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https://issues.apache.org/jira/browse/LOG4J2-1270?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15149594#comment-15149594
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Ralph Goers commented on LOG4J2-1270:
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Actually, it occurs to me that you can't use a ThreadLocal for the Message
because you can't then pass it off to another thread, so you would have to use
some sort of ring buffer that allows new Messages to be allocated should the
ring buffer be full.
> Garbage-free steady-state logging
> ---------------------------------
>
> Key: LOG4J2-1270
> URL: https://issues.apache.org/jira/browse/LOG4J2-1270
> Project: Log4j 2
> Issue Type: Epic
> Components: API, Appenders, Core, Layouts, Pattern Converters
> Affects Versions: 2.5
> Reporter: Remko Popma
> Labels: gc
>
> In certain fields like finance, predictable latency is very important, and
> applications in this space tend to carefully manage their object allocation
> to avoid unpredictable GC pauses. As of 2.5, Log4j is not suitable to be
> included in such applications since it allocates new objects while running in
> its steady state.
> This ticket is to investigate the feasibility of modifying some key
> components in Log4j to provide a configuration that does not allocate new
> objects in its steady state. (Initialization or shutdown don't need to be
> allocation-free.)
> To clarify, I am not proposing to make all of Log4j allocation-free. My goal
> is to create an allocation-free execution path in Log4j with some reasonable
> subset of the Log4j functionality. For example, make logging garbage-free if
> all of these conditions are met:
> * all loggers are AsyncLoggers
> * you only use the RandomAccessFileAppender
> * you only use a PatternLayout without any regular expression replacements,
> without lookups and with one of the pre-defined date formats.
> Further restrictions may be necessary.
> AsyncLogger already has a ring buffer of pre-allocated LogEvents, so some of
> the work here is already done.
> Components that currently allocate objects in the critical path:
> # (API) Logger methods with vararg parameters
> # (API) All MessageFactory implementations
> # LoggerConfig.getProperties (if non-null) - wraps in
> Collections.unmodifiableMap
> # RingBufferLogEvent.mergePropertiesIntoContextMap (if LoggerConfig
> properties is non-null)
> # LoggerConfig.callAppenders (for-each loop over CopyOnWriteArraySet creates
> iterator)
> # Layout.toByteArray(LogEvent) - this API makes it difficult to avoid
> allocating a new byte[] array for each log event
> # AbstractStringLayout.toByteArray() - turns each LogEvent into a new String
> before turning the String into a byte[] array
> # DatePatternConverter - new CachedTime if event.millis differs from previous
> event
> # DatePatternConverter.CachedTime - new String caching the result
> # FixedDateFormat - new char[] array
> # (FastDateFormat - for each event: new GregorianCalendar, new StringBuilder,
> new char[], new String)
> # String.getBytes - creates initial byte array, CharBuffer, ByteBuffer,
> trimmed resulting byte array
> The Layout API and turning Strings into bytes are probably the most tricky
> areas. One advantage of restricting ourselves to async logging is that there
> is only a single background thread that does all the formatting and I/O, so
> we don't have to worry about concurrency issues when re-using buffers etc.
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