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https://issues.apache.org/jira/browse/STORM-3163?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mal Graty closed STORM-3163.
----------------------------
Resolution: Not A Problem
Turns out that this is much better solved by leveraging \{{log4j2}}'s
\{{isThreadContextMapInheritable}} property, which hands child threads a
point-in-time copy of the parent's \{{MDC}} contents, which completely solves
the issue this sought to address.
> ShellLogHandler loses thread context between setup and use
> ----------------------------------------------------------
>
> Key: STORM-3163
> URL: https://issues.apache.org/jira/browse/STORM-3163
> Project: Apache Storm
> Issue Type: Bug
> Components: storm-core
> Affects Versions: 1.2.2
> Reporter: Mal Graty
> Priority: Trivial
> Labels: Logging, pull-request-available
> Time Spent: 20m
> Remaining Estimate: 0h
>
> *UPDATE*
> Turns out that this is much better solved by leveraging {{log4j2}}'s
> {{isThreadContextMapInheritable}} property, which hands child threads a
> point-in-time copy of the parent's {{MDC}} contents, which completely solves
> the issue this sought to address.
> ---
> *ORIGINAL*
> tl;dr: {{ShellLogHandler}} is handed context in one thread, before being used
> exclusively from another, this obstructs sane usage of {{slf4j}}'s {{MDC}}
> feature which is thread local.
> ---
> {{ShellBolt}} instantiates the {{ShellLogHandler}} and calls its
> {{setUpContext}} as part of {{prepare}}, immediately before it spawns its
> {{BoltReaderRunnable}} and {{BoltWriterRunnable}} threads which are
> responsible for communication with the {{ShellProcess}} that's already been
> spawned.
> The {{ShellLogHandler}} is used exclusively from {{BoltReaderRunnable}}. The
> upshot of this is that {{setUpContext}} is executed in the task thread (i.e.
> {{Thread-21-joiner-executor[2 2]}}) while the {{log}} method is executed in
> the anonymous thread (i.e. {{Thread-30}}) running the {{BoltReaderRunnable}}.
> This creates a problem when trying to leverage {{slf4j}}'s {{MDC}} (or
> {{NDC}}) which are used for augmenting log messages with additional
> information which is localised and persisted at the thread level.
> The current work around for this is to store all relevant context on the
> {{ShellLogHandler}} during {{setUpContext}}, and then write it into the
> {{MDC}} during the {{log}} call, and taking precautions around that state
> being thread safe. The thread safety requirement is the first drawback, the
> second is that each {{log}} call has the additional overhead of either
> unconditionally writing to the {{MDC}} or checking that the {{MDC}} is
> already populated. Neither is very appealing.
> The suggested solution is to pass {{stormConf}}, {{_process}}, and
> {{_context}} into the constructor of {{BoltReaderRunnable}} (and perhaps also
> {{BoltWriterRunnable}}) and instantiate {{ShellLogHandler}} and call its
> {{setUpContext}} from that thread.
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