Re: [boost] Re: Logging Library -- Formal Review Request

From: Mark Blewett (boost_at_[hidden])
Date: 2005-04-30 17:11:54

At 19:03 29/04/2005, you wrote:
>John Torjo wrote:
>>I've just updated the Boost Log Library:
>>http://torjo.com/code/logging-v132.zip
>
>It's good to see progress on logging and what I've seen so far looks 
>promising. However...
>
>>BOOST_LOG(app) << "testing " << i << '-' << j << '-' << k  << std::endl;
>>BOOST_LOG(dbg) << "this is a debug message, i=" << i << std::endl;
>>BOOST_LOG(info) << "I just wanted to tell you something....";
>
>...while I like the feeling of the stream approach from a user's perspective,

I agree.

>there is one (IMHO important) feature that can not be implemented with it: 
>Exception guards.
>
>To illustrate my point, consider a "pure MACRO approach" like this:
>
>std::string f()
>{
>    throw 42;
>}
>
>BOOST_LOG( app, "Huhu!" + f() );
>
>where BOOST_LOG is:
>
>#define BOOST_LOG( logger, message ) \
>do { if( logger.is_enabled() ) { \
>  try { logger.print( message ); } \
>  catch( const std::exception& e ) { \
>   logger.print( "Can't log \"" #message "\", e.what(): \"" + \
>                 std::string( e.what() ) + "\"" ); \
>  } \
>  catch( ... ) { \
>   logger.print( "Can't log \"" #message "\", unknown exception" ); \
>  } \
>} } while( false )

What happens if logger.print() throws (say because there isn't enough disk 
space to write a log to)?

I've always taken the other view (being a developer for server applications 
that have to run 24/7) that if you can't write to the log, you don't 
jeopardise the application.

>This feature helped us several times in the company when a log-message, 
>calling some complicated functions, failed in a production system. As long 
>as the above technique is applied, the log-file contains a good hint for 
>us what's wrong and the product is still running without the customer noticing.
>
>Regards, Daniel

Regards
Mark