Avoid Diags lock for syslog output#13398
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Syslog-only diagnostics take the same mutex used to serialize file output, adding avoidable contention when many threads report a shared failure. This limits the diagnostics mutex to FILE-backed destinations and removes the obsolete FreeBSD exception because syslog provides its own thread safety. Fixes: apache#7374
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Pull request overview
This PR reduces diagnostics-related lock contention by avoiding the Diags mutex when the configured destination is syslog-only. This aligns with ATS’s multi-threaded runtime characteristics where high fan-out warnings/notes can otherwise serialize on a shared lock.
Changes:
- Limits
Diags::print_va()locking to FILE-backed outputs (diagslog/stdout/stderr and regression stderr). - Removes the FreeBSD-specific “hold lock through syslog” exception so syslog is no longer serialized behind the diagnostics mutex.
- Minor refactor to use a single
outputreference for the selecteddiags_level.
JosiahWI
approved these changes
Jul 16, 2026
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Syslog-only diagnostics take the same mutex used to serialize file
output, adding avoidable contention when many threads report a shared
failure.
This limits the diagnostics mutex to FILE-backed destinations and
removes the obsolete FreeBSD exception because syslog provides its own
thread safety.
Fixes: #7374