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https://issues.apache.org/jira/browse/HAWQ-1210?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15742603#comment-15742603
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William Forson commented on HAWQ-1210:
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Hi Zhanwei Wang,
Unfortunately, I don't think I will have the bandwidth to debug this further
for at least a few weeks. So far, I've been using libhdfs3 as a black-box
component (i.e. I've really only looked at {{hdfs.h}} and build logic), so I
will have to get myself up to speed on the basic organization of the codebase,
etc.
However, since there is a decent chance I will be using libhdfs3 as a
production dependency, in a multi-threaded environment, I would definitely like
to understand what is going on here. So I will try to look into this as soon as
I have the time.
Thanks!
> Documentation regarding usage of libhdfs3 in concurrent environment
> -------------------------------------------------------------------
>
> Key: HAWQ-1210
> URL: https://issues.apache.org/jira/browse/HAWQ-1210
> Project: Apache HAWQ
> Issue Type: Bug
> Components: libhdfs
> Reporter: William Forson
> Assignee: Lei Chang
> Attachments: hdfs_fs_concurrent_test.cpp
>
>
> Hi,
> I've been using libhdfs3 in a single-threaded environment for several months
> now, without any problems. However, as soon as I tried using the library
> concurrently from multiple threads: hello, segfaults.
> Although the source of these segfaults is annoyingly subtle, I've managed to
> isolate it to a relatively small block of my code that does nothing
> interesting aside from using libhdfs3 to download a single hdfs file.
> To be clear: I assume that the mistake here is mine -- that is, that I am
> using your library incorrectly. However, I have been unable to find any
> documentation as to how the libhdfs3 API _should_ be used in a multi-threaded
> environment. I initially interpreted this to mean, "go to town, it's all more
> or less thread-safe", but I am now questioning that interpretation.
> So, I have a question, and a request.
> Question: Are there any known, non-obvious concurrency gotchas regarding the
> usage of libhdfs3 (or whatever it's currently called)?
> Request: Could you please add some documentation, to the README and/or
> hdfs.h, regarding usage in a concurrent environment? (ideally, such notes
> would annotate individual components of the API in hdfs.h, but if the answer
> to my question above is, "No", then this could perhaps be a single sentence
> in the README which affirmatively states that the library is generally safe
> for concurrent usage without additional/explicit synchronization -- anything
> would be better than nothing :))
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