Hi James,
From tests that I have carried out we can easily get a couple of orders of magnitude perf improvements by not formatting our strings at runtime, but leaving it to a post processor. This makes the difference between logging being feasible or not in high
The boost logging library does not seem to support late formatting of strings. performance sections of code.
There are different ways to achieve this. One of them, using boost::logging, is to make a logger: - uses tags - that logs on a dedicated thread. Thus, when you log a message, internally, the message is gathered, tags are gathered as well, and placed into a queue. Then, only on the dedicated thread, the other thread formatting occurs and then the message is written to the destination(s). Example of writing on a dedicated thread: http://torjo.com/log2/doc/html/ded__loger__one__filter_8cpp-example.html
Clearly late formatting is difficult because it requires the collation of manifest data of some kind for every log message. My implementation simply logs the boost::format string the first time the log message occurs - but that does mean that it's very awkward to turn logging on and off at run time.
Why is it awkward? As a side-note : there are many ways to reduce the logging time. One of them is to, when logging, to internally use an optimized string: http://torjo.com/log2/doc/html/namespaceboost_1_1logging_1_1optimize.html Side note 2: to profile the logging time is really easy: http://torjo.com/log2/doc/html/namespaceboost_1_1logging_1_1profile.html
An alternative implementation is the Windows WPP library, which runs a preprocessor and puts the results into the symbols files (much more difficult to make cross platform).
Have I missed a way to use late formatting with boost::logging? Are there any intentions to introduce late formatting to boost::logging?
Note: the boost::logging is extremely flexible. For instance, you can create your own gather_msg class, which uses as many late formatting techniques as you wish. http://torjo.com/log2/doc/html/workflow.html#workflow_2a So for instance you can easily use gather using boost::format, and do the formatting / write to destinations on a dedicated thread. Best, John -- http://John.Torjo.com -- C++ expert http://blog.torjo.com ... call me only if you want things done right