fix: reduce number of threads to 1 on rush worker (#281)

Author: be-marc

DESCRIPTION

@@ -43,6 +43,7 @@ Suggests:
     progressr,
     processx,
     redux,
+    RhpcBLASctl,
     testthat (>= 3.0.0),
     rush (>= 0.1.2)
 Remotes:

R/worker_loops.R

@@ -17,6 +17,28 @@ bbotk_worker_loop = function(rush, optimizer, instance) {
   instance$rush = rush
   instance$archive$rush = rush
 
+  # reduce number of threads to 1
+  old_dt = data.table::getDTthreads()
+  on.exit(data.table::setDTthreads(old_dt), add = TRUE)
+  data.table::setDTthreads(1, restore_after_fork = TRUE)
+
+  # RhpcBLASctl is licensed under AGPL and therefore should be in suggest
+  if (require_namespaces("RhpcBLASctl", quietly = TRUE)) {
+    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)
+  }
+
   call_back("on_worker_begin", instance$objective$callbacks, instance$objective$context)
 
   # run optimizer loop