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fix(log): serialize writes to an IO logger so lines from several threads don't mix on JRuby - #683
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…ads don't mix on JRuby CDP messages are logged from the caller or writer thread when sent and from the WebSocket reader thread when received, browser output from the process output thread. On JRuby, without a GVL, concurrent StringIO#puts calls interleave and corrupt lines. Logger instances already synchronize, so only the puts path is locked.
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On JRuby,
spec/browser_spec.rb:149(FERRUM_LOG_FORMAT=json) failed with a line that held two CDP messages mixed together (run).Log#writecallslogger.putsfrom several threads:sentfrom the caller or writer thread,receivedfrom each WebSocket reader thread,browserfrom the process output thread. MRI's GVL makesStringIO#putseffectively atomic, JRuby has no GVL, so concurrent writes interleave and corrupt lines.The line is now built outside a mutex and only
putsruns inside it. ALoggeralready synchronizes itself, so that path is unchanged. The new unit spec fails on JRuby without the fix.