fix: Prevent LogBuilder memory leak in Log4j API to Logback bridge
#3824
+103
−7
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This change fixes a potential memory leak in the `log4j-to-slf4j` module (Log4j API to Logback bridge) caused by the use of a thread-local `LogBuilder` pool. The leak occurred because the thread-local field was accessed, even when `log4j2.enableThreadlocals` was set to `false`. In servlet environments, this could lead to classloader leaks due to the persistence of thread-local references. With this fix, all access to the `ThreadLocal` is now **properly** gated by the `log4j2.enableThreadlocals` system property—matching how similar pooling behavior is handled in Log4j Core. This preserves the GC-free option for advanced users who explicitly opt in via `log4j2.enableThreadlocals = true`, while avoiding memory leaks for others. Fixes #3819
The `--add-opens` JVM option is now included in a dedicated Maven profile to avoid applying it during CI builds on JRE 8, where it is unsupported and unnecessary.
gmiscione
approved these changes
Jul 14, 2025
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This change fixes a potential memory leak in the
log4j-to-slf4jmodule (Logback Log4j API binding) caused by the use of a thread-localLogBuilderpool.The leak occurred because the thread-local field was accidentally accessed, even when
log4j2.enableThreadlocalswas set tofalse. In servlet environments, this could lead to classloader leaks due to the persistence of thread-local references.With this fix, all access to the
ThreadLocalis now properly gated by thelog4j2.enableThreadlocalssystem property—matching how similar pooling behavior is handled in Log4j Core.This preserves the GC-free option for advanced users who explicitly opt in via
log4j2.enableThreadlocals = true, while avoiding memory leaks for others.Fixes #3819