[LOG4NET-605] AdoNetAppenderIssue Multithreaded Application Freeze

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.0.8
• Component/s: Core
• Environment: Windows, MS SQL Server 2016
• Assignee: Unassigned
• Reporter: Sebastian Morgenbesser
• Created: 17/Jul/18 11:37
• Updated: 04/Apr/20 22:28

Description

I recently noticed a strange issue with log4net and the AdoNetAppender and it would be nice if anyone could comment on this.

Its quite an Edge Case I know but the implication is that the Application will freeze and no Exception is thrown which is kind of scary.

I have made a small example C# project to illustrate the issue which I can provide, but first I want to explain the issue.

The scenario is like this:

• Visual Studio C# Console Application. Log4net (latest version) embedded as dll, MS SQL Server 2016 (but I guess this doesn't matter), .NET Framework > 4.5
• The Application starts and the Logger is initialized (containing a AdoNetAppender pointing to an existing Database on MS SQL Server - localhost)
  • The code is something like this:
• After that happened, the Application is going to DROP the Database containing the Table that log4net will log to and recreates the database with all tables
  • This happens because every time the console starts the Log-Database should be empty  (I know there are other ways like truncate oder Drop Table but lets stay with me to understand the problem)
• So at this point the Database containing the Log Table has been recreated.
• Now the Application starts a number Threads (in my example 64, but I guess it works with less) and waits for them to finish
• In the Do() Method of the Thread, the thread simply tries to log an Error Message to the previously initialized logger
• The Result is that the Application freezes and will never return (0% CPU). Also no log messages arrive in the database.
• I am guessing there is some kind of deadlock situation inside log4net if multiple threads try to "initialize" the database connection to the recreated database again but in detail I have no idea what happens.
• No exception is thrown, the threads just never finish there Do() Method

 So if I skip the part where I Recreate the database (with DROP und CREATE Database), then it works.

Also if put a log statement after the recreation of the database but BEFORE the multithreaded part starts, it also works.