[LOG4J2-1681] Introduce interfaces IndexedStringMap and IndexedReadOnlyStringMap

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.7
• Fix Version/s: 2.8
• Component/s: API
• Epic Link: GC-free
• Assignee: Remko Popma
• Reporter: Remko Popma
• Created: 08/Nov/16 11:49
• Updated: 20/Nov/16 12:08
• Resolved: 20/Nov/16 12:05

Description

This ticket proposes to introduce a public interface that imposes a total ordering over the keys of a (ReadOnly)StringMap. This interface views all key-value pairs as a sequence ordered by key, and allows keys and values to be accessed by their index in the sequence.

interface IndexedReadOnlyStringMap extends ReadOnlyStringMap {
    String getKeyAt(final int index);
    <V> V getValueAt(final int index);
    int indexOfKey(final String key);
}

interface IndexedStringMap extends IndexedReadOnlyStringMap, StringMap {}

The intention is to let SortedArrayStringMap implement these interfaces. (It already implements the necessary methods; the visibility of these methods will change from package-protected to public.)

These interfaces help reduce log4j's dependency on the JDK Map interface: the JDK Map interface does not provide a garbage-free way to iterate over all its keys or key-value pairs.

For example, these interfaces can be used to make MapFilter and its subclasses garbage-free, and reduce allocation of temporary objects in MapMessage and subclasses.

Issue Links

• is depended upon by: LOG4J2-1683 (GC) Avoid allocating temporary objects in MapMessage
• is depended upon by: LOG4J2-1677 (GC) Avoid allocating temporary objects in MapFilter
• is depended upon by: LOG4J2-1678 (GC) Avoid allocating temporary objects in ThreadContextMapFilter
• is depended upon by: LOG4J2-1679 (GC) Avoid allocating temporary objects in StructuredDataFilter
• supercedes: LOG4J2-1447 Garbage-free data structure for LogEvent's context map data