news, videos, case studies, tutorials and more. Take a look and join the
> conversation now. http://goparallel.sourceforge.net/
> _______________________________________________
> Log4cpp-devel mailing list
> Log...@li...
> https://lists.sourceforge.net/lists/listinfo/log4cpp-devel
>

Re: [Log4cpp-devel] How does one "destroy" a category?

[<log...@li...>]

Hi Scott and Alexander,
On 16/03/15 09:39, log...@li... wrote:
> On 3/15/15, 7:25 PM, "log...@li..." <log...@li...> wrote:
> 
>> It appears it would make sense for each transaction state machine to
>> have its own log category, as the log messages can then be grepped for
>> and it ensures *every* log message from that log instance will have the
>> ID prepended.
> 
> I think you want to use a diagnostic context, not a category. Just push and pop the ID with the NDC routines.
> 
> (And you can't really destroy a category, so that's why it's a bad choice to use that.)

On 16/03/15 15:57, log...@li... wrote:
> The categories in current design are seen as purposed for kind of static
> matters, those which do not actively come into the processing and leave
> it. There is static helper method to make their creation convenient and
> controlled. However, there is no destroy method since the pointer given
> out might still be kept somewhere else, out of log4cpp internals.
> If you'd like to have an unique id coming along with your log messages,
> you could take advantage of the NDC feature. It is exactly purposed for
> attaching kind of context to the log messages. It can be turned on and
> off from properties file without rebuilding, but note that is linked
> with a thread, and not with the particular category.
> If your processing is not thread-based, won't it be easier to log the id
> just as a part of the message itself?

I'm doing some further research into this, NDC sounds closer to what I'm
after, however one things that concerns me is that it appears I need to
manually push my context onto it each time I enter a context rather than
just writing to an object that does this for me.

Basically what I'm after, is an object that I can hold either by
reference or pointer, that when I write to it, it applies the necessary
tagging to identify that line in the log and know where it came from.

Categories aren't ideal, but it does achieve this in a structured
manner.  I don't have to remember to tell it that I'm in a transaction
state machine context (which may be in a separate thread) or have to
remember to remove it at the end.

I'll do some more digging and see what I can uncover, but this looks
like it gets at least part-way there.
-- 
     _ ___             Stuart Longland - Systems Engineer
\  /|_) |                           T: +61 7 3535 9619
 \/ | \ |     38b Douglas Street    F: +61 7 3535 9699
   SYSTEMS    Milton QLD 4064       http://www.vrt.com.au

Re: [Log4cpp-devel] How does one "destroy" a category?

[<log...@li...>]

On 3/16/15, 11:33 PM, "log...@li..." 
<log...@li...> wrote:


>
>I'm doing some further research into this, NDC sounds closer to what I'm
>after, however one things that concerns me is that it appears I need to
>manually push my context onto it each time I enter a context rather than
>just writing to an object that does this for me.

Yes, but you can wrap all that into your classes via c'tors and d'tors so 
that it's automatic if you design things right.

>Basically what I'm after, is an object that I can hold either by
>reference or pointer, that when I write to it, it applies the necessary
>tagging to identify that line in the log and know where it came from.

You could also wrap the Category interface so that when you call methods 
on it, it pushes/pops the NDC for you before calling the category methods.

-- Scott

Re: [Log4cpp-devel] How does one "destroy" a category?

[<log...@li...>]

On 17/03/15 09:35, log...@li... wrote:
> On 3/16/15, 11:33 PM, "log...@li..." 
> <log...@li...> wrote:
> 
> 
>>
>> I'm doing some further research into this, NDC sounds closer to what I'm
>> after, however one things that concerns me is that it appears I need to
>> manually push my context onto it each time I enter a context rather than
>> just writing to an object that does this for me.
> 
> Yes, but you can wrap all that into your classes via c'tors and d'tors so 
> that it's automatic if you design things right.
> 
>> Basically what I'm after, is an object that I can hold either by
>> reference or pointer, that when I write to it, it applies the necessary
>> tagging to identify that line in the log and know where it came from.
> 
> You could also wrap the Category interface so that when you call methods 
> on it, it pushes/pops the NDC for you before calling the category methods.

Indeed, for now I'll see how the following goes.

	class LogContext {
		public:
			LogContext(log4cpp::Category& log,
					const std::string& context)
			: log(log)
			{
				log4cpp::NDC::push(context);
			}

			~LogContext()
			{
				log4cpp::NDC::pop();
			}

			log4cpp::Category&	log;
	};

The idea being it gets allocated on the stack, and will be popped off
when the function exits.  This might do the trick.
-- 
     _ ___             Stuart Longland - Systems Engineer
\  /|_) |                           T: +61 7 3535 9619
 \/ | \ |     38b Douglas Street    F: +61 7 3535 9699
   SYSTEMS    Milton QLD 4064       http://www.vrt.com.au