The `immediateFlush` option in both rolling file appenders is ignored

[jvz]

Description

Both the RollingFileAppender and RollingRandomAccessFileAppender plugins offer a boolean flag, immediateFlush, to allow for immediate flushing of buffers when writing data. This option is ultimately discarded when creating the corresponding RollingFileManager and RollingRandomAccessFileManager instances.

Configuration

Version: 2.x and main

Operating system: all

JDK: all

Logs

n/a

Reproduction

The amusing part is that we have tons of tests that set immediateFlush to true or false, yet none of these tests verify that it does anything.

[ppkarwasz]

The property is used in AbstractOutputStreamAppender#directEncodeEvent and AbstractOutputStreamAppender#writeByteArrayToManager. As far as I can tell, it is not ignored.

[jvz]

Which is why static analysis is complaining about what exactly?

[ppkarwasz]

The SAST tool is right: RollingFileManager doesn't do anything with the property, but RollingFileAppender does.

It would be useful to remove the property from RollingFileManager since it is not used.

[jvz]

Oh, then consider this a bug for that. Unused fields are a bug.

[tcmot]

Hi,

RandomAccessFile 

FileChannel channel = randomAccessFile.getChannel();
randomAccessFile.write();
channel.force(true);

Use the force method，the file be updated in real time. But affects performance.
Log4j2，not use the force method.

Rewrite RollingRandomAccessFileManager and RandomAccessFileManager flush method. Add the code above.

[ppkarwasz]

@jvz,

I investigated the effects of flush() on the FileAppender a little bit further and it is a no-op in FileOutputStream (the output stream does not use any Java buffers, so there is nothing to flush). So I would propose to:

• remove immediateFlush from FileAppender.Builder and similar,
• remove any references to immediateFlush in the documentation.

[jvz]

@ppkarwasz sounds like a good idea to me!

[ppkarwasz]

Actually there is another usage of immediateFlush: resource managers use a ByteBuffer to format each log event.

If immediateFlush is true, the byte buffer is flushed at each event.