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From "Remko Popma (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LOG4J2-1447) Garbage-free data structure for LogEvent's context map data
Date Tue, 23 Aug 2016 15:34:21 GMT

    [ https://issues.apache.org/jira/browse/LOG4J2-1447?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15433027#comment-15433027

Remko Popma commented on LOG4J2-1447:

No, one implementation is enough. After the most recent set of benchmark results in LOG4J2-1349
my conclusion is that ArrayContextData gives the best trade-off. After review, when merging
this into master, if there are no objections I will move the OpenHashContextData implementation
to elsewhere (either src/test or to the log4j-perf module).

Yes, we do still need ContextDataFactory to allow users to specify custom ContextData implementations.
At work I have a use case for putting primitive values in the context data (LOG4J2-1401).
This is too domain-specific to push into log4j, but having ContextDataFactory makes it possible
for me to accomplish this without impacting log4j.

> Garbage-free data structure for LogEvent's context map data
> -----------------------------------------------------------
>                 Key: LOG4J2-1447
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-1447
>             Project: Log4j 2
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 2.6.1
>            Reporter: Remko Popma
>            Assignee: Remko Popma
>             Fix For: 2.7
> With each logging call, context map data is copied from the {{ThreadContext}} map into
the {{LogEvent}}.
> The LogEvent interface exposes this data via the {{getContextMap() : Map<String, String>}}
method, and this is implementated by storing the data in a Map<String, String>.  The
JDK Map is not an easy data structure to make garbage-free. It would also be nice to have
the ability in LogEvent to carry data of any type.
> One idea is to introduce a small interface that is general enough to be map-like but
can be implemented in a garbage-free manner. 
> LogEvent implementations would have an instance of this interface instead of the current
{{java.util.Map<String, String> contextMap}} attribute.
> The interface could look something like this:
> {code}
> interface ContextData<String, V> {
>     /** Called to implement {@link LogEvent#getContextMap()}. */
>     Map<String, String> asMap();
>     /** Put key-value pair into the table.
>         Remove key if value is null. */
>     void put(String key, V value);
>     /** Returns the value for the specified key. */
>     V getValue(String key);
>     /** Number of key-value pairs. */
>     int size();
>     /** Removes all key-value pairs. */
>     void clear();
> // Instead of Iterators, client code provides the consumer.
>     /** 
>      * Performs the given action for each key-value pair in this data structure
>      * until all entries have been processed or the action throws an exception.
>      */
>     void forEach(BiConsumer<String, ? super V> action);
> }
> /**
>  * An operation that accepts two input arguments and returns no result.
>  */
> interface BiConsumer<T,U> {
>     /** Performs the operation given the specified arguments. */
>     void accept(T t, U u);
> }
> {code}
> The LogEvent interface would have an additional method {{getContextData() : ContextData<K,
V>}} that gives downstream components direct access to the new data structure. 
> Existing downstream components would still be able to call {{logEvent.getContextMap()}}
to get a {{Map<String, String>}} view of the context map data and this would work as

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