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  1. Log4net
  2. LOG4NET-605

AdoNetAppenderIssue Multithreaded Application Freeze



    • Type: Bug
    • Status: Open
    • Priority: Major
    • Resolution: Unresolved
    • Affects Version/s: 2.0.8
    • Fix Version/s: None
    • Component/s: Core
    • Labels:
    • Environment:
      Windows, MS SQL Server 2016


      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.


        1. log4etbugshowcase_visual_studio_project.zip
          418 kB
          Sebastian Morgenbesser



            • Assignee:
              sebi0707 Sebastian Morgenbesser
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