default to 2 threads but give a startup message

R/onAttach.R

@@ -0,0 +1,18 @@
+
+.onAttach = function(libname, pkgname) {
+  if (!interactive()) {
+    return()
+  }
+
+  threads_option <- getOption("ranger.num.threads")
+  threads_env <- Sys.getenv("R_RANGER_NUM_THREADS")
+  if (!is.null(threads_option)) {
+    thread_string <- paste(threads_option, "threads (set by options(ranger.num.threads = N).")
+  } else if (threads_env != "") {
+    thread_string <- paste(threads_env, "threads (set by environment variable 'R_RANGER_NUM_THREADS').")
+  } else {
+    thread_string <- "2 threads (default). Change with num.threads in ranger() and predict(), options(ranger.num.threads = N) or environment variable 'R_RANGER_NUM_THREADS'."
+  }
+
+  packageStartupMessage(paste("ranger", packageVersion("ranger"), "using", thread_string))
+}

R/predict.R

@@ -193,7 +193,7 @@ predict.ranger.forest <- function(object, data, predict.all = FALSE,
   ## Num threads
   ## Default 0 -> detect from system in C++.
   if (is.null(num.threads)) {
-    num.threads = 0
+    num.threads <- as.integer(Sys.getenv("R_RANGER_NUM_THREADS", getOption("ranger.num.threads", 2L)))
   } else if (!is.numeric(num.threads) || num.threads < 0) {
     stop("Error: Invalid value for num.threads")
   }

R/ranger.R

@@ -514,7 +514,7 @@ ranger <- function(formula = NULL, data = NULL, num.trees = 500, mtry = NULL,
   ## Num threads
   ## Default 0 -> detect from system in C++.
   if (is.null(num.threads)) {
-    num.threads = 0
+    num.threads <- as.integer(Sys.getenv("R_RANGER_NUM_THREADS", getOption("ranger.num.threads", 2L)))
   } else if (!is.numeric(num.threads) || num.threads < 0) {
     stop("Error: Invalid value for num.threads")
   }