LightGBM Crash issue

[frank-dong-ms-zz]

lightgbm-org/LightGBM#2820

LightGBM has dependency on OpenMP multi-threading library. In our tests we are setting number of threads to be 1 for LightGBM and LightGBM also sets OpenMP to use only 1 thread. While OpenMP is also used by other native libraries and they also tend to set number of threads for OpenMP to use (by default this is number of cores, in our case it is 2 as we are using https://docs.microsoft.com/en-us/azure/virtual-machines/dv2-dsv2-series#dsv2-series). This setting(number of threads) is global in process and cause LightGBM referencing OpenMP from single threads to multi-threads. LightGBM is using number of threads for indexing and thus cause index out of range in native code and crash the process.

By this fix, we are not force single threading when run LightGBM related tests thus default behavior is applied and all the libraries use same number of threads for OpenMP.

Idealy LightGBM better not to rely number of threads to do indexing as this setting is global and likely be override by other library.

[harishsk]

    public void LightGBMBinaryEstimator()

Were these the crashing tests?
Weren't they disabled?

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Refers to: test/Microsoft.ML.Tests/TrainerEstimators/TreeEstimators.cs:51 in cf16c7d. [](commit_id = cf16c7d, deletion_comment = False)

[harishsk]

Can we add a detailed note somewhere in code visibly about why this is done?
Can we also add a cross reference to that comment wherever we have removed the NumberOfThreads = 1

[frank-dong-ms-zz]

Yes, I can add some comments with // Attention tags and put explain on comments

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In reply to: 388442580 [](ancestors = 388442580)

[frank-dong-ms-zz]

    public void LightGBMBinaryEstimator()

Yes, these are the crashing tests, they not disabled because I has check in a mitigation before (disable test parallelization). This time I have remove the mitigation that remove the AssemblyInfo.cs from ML.Tests assembly

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In reply to: 595344964 [](ancestors = 595344964)

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Refers to: test/Microsoft.ML.Tests/TrainerEstimators/TreeEstimators.cs:51 in cf16c7d. [](commit_id = cf16c7d, deletion_comment = False)

[harishsk]