Logging only top-most ThreadContext stack item - log4net

Question

We're using Log4net's ThreadContext.Stacks and it is mostly working well. My problem comes if there have been multiple ThreadContext.Stacks["key"].Push(...).
With a simple ConversionPattern:
<param name="ConversionPattern value="... topProp=%properties{key} ..."/>
I see log entries like:
... topProp=first second third ...
I'd really like to see only the most recently pushed value rather than all the values. I had hoped I could put something like the following in my appender/layout/ConversionPattern:
<param name="ConversionPattern value="... topProp=%properties{key}{1} ..."/>
but that doesn't work. I can kludge it by assuming/requiring all values to be the same length (say 5) and doing:
<param name="ConversionPattern value="... topProp=%5.5properties{key} ..."/>
But that isn't real attractive. Any ideas?
Thanks!
[Edit to add very simple example]
using System;
using System.IO;
using log4net;
using log4net.Config;
namespace ThreadLocalExample {
class Program {
private const string PropJobId = "Example:JobId";
static void Main() {
XmlConfigurator.Configure(new FileInfo("log4net.cfg"));
var log = LogManager.GetLogger(typeof(Program));
ThreadContext.Stacks[PropJobId].Push("Old");
log.Debug("Enter using");
using (ThreadContext.Stacks[PropJobId].Push("New")) {
log.Debug("stuff");
}
log.Debug("Out of using");
log.Debug("done.");
Console.ReadKey();
}
}
}
With the log4net configuration:
<appender name="Console" type="log4net.Appender.ConsoleAppender">
<threshold value="ALL" />
<layout type="log4net.Layout.PatternLayout">
<param name="ConversionPattern" value="[jobId=%P{Example:JobId}]: %m%n" />
</layout>
</appender>
Produces:
[jobId=Old]: Enter using
[jobId=Old New]: stuff
[jobId=Old]: Out of using
[jobId=Old]: done.
But I'd like:
[jobId=Old]: Enter using
[jobId=New]: stuff
[jobId=Old]: Out of using
[jobId=Old]: done.

Answer 1

I had the same problem, and it was not only about 'bad formatting', because I used database appender (AdoNetAppender) which expects integers. So after joining all stacked values together the result is not an integer any more. Consider an appender like this:
<appender name="DbAppender" type="log4net.Appender.AdoNetAppender">
...
<commandText value="INSERT INTO Log ([Id]) VALUES (#Id)" />
<parameter>
<parameterName value="#Id" />
<dbType value="Int32" />
<layout type="log4net.Layout.PatternLayout" value="%P{someId}" />
</parameter>
This appender will not accept any log message, where 'someId' is stacked twice or more - no logs in database ...
So, to solve this problem I gave up with stacks and turned back to flat properties.
I've coded some short extension:
public static class Log4NetExt {
public static IDisposable ThreadContextPush(string key, object value) {
object oldVal = ThreadContext.Properties[key];
ThreadContext.Properties[key] = value;
var topMostCleaner = new DispCleaner();
topMostCleaner.EvDispose += () => {
// Pop = restore old value
ThreadContext.Properties[key] = oldVal;
};
return topMostCleaner;
}
private class DispCleaner : IDisposable {
public event Action EvDispose;
public void Dispose() {
if (EvDispose != null) EvDispose();
}
}
}
And now, instead of:
using (ThreadContext.Stacks[PropJobId].Push("New")) {
write:
using (Log4NetExt.ThreadContextPush(PropJobId, "New")) {
and it works ok ;)
(This short code does not follow all best practises of building disposable objects, deleting event handlers and all this stuff, but it is short and I think it is safe in this simple case).

Answer 2

I have Done it via Filip solution modified as
public static class Log4NetExt
{
public static IDisposable ThreadContextSet(string key, object value)
{
//object oldVal = ThreadContext.Properties[key];
ThreadContext.Properties[key] = value;
var topMostCleaner = new DispCleaner();
topMostCleaner.EvDispose += () => {
// Pop = restore old value
//ThreadContext.Properties[key] = oldVal;
ThreadContext.Properties[key] = null;
};
return topMostCleaner;
}
private class DispCleaner : IDisposable
{
public event Action EvDispose;
public void Dispose()
{
if (EvDispose != null)
{
EvDispose();
}
}
}
}
And used it like
using (Log4NetExt.ThreadContextSet("ContextId", "Feed"))
using (Log4NetExt.ThreadContextPush("ContextValue", objFeed.FeedId))
{
}