[smengcl]

Generated-by: Claude Code (Opus 5.5)

What changes were proposed in this pull request?

TestOMBootstrap#testBootstrapFollower timed out waiting for Install Checkpoint is finished in the OM log capture, although the follower OM had logged that line 30 seconds before the timeout.

Log4j1Capturer reused the layout instance of the root stdout appender. Log4j 1 PatternLayout is not thread-safe: format() resets and fills a single shared StringBuffer and relies on the owning appender's lock. Since the capture appender and stdout shared one layout, two threads could format into the same buffer at once, so a captured event could be replaced by, or mixed with, another event. The failing run shows the same race on the console, where two events from different threads were garbled into one line.

This affects any test using LogCapturer.captureLogs(...) while other threads log. The fix gives each capturer its own PatternLayout with the same conversion pattern, so each layout is only used under its own appender's lock.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-17209

How was this patch tested?

• Standalone repro (not committed): one thread logs 20000 marker lines to a captured logger while another thread logs to a different logger through stdout. With the original capturer, 58 markers were missing from the capture and text from the other logger leaked into it. With this patch, no markers were missing and nothing leaked.
• TestOMBootstrap locally: in progress
• 10x10 flaky-test-check on this branch: in progress

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