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  1. Log4j 2
  2. LOG4J2-1447

Garbage-free data structure for LogEvent's context map data



    • Improvement
    • Status: Closed
    • Major
    • Resolution: Fixed
    • 2.6.1
    • 2.7
    • Core
    • None


      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:

      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);

      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 expected.


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              rpopma Remko Popma
              rpopma Remko Popma
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