Github user vanzin commented on the pull request:
https://github.com/apache/spark/pull/1031#issuecomment-57518693
I wrote a small test for this; it uses three implementations of the same
native library that print different things, and a small java class to call it.
This is the output:
LD_LIBRARY_PATH=lib1
ld1
java.library.path=lib2
ld2
LD_LIBRARY_PATH=lib1 and java.library.path=lib2
ld2
LD_LIBRARY_PATH=lib1 and invalid java.library.path
Exception in thread "main" java.lang.UnsatisfiedLinkError: no javald in
java.library.path
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1857)
at java.lang.Runtime.loadLibrary0(Runtime.java:870)
at java.lang.System.loadLibrary(System.java:1119)
at ld.main(ld.java:4)
lib3 in /usr/lib and LD_LIBRARY_PATH=lib1 and java.library.path=lib2
ld2
lib3 in /usr/lib and LD_LIBRARY_PATH=lib1
ld1
lib3 in /usr/lib and java.library.path=lib2
ld2
lib3 in /usr/lib and invalid LD_LIBRARY_PATH
ld3
lib3 in /usr/lib and invalid java.library.path
Exception in thread "main" java.lang.UnsatisfiedLinkError: no javald in
java.library.path
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1857)
at java.lang.Runtime.loadLibrary0(Runtime.java:870)
at java.lang.System.loadLibrary(System.java:1119)
at ld.main(ld.java:4)
So Tom's observation that setting `java.library.path` prevents the JVM from
looking for libraries in the system path (or `LD_LIBRARY_PATH`) seems correct.
So, basically, relying on `java.library.path` means that anyone trying to use
JNI libs in system directories will have a hard time doing so.
So, perhaps, even if it's more code, using `LD_LIBRARY_PATH` would result
in more intuitive behavior for users.
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