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https://issues.apache.org/jira/browse/HADOOP-8806?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13456529#comment-13456529
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Colin Patrick McCabe commented on HADOOP-8806:
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bq. On the downside, setting DT_RPATH=$ORIGIN on libhadoop.so pollutes the
search path for later dlopens in the main executable. In my test:
{code}
main.c
-> dlopens /path/to/libbar.so with DT_RPATH=$ORIGIN
-> dlopens libfoo.so
-> dlopens libfoo.so
{code}
I'm afraid you have been misled.
At the point when you are dlopening libfoo.so a second time, it is already
linked to the executable. Essentially, the dynamic linker realizes that you
already have libfoo loaded, and doesn't try to reload it a second time.
This behavior is sort of hinted at in the man page for dlopen, although it's
not spelled out explicitly. See the documentation for {{RTLD_NOLOAD}}, for
example. According to the man page, "This can be used to test if the library
is already resident." To me, this implies that:
* libraries can be either resident or not
* libraries can't be loaded twice in the same executable
Although those stipulations aren't spelled out explicitly. (Time to submit a
patch?)
Here's a modification of your test program which illustrates what I mean.
Basically it does:
{code}
main.c
-> dlopens /path/to/libbar.so with DT_RPATH=$ORIGIN
-> dlopens libfoo.so
-> dlopens libbaz.so
{code}
The last dlopen fails because {{libbaz.so}} is not in the library search path
(although it would succeed for {{libfoo.so}} opening it, due to {{RPATH}}.)
> libhadoop.so: dlopen should be better at locating libsnappy.so, etc.
> --------------------------------------------------------------------
>
> Key: HADOOP-8806
> URL: https://issues.apache.org/jira/browse/HADOOP-8806
> Project: Hadoop Common
> Issue Type: Improvement
> Reporter: Colin Patrick McCabe
> Assignee: Colin Patrick McCabe
> Priority: Minor
> Attachments: HADOOP-8806.003.patch, rpathtest2.tar.gz,
> rpathtest.tar.gz
>
>
> libhadoop calls {{dlopen}} to load {{libsnappy.so}} and {{libz.so}}. These
> libraries can be bundled in the {{$HADOOP_ROOT/lib/native}} directory. For
> example, the {{-Dbundle.snappy}} build option copies {{libsnappy.so}} to this
> directory. However, snappy can't be loaded from this directory unless
> {{LD_LIBRARY_PATH}} is set to include this directory.
> Can we make this configuration "just work" without needing to rely on
> {{LD_LIBRARY_PATH}}?
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