When is Log4Net configured?

Question

Given that you have

[assembly: log4net.Config.XmlConfigurator(ConfigFile = "Log4Net.config", Watch = true)]

in your AssemblyInfo.cs file, when is Log4Net configured? Is it at the application start or when you use a logger for the first time?

Answer 1

The config file is used when you cause a call to the LoggerManager class. This is usually caused by calling LogManager.GetLogger.

See http://logging.apache.org/log4net/release/sdk/log4net.Config.XmlConfiguratorAttribute.html for more details; specifically the note:

Log4net will only look for assembly level configuration attributes once. When using the log4net assembly level attributes to control the configuration of log4net you must ensure that the first call to any of the LoggerManager methods is made from the assembly with the configuration attributes.

Answer 2

A quote from the Apache log4net site:

Therefore if you use configuration attributes you must invoke log4net to allow it to read the attributes. A simple call to LogManager.GetLogger will cause the attributes on the calling assembly to be read and processed. Therefore it is imperative to make a logging call as early as possible during the application start-up, and certainly before any external assemblies have been loaded and invoked. http://logging.apache.org/log4net/release/manual/configuration.html

Here is a good article on how to make sure the configuration is set up and run properly: http://www.fooji.net/blog/post/2010/04/27/logging-log4net-e28093-part-iii.aspx

Basically, you need to either make a logging call (which configures log4net if it isn't already configured) or utilize the DOMConfigurator to manually configure log4net.