Mal Graty created STORM-3163:
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Summary: ShellLogHandler setup should be done on the same thread
that uses it
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
`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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