[R] Don't cap global number of threads for serialization (#10028)

R-package/R/xgb.DMatrix.save.R

@@ -6,6 +6,7 @@
 #' @param fname the name of the file to write.
 #'
 #' @examples
+#' \dontshow{RhpcBLASctl::omp_set_num_threads(1)}
 #' data(agaricus.train, package='xgboost')
 #' dtrain <- with(agaricus.train, xgb.DMatrix(data, label = label, nthread = 2))
 #' fname <- file.path(tempdir(), "xgb.DMatrix.data")

R-package/R/xgb.config.R

@@ -4,7 +4,14 @@
 #' values of one or more global-scope parameters. Use \code{xgb.get.config} to fetch the current
 #' values of all global-scope parameters (listed in
 #' \url{https://xgboost.readthedocs.io/en/stable/parameter.html}).
+#' @details
+#' Note that serialization-related functions might use a globally-configured number of threads,
+#' which is managed by the system's OpenMP (OMP) configuration instead. Typically, XGBoost methods
+#' accept an `nthreads` parameter, but some methods like `readRDS` might get executed before such
+#' parameter can be supplied.
 #'
+#' The number of OMP threads can in turn be configured for example through an environment variable
+#' `OMP_NUM_THREADS` (needs to be set before R is started), or through `RhpcBLASctl::omp_set_num_threads`.
 #' @rdname xgbConfig
 #' @title Set and get global configuration
 #' @name xgb.set.config, xgb.get.config

R-package/R/xgb.dump.R

@@ -24,6 +24,7 @@
 #' as a \code{character} vector. Otherwise it will return \code{TRUE}.
 #'
 #' @examples
+#' \dontshow{RhpcBLASctl::omp_set_num_threads(1)}
 #' data(agaricus.train, package='xgboost')
 #' data(agaricus.test, package='xgboost')
 #' train <- agaricus.train

R-package/R/xgb.load.R

@@ -20,6 +20,7 @@
 #' \code{\link{xgb.save}}
 #'
 #' @examples
+#' \dontshow{RhpcBLASctl::omp_set_num_threads(1)}
 #' data(agaricus.train, package='xgboost')
 #' data(agaricus.test, package='xgboost')
 #'

R-package/R/xgb.save.R

@@ -35,6 +35,7 @@
 #' \code{\link{xgb.load}}
 #'
 #' @examples
+#' \dontshow{RhpcBLASctl::omp_set_num_threads(1)}
 #' data(agaricus.train, package='xgboost')
 #' data(agaricus.test, package='xgboost')
 #'

R-package/R/xgb.save.raw.R

@@ -12,6 +12,7 @@
 #' }
 #'
 #' @examples
+#' \dontshow{RhpcBLASctl::omp_set_num_threads(1)}
 #' data(agaricus.train, package='xgboost')
 #' data(agaricus.test, package='xgboost')
 #'