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https://issues.apache.org/jira/browse/HTRACE-119?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14341937#comment-14341937
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Colin Patrick McCabe edited comment on HTRACE-119 at 3/2/15 7:27 PM:
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Hi [~iwasakims],
Thanks for explaining that! I feel silly now. You are right that the way
htrace is handling {{NullScope}} is incorrect right now. By handing out the
same {{NullScope}} instance to everyone, and only allowing detach once on that
singleton, we are making correct user code fail.
I wonder if, rather than changing the code path in {{TraceScope}}, we could
just add a {{NullScope#detach}} function that does nothing (and returns null).
It seems like this would fix the problem, while not allowing double detach when
tracing was on. \[edit: actually patch 001 does not allow double detach in the
non-NullScope case... see below\] There is still an issue with us not catching
double detach when {{NullScope}} is in use, but perhaps the optimization of
avoiding creating a new scope when tracing is off outweighs that concern?
Take a look at HTRACE-119-002.patch...
was (Author: cmccabe):
Hi [~iwasakims],
Thanks for explaining that! I feel silly now. You are right that the way
htrace is handling {{NullScope}} is incorrect right now. By handing out the
same {{NullScope}} instance to everyone, and only allowing detach once on that
singleton, we are making correct user code fail.
I wonder if, rather than changing the code path in {{TraceScope}}, we could
just add a {{NullScope#detach}} function that does nothing (and returns null).
It seems like this would fix the problem, while not allowing double detach when
tracing was on. There is still an issue with us not catching double detach
when {{NullScope}} is in use, but perhaps the optimization of avoiding creating
a new scope when tracing is off outweighs that concern?
Take a look at HTRACE-119-002.patch...
> detach of NullScope singleton should not fail
> ---------------------------------------------
>
> Key: HTRACE-119
> URL: https://issues.apache.org/jira/browse/HTRACE-119
> Project: HTrace
> Issue Type: Bug
> Affects Versions: master
> Reporter: Masatake Iwasaki
> Assignee: Masatake Iwasaki
> Attachments: HTRACE-119.001.patch, HTRACE-119.002.patch,
> HTRACE-119.003.patch
>
>
> The {{detach}} method of NullScope singleton is possible to be called
> multiple times by users avoiding conditionals by the assumption that
> NullScope#close and NullScope#detach results in no-op. Calling {{detach}} of
> NullScope singleton multiple times throws RuntimeException by HTRACE-101 now.
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