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https://issues.apache.org/jira/browse/LOG4J2-1349?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15451989#comment-15451989
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Remko Popma commented on LOG4J2-1349:
-------------------------------------
Yes, these are the selected implementations that will all be used in production
usage. The OpenHashMap implementations (used in the benchmarks) have been moved
to log4j-perf.
The remaining implementations will be used as follows:
* GarbageFreeSortedArrayThreadContextMap - if the user configured GC-free
context map
* CopyOnWriteSortedArrayThreadContextMap - the default for non-web app
applications
* DefaultThreadContextMap - the default for web applications (or when
Constants.ENABLE_THREADLOCALS is false)
I'm not sure if it is possible to move ArrayContextData to core since it is
used to implement two of the above context maps. What would be the benefit?
Currently the SPI package is self-contained and doesn't depend on core. That
seems like a good thing. Not sure what the problem is...
> Garbage-free ThreadContext map
> ------------------------------
>
> Key: LOG4J2-1349
> URL: https://issues.apache.org/jira/browse/LOG4J2-1349
> Project: Log4j 2
> Issue Type: Improvement
> Components: API
> Affects Versions: 2.5
> Reporter: Remko Popma
> Assignee: Remko Popma
> Fix For: 2.7
>
> Attachments: DataStructOpsPerfMediumDataSet.png,
> DataStructOpsPerfSmallDataSet.png, InjectWithConfigProperties.png,
> InjectWithoutConfigProperties.png, ThreadContextPut.png,
> v2_DataStructOpsPerfMediumDataSet.png, v2_DataStructOpsPerfSmallDataSet.png,
> v2_InjectWithConfigProperties.png, v2_InjectWithoutConfigProperties.png,
> v2_ThreadContextGet.png, v2_ThreadContextPut.png
>
>
> The current ThreadContext map and stack implementations allocate temporary
> objects. This ticket is to investigate and track the work for alternative
> implementations that are garbage-free.
> Both DefaultThreadContextMap and DefaultThreadContextStack are copy-on-write
> data structures: each modification replaces the ThreadLocal object with a
> modified copy. The advantage of this approach is that there is no need to
> make a copy for each LogEvent.
> Also, DefaultThreadContextMap uses a JDK map, the JDK collections tend to
> allocate a lot of temporary objects.
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