Memory leaks with large multi-threaded application.

Hi folks,

I’m pretty sure I’ve found a large memory leak when running multi-threaded applications and using log4net tracing. I’ve isolated it down to log4net by commenting out the <log4net> node out of the configuration file.

We’ve coded log4net (the latest beta version 1.2.0-beta8) into our application. With log4net enabled we see our virtual memory increasing and never decreasing, over a period of time and particularly with stress testing the server runs out of memory and everything grinds to a halt.

I’m afraid I don’t have time to try and reproduce the problem in a sample project for you as I now need to look at switching back to release 1.0 of log4net to see if that will sort out the problem.

What I can point out to you is the following; I hope it helps in diagnosing the issue also I’ll include the configuration I’m using at the end of the mail.

1.      It happens with both FileAppenders and OutputDebugStringAppenders, I have not tried it with any others.
2.      When analyzing the memory usage using a memory profiler, the managed heap memory was fine all the memory seemed to be allocated to Win32.

3.      The number of handles used never decreases and gets very large, when running 50 simulatenous threads which have logging contained in their execution paths then number of handles in the application rose to several thousand quite quickly.

4.      It happens in both debug and release builds of our application.
5.      I’m only using the release build of log4net for .NET version 1.1.
6.      The platform is WindowsXP Profession (for developers) and W2K Server deployment.
7.      Most annoyingly, it does not happen all the time. For example I noticed the memory issue a while ago and tried to trace it down. I did not pin it down and then it stopped happening. We deployed the software to a test server (W2K) and it leaked like a sieve as soon as it started running there. I spent 2 days tracking down the problem and then the W2K machine stopped leaking memory without any changes been applied. The W2K machine had been rebooted several times over the course of those 2 days.

8.      Once it does start leaking memory, it keeps leaking memory after every run. Commenting out the log4net node in the config file, stops the memory leak and commenting it back in again starts the memory leak.

9.      You have to comment out the log4net node for it to stop, setting the reporting level to ERROR or FATAL when nothing should normally be logged still reproduces the leak.

I’m not joking about this bug or trying to lead you up the garden path. Please feel free to contact me about any questions you have, my business email address and contact details are below. Like I said, I’d love to get a small sample project together to reproduce this issue but we are under severe time constrains on the project delivery (isn’t everyone).

Here’s the configuration node I am using.

        <log4net>

                <appender name="FileAppender" type="log4net.Appender.FileAppender">

                        <param name="File" value="log-file.txt" />

                        <param name="AppendToFile" value="true" />

                        <layout type="log4net.Layout.PatternLayout">

                                <param name="ConversionPattern" value="%d [%t] %-5p %c [%x] %M - %m%n" />

                        </layout>

                </appender>

                <appender name="OutputDebugStringAppender" type="log4net.Appender.OutputDebugStringAppender" >

                        <layout type="log4net.Layout.PatternLayout">

                                <param name="ConversionPattern" value="%d\t[%t]\t%-5p\t%c\t[%x]\t%m%n" />

                        </layout>

                </appender>

                <root>

                        <level value="Error" />

        <!--            <appender-ref ref="OutputDebugStringAppender" /> -->

                        <appender-ref ref="FileAppender" />

                </root>

        </log4net>

Here’s a sample of how we are using it in code.

        Initialized by the following code..

        log4net.Config.DOMConfigurator.Configure()

        _Log.Info("Initialised Logging")

        Utilized in a class by the following

    Private Shared _Log As log4net.ILog = log4net.LogManager.GetLogger(GetType(PoolManager))

        Here’s a sample method of a class method with logging contained.

    Public Shared Sub [Stop]()

        _Log.Info("Push")

        Try

            SyncLock _LockContext

                '----------------------------------------------------------------------------------------------------

                ' Stop the service but only if it was started, again we want to proivide synchronous access to this

                ' request so we put a SyncLock (Monitor object) around the block.

                '----------------------------------------------------------------------------------------------------

                If _State = StateEnum.Starting OrElse _State = StateEnum.Started Then

                    _State = StateEnum.Stopped

                    ConnectionMonitor.StopMonitoring()

                    Call LogoutPoolUsers()

                    _State = StateEnum.Stopped

                Else

                    _Log.Warn("Attempting to stop the pool manager when it was not started.....")

                End If

            End SyncLock

        Catch ex As Exception

            _Log.Error(ex)

            Throw

        End Try

        _Log.Info("Pop")

    End Sub

Noel Lysaght
Zarion Ltd.
3 Westland Square, Pearse St.
Dublin 2, Ireland.

Simplifying, Automating and Integrating Business Processes
Voice: +353-(0)1-240-5200               UK: +44-(0)20-7495-7511
Direct: +353-(0)1-240-5210
Fax:    +353-(0)1-670-7868              UK: +44-(0)20-7153-4401
Web:   <www.zarion.com>
Email:  nlysaght@xxxxxxxxxx <mailto:nlysaght@xxxxxxxxxx>

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