feat: set blas threads to 1

R/worker.R

@@ -268,6 +268,16 @@ workhorse = function(iteration, task, learner, resampling, param_values = NULL,
       old_blas_threads = RhpcBLASctl::blas_get_num_procs()
       on.exit(RhpcBLASctl::blas_set_num_threads(old_blas_threads), add = TRUE)
       RhpcBLASctl::blas_set_num_threads(1)
+    } else { # try the bare minimum to disable threading of the most popular blas implementations
+      old_blas = Sys.getenv("OPENBLAS_NUM_THREADS")
+      old_mkl = Sys.getenv("MKL_NUM_THREADS")
+      Sys.setenv(OPENBLAS_NUM_THREADS = 1)
+      Sys.setenv(MKL_NUM_THREADS = 1)
+
+      on.exit({
+        Sys.setenv(OPENBLAS_NUM_THREADS = old_blas)
+        Sys.setenv(MKL_NUM_THREADS = old_mkl)
+      }, add = TRUE)
     }
   }
   # restore logger thresholds

man-roxygen/section_parallelization.R

@@ -4,3 +4,5 @@
 #' One job is one resampling iteration, and all jobs are send to an apply function
 #' from \CRANpkg{future.apply} in a single batch.
 #' To select a parallel backend, use [future::plan()].
+#' More on parallelization can be found in the book:
+#' \url{https://mlr3book.mlr-org.com/chapters/chapter10/advanced_technical_aspects_of_mlr3.html}