log4net
appender の設定に以下を追加 <lockingModel type="log4net.Appender.FileAppender+MinimalLock" /></lockingmodel>
<root> <level value="ALL" /> <appender-ref ref="EventLogAppender"/> </root> <appender name="EventLogAppender" type="log4net.Appender.EventLogAppender"> <filter type="log4net.Filter.LevelRangeFilter"> <levelMin value="ERROR" /> <levelMax value="FATAL" /> </filter> </appender>