[LOG4J2-2533] Garbage creation introduced by LOG4J2-2301

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.11.1
• Fix Version/s: 3.0.0, 2.11.2
• Component/s: Core
• Assignee: Carter Kozak
• Reporter: Carter Kozak
• Created: 14/Jan/19 22:51
• Updated: 14/Jan/19 23:05
• Resolved: 14/Jan/19 23:04

Description

Reported here: https://github.com/apache/logging-log4j2/pull/251

Stack Trace TLABs Total TLAB Size(bytes) Pressure(%)
java.lang.ThreadLocal$ThreadLocalMap.set(ThreadLocal, Object) line: 481 10 3,638,864 56.192
java.lang.ThreadLocal$ThreadLocalMap.access$100(ThreadLocal$ThreadLocalMap, ThreadLocal, Object) line: 298 10 3,638,864 56.192
java.lang.ThreadLocal.setInitialValue() line: 184 10 3,638,864 56.192
java.lang.ThreadLocal.get() line: 170 10 3,638,864 56.192
org.apache.logging.log4j.core.async.AsyncLoggerConfig.log(LogEvent, LoggerConfig$LoggerConfigPredicate) line: 91 10 3,638,864 56.192

We clear and re-set a threadlocal value, which plays with the internal thread-map size like an accordion, increasing probability unused thread entries will be removed. By setting back to a default value rather than clearing the threadlocal we can avoid allocation.