[LOG4J2-1447] Garbage-free data structure for LogEvent's context map data

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.6.1
• Fix Version/s: 2.7
• Component/s: Core
• Epic Link: GC-free
• Assignee: Remko Popma
• Reporter: Remko Popma
• Created: 24/Jun/16 00:21
• Updated: 20/Nov/16 12:08
• Resolved: 11/Sep/16 06:56

Description

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.

Issue Links

• is depended upon by: LOG4J2-1401 Support changing the log level for all messages related to some domain object
• is depended upon by: LOG4J2-1010 Injectable context properties
• is related to: LOG4J2-1648 Allow non-String values in the ThreadContext
• is related to: LOG4J2-1349 Garbage-free ThreadContext map
• is related to: LOG4J2-1607 Improve performance of SortedArrayStringMap data structure
• is superceded by: LOG4J2-1681 Introduce interfaces IndexedStringMap and IndexedReadOnlyStringMap
• relates to: LOG4J2-1516 Add ThreadContextMap.putAll(Map<String, String>)
• relates to: LOG4J2-1517 Add ThreadContext.setContext(Map<String, String>)
• relates to: LOG4J2-1519 Add ThreadContext.putAll(Map<String, String>)