eval_safe not returning on R 4.2 for xgboost model predictions

[Helbrax]

I've recently upgraded a linux container to use R 4.2.1 and upgraded unix r package to 1.5.5 from 1.5.4.

I noticed after doing so, that certain requests were timing out/never completing. Upon further investigation, it looks like the code is no longer returning when being run under eval_safe. So far, I think I've narrowed it down to the "predict" method when called on an xgboost model.

Old session Info
`R version 4.1.1 (2021-08-10) -- xgboost here is 1.5.0.2
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 20.04.3 LTS

Matrix products: default
BLAS: /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.9.0
LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.9.0

locale:
[1] LC_CTYPE=C.UTF-8 LC_NUMERIC=C LC_TIME=C.UTF-8
[4] LC_COLLATE=C.UTF-8 LC_MONETARY=C.UTF-8 LC_MESSAGES=C
[7] LC_PAPER=C LC_NAME=C LC_ADDRESS=C
[10] LC_TELEPHONE=C LC_MEASUREMENT=C LC_IDENTIFICATION=C

attached base packages:
[1] stats graphics grDevices utils datasets methods base `

New session info
`R version 4.2.1 (2022-06-23) -- xgboost here is 1.6.0.1
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 20.04.5 LTS

Matrix products: default
BLAS: /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.9.0
LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.9.0

locale:
[1] C

attached base packages:
[1] stats graphics grDevices utils datasets methods base`

R results
`> predict(m, x, outputmargin=TRUE)
[1] -1.160798

unix::eval_safe(predict(m, x, outputmargin=TRUE))
^C
^C
Error in tryCatch({ : process interrupted by parent
unix::eval_safe(paste0("foo", "bar"))
[1] "foobar"
`

[Helbrax]

Quick update on this. If OMP_NUM_THREADS is set to 1, eval_safe runs fine. It's only when OMP_NUM_THREADS is not set and the predict model is running on all available cpu.
I've tried this at 8 vcpu with OMP_NUM_THREADS set to 1 and had no issue but leaving it unset caused eval_safe to hang. Setting the vcpu down to 1 and leaving OMP_NUM_THREADS unset also had no issue. This seems to be only when multi-cores are used.
Not sure if the issue is with eval_safe or some new threading issue with predict xgboost modeling using multiple cores.

[jeroen]

Can you include a complete reproducible example? Including an example model and x

[Helbrax]

See below.

library(xgboost)
library(unix)

data(agaricus.train, package='xgboost')
data(agaricus.test, package='xgboost')
train <- agaricus.train
test <- agaricus.test
dtrain <- xgb.DMatrix(data = train$data, label = train$label)
bst <- xgboost(data = dtrain, max.depth = 2, eta = 1, nthread = 2, nrounds = 2, objective = "binary:logistic", verbose = 0)
x <- predict(bst, test$data) # this complets
eval_safe(predict(bst, test$data)) # this hangs. if you change nthread=2 to nthead=1 in the training, it completes, OR load the model in and set OMP_NUM_THREADS=1 in environment variables