Dead2 commented on issue #1775: Deadlock in shm statistics URL: https://github.com/apache/incubator-pagespeed-mod/issues/1775#issuecomment-394678320 We do not have a snapshot of the logs from this deadlock unfortunately. We did consider turning statistics off completely, but that would cause ImageMaxRewritesAtOnce to be ignored and potentially turn into a DOS attack vector. I do wish there was a setting for disabling all "fluff" statistics, only keeping the few things needed for communication between processes. Investigating this also made me wonder why ImageMaxRewritesAtOnce is global while NumRewriteThreads and NumExpensiveRewriteThreads are process-local (so global if using a threaded apache and per-connection if using prefork). So this might be something worth changing long-term too. But I am confused, the documentation says NumRewriteThreads and NumExpensiveRewriteThreads are per-process, so those should not be able to cause a deadlock across processes. And ImageMaxRewritesAtOnce is global, so it could cause this, but two of the processes above are trying to rewrite .css files and should thus not be affected. So, either I am missing something or the documentation is misleading, probably the former. :) We will try out your patch, but proving the problem is fixed can take a while, since it can take weeks to trigger the bug (sometimes twice in a few days, sometimes once in a month, so it seems very random).
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