Merge pull request #78 from aitap/openmp_fixes

Fixes for OpenMP limit options and detection

R/zzz.R

@@ -9,22 +9,24 @@
 
 
 .onAttach = function(libname, pkgname) {
-  n_omp_threads = detect_number_omp_threads()
+  n_omp_threads = getOption("rsparse_omp_threads")
+  if (is.null(n_omp_threads)) { # unlikely given .onLoad below
+    n_omp_threads = detect_number_omp_threads()
+    options("rsparse_omp_threads" = n_omp_threads)
+  }
   if (interactive()) {
-    msg = paste0("Setting OpenMP threads number to ",
+    msg = paste0("Number of OpenMP threads set to ",
                  n_omp_threads,
                  "\nCan be adjusted by setting `options(\"rsparse_omp_threads\" = N_THREADS)`")
     packageStartupMessage(msg)
   }
-
-  options("rsparse_omp_threads" = n_omp_threads)
-
 }
 
 .onLoad = function(libname, pkgname) {
   # install_name_tool_change_float()
   # library.dynam("rsparse", pkgname, libname)
-  options("rsparse_omp_threads" = detect_number_omp_threads())
+  if (is.null(getOption("rsparse_omp_threads")))
+    options("rsparse_omp_threads" = detect_number_omp_threads())
   logger = lgr::get_logger('rsparse')
   logger$set_threshold('info')
   assign('logger', logger, envir = parent.env(environment()))
@@ -37,14 +39,8 @@
 #'
 #' @export
 detect_number_omp_threads = function() {
-  n_omp_threads = as.numeric(Sys.getenv("OMP_NUM_THREADS"))
-  if (is.na(n_omp_threads) || n_omp_threads <= 0) n_omp_threads = omp_thread_count()
-  ## if OMP_THREAD_LIMIT is set, maximize on that limit.
-  omp_thread_limit = as.numeric(Sys.getenv("OMP_THREAD_LIMIT"))
-  if ( is.na(omp_thread_limit) ) omp_thread_limit = n_omp_threads
-  n_omp_threads = min(omp_thread_limit, n_omp_threads)
-
-  n_omp_threads
+  # now respects both OMP_NUM_THREADS and OMP_THREAD_LIMIT
+  omp_thread_count()
 }
 
 install_name_tool_change_float = function() {

src/utils.cpp

@@ -84,9 +84,9 @@ dMappedCSC extract_mapped_csc(Rcpp::S4 input) {
 int omp_thread_count() {
   int n = 0;
 #ifdef _OPENMP
-#pragma omp parallel reduction(+ : n)
+  int max_threads = omp_get_max_threads(), thread_limit = omp_get_thread_limit();
+  n = max_threads < thread_limit ? max_threads : thread_limit;
 #endif
-  n += 1;
   return n;
 }