log4net.config

 <?xml version="1.0" encoding="UTF-8"?>
 <log4net>
   <root>
     <level value="all" />
     <appender-ref ref="LogFileAppenderByDate" />
   </root>
   <appender name="LogFileAppenderByDate" type="log4net.Appender.RollingFileAppender" >
     <param name="AppendToFile" value="true" />
     <!--最小锁定模型以允许多个进程可以写入同一个文件-->
     <param name="LockingModel" value="log4net.Appender.FileAppender+MinimalLock" />
     <param name="StaticLogFileName" value="true" />
     <param name="File" value="Log\\" />
     <param name="DatePattern" value="yyyyMM\\yyyy-MM-dd'.txt'" />
     <param name="StaticLogFileName" value="false" />
     <param name="RollingStyle" value="Composite" />
     <maxSizeRollBackups value="-1" />
     <maximumFileSize value="2MB" />
     <layout type="log4net.Layout.PatternLayout">
       <param name="ConversionPattern" value="%n-----%d-----%n%level%n%c%nline %L%n%m%n" />
     </layout>
   </appender>
 </log4net>

注意：<!--最小锁定模型以允许多个进程可以写入同一个文件-->

 <param name="LockingModel" value="log4net.Appender.FileAppender+MinimalLock" />

上面的配置经测试是错误的，提示被进程占用，应该是以下的配置：

 <?xml version="1.0" encoding="UTF-8"?>
 <log4net>
   <root>
     <level value="all" />
     <appender-ref ref="LogFileAppenderByDate" />
   </root>
   <appender name="LogFileAppenderByDate" type="log4net.Appender.RollingFileAppender" >
     <lockingModel type="log4net.Appender.FileAppender+MinimalLock" />
     <param name="AppendToFile" value="true" />
     <param name="StaticLogFileName" value="true" />
     <param name="File" value="Log\\" />
     <param name="DatePattern" value="yyyyMM\\yyyy-MM-dd'.txt'" />
     <param name="StaticLogFileName" value="false" />
     <param name="RollingStyle" value="Composite" />
     <maxSizeRollBackups value="-1" />
     <maximumFileSize value="2MB" />
     <layout type="log4net.Layout.PatternLayout">
       <param name="ConversionPattern" value="%n-----%d-----%n%level%n%c%nline %L%n%m%n" />
     </layout>
   </appender>
 </log4net>