Fixed jni test and compile warnings

[luyuncheng]

Description

when i try to compile and test jni with main branch. i see the following error:

release/libopensearchknn_faiss.so: undefined reference to `_gfortran_compare_string'
release/libopensearchknn_faiss.so: undefined reference to `_gfortran_concat_string'

jni/tests/test_util.h:111:48: error: ‘idx_t’ is not a member of ‘faiss::Index’

i think this because faiss update to new branch,
so i pr this for fix the compile error:
faiss::Index::idx_t ==> faiss::idx_t
cmake add GFORTRAN_LIBRARY

ISSUE: #941

[navneet1v]

@luyuncheng Thanks for fixing the tests. This: GFORTRAN_LIBRARY, I am not sure what it is doing. Can you add some details why this is needed and what it is doing?

[navneet1v]

@luyuncheng please look at this: https://github.com/opensearch-project/k-NN/blob/main/CONTRIBUTING.md, I see few things missing like Developer Certificate, and add your change in CHANGELOG.md file too.

[codecov]

Codecov Report

Merging #940 (f3d0aa2) into main (a2ee834) will not change coverage.
The diff coverage is n/a.

❗ Current head f3d0aa2 differs from pull request most recent head c353126. Consider uploading reports for the commit c353126 to get more accurate results

@@            Coverage Diff            @@
##               main     #940   +/-   ##
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  Coverage     85.08%   85.08%           
  Complexity     1112     1112           
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  Files           152      152           
  Lines          4519     4519           
  Branches        405      405           
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  Hits           3845     3845           
  Misses          489      489           
  Partials        185      185           

[luyuncheng]

@luyuncheng Thanks for fixing the tests. This: GFORTRAN_LIBRARY, I am not sure what it is doing. Can you add some details why this is needed and what it is doing?

@navneet1v i think this because OpenBLAS using gfortrian with dynamic link, and in different platform, different version of gcc, would cause compiler throw exception without -lgfortran shows as followings:

release/libopensearchknn_faiss.so: undefined reference to `_gfortran_compare_string'
release/libopensearchknn_faiss.so: undefined reference to `_gfortran_concat_string'

[navneet1v]

@luyuncheng Thanks for fixing the tests. This: GFORTRAN_LIBRARY, I am not sure what it is doing. Can you add some details why this is needed and what it is doing?

@navneet1v i think this because OpenBLAS using gfortrian with dynamic link, and in different platform, different version of gcc, would cause compiler throw exception without -lgfortran shows as followings:

release/libopensearchknn_faiss.so: undefined reference to `_gfortran_compare_string'
release/libopensearchknn_faiss.so: undefined reference to `_gfortran_concat_string'

@luyuncheng is there any performance benefit of adding this? or this is just to resolve the compilation warnings?

[luyuncheng]

@luyuncheng is there any performance benefit of adding this? or this is just to resolve the compilation warnings?

@navneet1v Resolve compilation errors

it is because we install OpenBLAS with all package with brew install , and without 'make NO_LAPACK=1' ,
like cmake shows:

Found BLAS: /usr/lib/libopenblas.a;/usr/lib/gcc/x86_64-linux-gnu/6/libgomp.so;/usr/lib/x86_64-linux-gnu/libpthread.so;-lpthread

so we need link to lgfortran3. like this OpenBLAS isses 2287

[navneet1v]

can we put this like Fixed jni test and compile warnings, as if it would have been error the build should have faied.

[luyuncheng]

++ LGTM

[navneet1v]

@jmazanec15 can you take a look?

[jmazanec15]

do we need the version number?

[luyuncheng]

libgfortran has different version number for different GCC version.
like gcc 4.5.2 maps /usr/lib64/libgfortran.so.1
like gcc 6.2.0 gcc 5.x maps /usr/lib64/libgfortran.so.3
AND there is no soft link from libgfortran.so to libgfortran.so.3.0.0

So how about enum some version of libgfortran in find_library?