File lock error when using FileAppender with XmlConfigurator.ConfigureAndWatch (v3.3.1)

When using the XmlConfigurator's file-watching, like this:

var logRepository = LogManager.GetRepository(typeof(Program).Assembly);
XmlConfigurator.ConfigureAndWatch(logRepository, new FileInfo("log.config"));

with a simple FileAppender config, like this:

<log4net>
	<appender name="log.log" type="log4net.Appender.FileAppender">
		<file value=".\log.log" />
		<layout type="log4net.Layout.PatternLayout">
			<conversionPattern value="%date %message%newline" />
		</layout>
	</appender>
	<root>
		<level value="ALL" />
		<appender-ref ref="log.log" />
	</root>
</log4net>

When editing the config-file at run-time, you get:
log4net:ERROR [FileAppender] ErrorCode: GenericFailure. Unable to acquire lock on file ...\log.log. The process cannot access the file '...\log.log' because it is being used by another process.

Due the file-change, the appenders are getting re-configured.
v3.3.0 old appenders were stopped and removed before new appenders were created and added.
v3.3.1 new appenders are created before old appenders are stopped.
The old appender still has a lock on the file.
The new appender is created and calls ActivateOptions()->OpenFile().

point the npm changelog entry at its own pull request

close the outgoing appenders before activating the new ones #321

point the npm changelog entry at its own pull request

Confirmed, and your analysis is right: #287 (3.3.1) made the configurator activate the new appenders before swapping them in, so the incoming FileAppender opens the file while the outgoing one still holds it.

Fix is in #322. Could you build that branch and check it against your setup? That is the measurement we are missing. If building from source is awkward, say so and we will put up a preview package.

Two things so nothing surprises you:

close the outgoing appenders before activating the new ones #321 #322 looks far bigger than this fix. That is because it sits on top of file locking: keep the log on a failed roll, fix the mutex name #319, which is not merged yet. Only XmlHierarchyConfigurator.cs belongs to this issue.

I've built the 322 branch locally and tested it with my solution.
I can confirm that this fixes my error.

Thank you very much.
Looking forward for release 3.50.

@urs-hart

@urs-hart thanks for the feedback. I'm positive we can publish 3.5.0 by the end of September.

close the outgoing appenders before activating the new ones #321

point the npm changelog entry at its own pull request

discard an appender that fails to activate #321

close the outgoing appenders before activating the new ones #321 - #322

take npm dependencies from logging-parent gha/v0 apache#321

@urs-hart

@urs-hart we released https://github.com/apache/logging-log4net/releases/tag/rel%2F3.5.0

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File lock error when using FileAppender with XmlConfigurator.ConfigureAndWatch (v3.3.1) #321

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File lock error when using FileAppender with XmlConfigurator.ConfigureAndWatch (v3.3.1) #321

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FreeAndNil commented on Sep 19, 2026

urs-hart commented on Sep 21, 2026

FreeAndNil commented on Sep 21, 2026

FreeAndNil commented on Oct 1, 2026

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